EVALUATION OF GRAFTING TECHNOLOGY  FOR 
MANAGEMENT OF BACTERIAL WILT (Ralstonia 
solanacearum) OF TOMATO (Solanum lycopersicum L) 
 
 
KANYUA S. IGNATIUS (Bsc.Agric) 
 A144/OL/22324/2011  
 
A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF 
THE REQUIREMENTS FOR THE AWARD OF THE 
DEGREE OF  MASTER OF SCIENCE (AGRONOMY) IN 
THE SCHOOL OF AGRICULTURE AND ENTERPRISE 
DEVELOPMENT OF KENYATTA UNIVERSITY 
APRIL, 2018
ii 
 
DECLARATION 
I, Kanyua S.Ignatius, declare that this thesis is my original work and has not 
been presented for the award of a degree in any other University or any other 
award.  
 
Signature: ………………………   Date:……………………….. 
Kanyua Stella Ignatius 
Department of Agricultural Science and Technology 
Kenyatta University 
 
  
SUPERVISORS 
We confirm that the work reported in this thesis was carried out by the 
candidate under our supervision as University supervisors.  
 
Signature: …………………………..  Date: …………………………… 
Dr. Maina Mwangi 
Department of Agricultural Science and Technology 
Kenyatta University  
 
Signature: ……………………………… Date: ……………………………  
Dr. Jesca Mbaka 
Department of Crop Protection  
Kenya Agricultural and Livestock Research Organization (KALRO) - Thika 
iii 
 
 
DEDICATION 
To my dear son Emmanuel Wray for his enduring love, support and 
encouragement during the period of my study. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
iv 
 
 
ACKNOWLEDGEMENT 
I feel greatly indebted to my God without whose strength and provision I 
would not have gone this far. His presence in many ways has seen me through 
this achievement. 
I would like to sincerely thank my supervisors: Dr. Maina Mwangi who 
committed himself tirelessly with patience, integrity, immense knowledge and  
supervised this work to conclusion and mentored me too. Dr. Jesca Mbaka 
your guidance and valuable criticism is highly appreciated. Njeri Njau your 
support in all ways is gratefully appreciated. 
Lots of thanks go to my parents, Ignatius Njagi and Endelina Njagi, for 
instilling in me a desire for excellence and supporting me towards this 
achievement. I am grateful to my brother Moses who despite his busy study 
schedule willingly offered his laptop for this work. I recognize Samuel for 
assisting with the technical work in the greenhouse. Appreciation goes to 
technicians in the Department of Plant and Microbial Sciences for allowing 
me to use their facilities to conduct this study. 
Finally, I thank all my friends for their prayers and support. 
 
 
v 
 
 
TABLE OF CONTENTS 
 
DECLARATION .............................................................................................. ii 
DEDICATION ................................................................................................. iii 
ACKNOWLEDGEMENT ............................................................................... iv 
TABLE OF CONTENTS ...................................................................................v 
LIST OF TABLES ........................................................................................... ix 
LIST OF FIGURES ...........................................................................................x 
LIST OF APPENDICES ................................................................................ xiii 
ACRONYMS AND ABBREVIATIONS ...................................................... xiv 
CHAPTER ONE: INTRODUCTION ............................................................1 
1.1 Tomato production in Kenya.................................................................... 1 
1.1.1 Bacterial Wilt disease ........................................................................ 2 
1.1.2 Disease management ......................................................................... 3 
1.1.3 Grafting .............................................................................................. 4 
1.2 Problem Statement ................................................................................... 5 
1.3 Justification  of the study ......................................................................... 6 
1.4 Objectives ................................................................................................. 6 
1.4.1 Overall objective................................................................................ 6 
1.4.2 Specific Objectives ............................................................................ 6 
1.5 Hypothesis ............................................................................................ 7 
1.6 Significance of the study ...................................................................... 7 
CHAPTER TWO:  LITERATURE REVIEW ..............................................9 
2.1 Background Information .......................................................................... 9 
2.1.1 Origin and botany of tomato .............................................................. 9 
2.1.2 Tomato production in Kenya ........................................................... 11 
2.2  Economic and Nutritional Importance of Tomato ................................ 13 
2.3 Constraints in tomato production ........................................................... 15 
2.4  Bacterial Wilt Disease ........................................................................... 16 
2.4.1  Ralstonia solanacearum ................................................................. 17 
vi 
 
2.4.2 Biology and Ecology of Bacterial wilt ............................................ 19 
2.4.3 Bacterial Wilt Management ............................................................. 20 
2.4.5 Biological control options ............................................................... 22 
2.4.6 Chemical control  options ................................................................ 23 
2.4.7 Host resistance control  options ....................................................... 25 
2.5 Grafting .................................................................................................. 27 
2.5.1  Grafting in bacterial wilt management ........................................... 30 
2.5.2 Compatibility of scion and rootstock in grafting ............................. 31 
2.5.3 Grafting methods ............................................................................. 33 
2.5.4 Physiological aspects of rootstock–scion interaction ...................... 34 
2.5.5 Hormonal aspects of rootstock–scion interactions .......................... 36 
2.5.6 Healing Process ............................................................................... 37 
2.6 Potential sources of rootstocks for grafting tomato ............................... 38 
2.6.1 Capsicum ......................................................................................... 38 
2.6.2 Eggplant ........................................................................................... 38 
2.6.3 Sodom Apple ................................................................................... 38 
2.6.4 Resistant tomato cultivar ................................................................. 39 
CHAPTER THREE: MATERIALS AND METHODS .............................40 
3.1 Survey..................................................................................................... 40 
3.1.1 Survey site ....................................................................................... 40 
3.1.2 Survey data collection ..................................................................... 42 
3.2 Grafting experiments .............................................................................. 43 
3.2.1 Experimental site ............................................................................. 43 
3.3  Selection of plants for use as scion and rootstocks ............................... 43 
3.4 Establishment of seedlings  for scion and rootstock in the nursery ....... 44 
3.5.1 Sample Selection ............................................................................. 44 
3.5.2 Media preparation ............................................................................ 45 
vii 
 
3.5.3 Isolation of R. solanacearum colonies ............................................ 46 
3.5.4 Inoculation of plants with R. solanacearum .................................... 46 
3.5.5 Observations and Data recording .................................................... 47 
3.6.1 Raising of seedlings ......................................................................... 48 
3.6.2 Grafting of the susceptible scions onto selected resistant rootstock 49 
3.7 Evaluating resistance of grafted seedlings to bacterial wilt ................... 49 
3.8 Evaluating the effect of plant growth stage on grafting practices .......... 50 
4.0 Experimental design and Data analysis .................................................. 50 
CHAPTER FOUR:  RESULTS ....................................................................51 
4.1 Survey Results ........................................................................................ 51 
4..1.1 Variety of tomatoes grown by farmers ............................................... 51 
4.1.2 Source of planting materials ............................................................ 53 
4.1.3 Tomato Production challenges ........................................................ 53 
4.1.4 Crop Management Strategy ............................................................. 59 
4.2 Identification of bacterial wilt resistant germplasm for use as rootstocks
 ...................................................................................................................... 61 
4.3 Compatibility of bacterial wilt resistant rootstocks to scions of preferred 
tomato cultivars ............................................................................................ 63 
4.3.1: Grafting of the susceptible scion onto resistant rootstock .............. 63 
4.3.2 Compatibility of the resistant rootstock and susceptible scions .......64 
4.3.3 Sodom apple as rootstock ................................................................ 64 
4.3.4 Mt56 as rootstock ............................................................................ 65 
4.3.5 Eggplant rootstock + Cal J scion grafts ........................................... 65 
4.3.6 Inoculation of grafted seedlings ...................................................... 66 
4.3.7 Plant performance after transplanting the uninoculated grafted plants
 .................................................................................................................. 67 
4.3.8 Plant Height ..................................................................................... 67 
4.3.9 Number of leaves ............................................................................. 68 
4.3.10 Flowering ....................................................................................... 68 
viii 
 
4.3.11 Fruit yield in grams........................................................................ 69 
4.3.12 Plant performance after inoculation with Bacterial wilt pathogen 70 
4.3.13 Number of leaves ........................................................................... 73 
4.3.14 Mean number of flowers................................................................ 75 
4.3.15 Fruit yield ...................................................................................... 77 
4.4 Effect of stage of growth on success of grafting .................................... 77 
CHAPTER FIVE:  DISCUSSION ................................................................79 
5.1 Tomato production in Mwea East .......................................................... 79 
5.2 Management of pests in tomato production ........................................... 80 
5.3 Technologies used in management of Bacterial wilt: Nursery production
 ...................................................................................................................... 82 
5.4 Cultural practices used for control of Bacterial wilt: Crop Rotation ..... 82 
5.5 Use of resistant varieties ........................................................................ 83 
5.6 Compatibility of bacterial wilt resistant rootstocks ................................ 83 
5.7 Effect of grafting practice and growth stage on success of grafting ...... 86 
CHAPTER SIX:  CONCLUSION AND RECOMMENDATIONS ..........88 
6.1 Conclusions ............................................................................................ 88 
6.2 Recommendations .................................................................................. 88 
REFERENCES ...............................................................................................90 
APPENDICES ..............................................................................................107 
Appendix 1: Questionnnare ........................................................................ 107 
Appendix 2: PHOTO card .......................................................................... 115 
Appendix 3: ANOVA Tables ..................................................................... 117 
 
 
 
 
 
 
 
 
ix 
 
LIST OF TABLES 
Table 1: Production of tomato in selected counties in Kenya .................... 12 
Table 2: Some of the common fungicides and their Active ingredients 
used in tomato production in Mwea East ................................. 57 
Table 3: Insecticides and their Active ingredients commonly used in 
tomato production ....................................................................... 59 
Table 4: Mean number of surviving plants following inoculation with R. 
solanacearum ............................................................................... 62 
 
x 
 
 
LIST OF FIGURES 
Figure 1: Conceptual Framework .................................................................. 8 
Figure 2: Kirinyaga County map showing locations of  survey 
(Murinduko, Nyangati and Tebere) in blue arrows................. 41 
Figure 3: Respondents (n=100) growing different types of tomato varieties          
in Mwea East Sub-County .......................................................... 52 
Figure 4: Area of tomato production grown by farmers in Mwea East Sub 
county ........................................................................................... 52 
Figure 5: Source of tomato planting materials used by farmers in Mwea 
East Sub - county......................................................................... 53 
Figure 6: Tomato diseases experienced by tomato farmers in Mwea East
 ....................................................................................................... 54 
Figure 7: Pests affecting tomato farmers in Mwea East sub county ......... 55 
Figure 8: Common fungicides used in tomato production in Mwea East 56 
Figure 9: Common insecticides used in tomato production in Mwea East
 ....................................................................................................... 58 
Figure 12: Proportion (%) of grafted plants fully healed /established 
fourteen days after grafting ....................................................... 63 
Figure 13: Mean height of grafted tomato seedlings after transplanting . 67 
Figure 14: Mean number of flowers of tomato seedlings after 
transplanting................................................................................ 69 
Figure 15: Mean yield of fruits produced by grafted tomato seedlings.  
Error bars 95% Confindence interval ...................................... 70 
Figure 16: Mean height of Anna F1 grafted plants inoculated (A), and 
uninoculated (B) .......................................................................... 72 
Figure 17: Mean height of Cal J grafted plants inoculated (A), and 
uninoculated (B) .......................................................................... 73 
Figure 18: Mean number of leaves on seedlings of tomato cultivar Anna 
F1 grafted on Mt56, Sodom apple and Eggplant. The number 
of leaves was recorded weekly .................................................... 74 
xi 
 
Figure 19: Mean number of leaves on seedlings of tomato cultivar Cal J 
grafted on Mt56, Sodom apple and Eggplant. The number of 
leaves was recorded weekly ........................................................ 75 
Figure 20: Mean number of flowers produced by the inoculated and  
uninoculated  grafted tomato plants with Anna F1 scions ...... 76 
Figure 21: Mean number of flowers produced by the inoculated and  
uninoculated  grafted tomato plants with Cal J scions ............ 76 
Figure 22: Yield of fruits produced by inoculated and uninoculated 
tomato plants. Error bars 95% Confidence Interval ............... 77 
Figure 23: Proportion (%) of successfully grafted plants at two growth 
stages ............................................................................................ 78 
 
 
xii 
 
 
                                         LIST OF PLATES 
Plate 1: Rootstock seedlings transplanted in polybags ............................... 44 
Plate 2: Infected tomato stem with bacteria oozing into distilled water ... 45 
Plate 3: Isolated colonies of R. solanacearum in TZC Media (a) (F – non-
virulent and G – virulent colonies) and Sub- cultured colonies 
of R. solacearum (b) ..................................................................... 46 
Plate 4: Wilted plant (a) and vascular discoloration (b) of Capsicum plant 
after inoculation with R. solanacearum ..................................... 48 
Plate 5: Infected Capsicum (a) and Cal J (b) after inoculation compared to 
uninfected Solanum incarnum (c) and Solanum melongena (d) 
four weeks after Inoculation ...................................................... 62 
Plate 6: Sodom apple + Cal J with bent roostock (extreme right) and the 
other plant with thin rootstock than the scion (left side) ......... 64 
Plate 7: Healthy grafted plants of  Mt56 + Cal J with the rootstock and 
scion having the same diameter ................................................. 65 
Plate 8: Healthy grafted plants of Eggplant + Cal J  with same diameter 
of rootstock and scion fourteen days after grafting ................. 66 
Plate 9: Healthy grafted plants of Eggplant + Cal J (A); wilted plants of 
ungrafted susceptible Cal J (B) two weeks after inoculation .. 66 
 
 
 
 
 
 
 
 
 
 
 
 
xiii 
 
LIST OF APPENDICES 
Appendix 1: Questionnaire 
Appendix 2: PHOTO card 
Appendix 3:  ANOVA Analysis Table  
xiv 
 
 
ACRONYMS AND ABBREVIATIONS 
AMF   Arbascular Mycorhizal Fungi 
ANOVA  Analysis of Variance 
AVRDC  Asian Vegetable Research and Development Center 
CABI   Centre for Agriculture and Biosciences International 
CRD   Completely Randomized Design 
GoK   Government of Kenya 
HCDA   Horticultural Crops Development Authority 
KALRO  Kenya Agricultural and Livestock Research                        
   Organization 
LSD   Least Significant Difference 
MRLS   Maximum Residue Levels 
OARDC  Ohio Agricultural Research and Development Center 
OPV   Open Pollinated Varieties 
PGPR   Plant Growth Promoting Rhizobacteria 
PCR   Polymerase Chain Reaction 
USDA   United States Department of Agriculture 
xv 
 
ABSTRACT 
Tomato (Solanum Lycopersicun L) is a very important vegetable grown 
mainly by small scale farmers in most arable areas in Kenya. Tomato 
production has declined drastically due to attack by Ralstonia solanacearum, a 
soil borne pathogen which causes bacterial wilt. Transmission of pathogen 
occurs when bacterial ooze from the plant enters the surrounding water or soil, 
contaminates farming equipment or by insect vectors. The disease has not yet 
been effectively managed. Grafting is an asexual plant propagation technique 
that involves joining the scion of desirable cultivar onto a resistant rootstock 
of another compatible species. The overall objective of the study was to 
investigate the potential use of grafting technique for the management of 
bacterial wilt in tomato. A survey was first conducted in Kirinyaga County to 
determine the important pests, pathogens, tomato varieties grown and other 
key tomato production constraints. Secondly, rootstocks comprising varieties 
from the Solanaceae family namely Solanum melongena, Capsicum annum L., 
Solanum incarnum and the bacterial wilt resistant tomato cultivar (Mt56) were 
evaluated. A tomato cultivar well adapted to greenhouse environment (Anna 
F1) and one grown under field conditions (Cal J) were used as the scion 
material. Bacterial inoculum isolation was done using CPG Medium and TZC 
was used to identify distinct colonies of R. solanacearum. Pathogen inoculum 
was introduced to the test plants and disease severity data recorded using 0 to 
5 scoring scale. Growth vigor of the inoculated and uninoculated seedlings and 
number of days to wilting were recorded. Data were subjected to ANOVA 
using Genstat version 15 and significantly different treatment means separated 
using LSD at P < 0.05. Solanum melongena, Solanum incarnum and bacterial 
wilt resistant tomato cultivar (Mt56) did not develop infection and were used 
as rootstocks for grafting to susceptible scions to check for compatibility and 
confirm effectiveness. The Capsicum annuum had a 5 scale disease severity 
and was not further studied. From the survey results, the highest proportion by 
gender engaged in tomato production is male. The greatest challenge affecting 
tomato production in Mwea East locations was bacterial wilt. Grafting was 
done when seedlings were at 2-3 leaf stage and cleft grafting method was 
used. The rootstocks and scions were compatible on Mt56 + Anna F1 (93.30% 
take), Mt56 + Cal J (76.7% take), S. melongena + Anna F1 (96.7% take), S. 
melongena + Cal J (83.3% take), S. incarnum + Anna F1 (73.3% take), and S. 
incarnum + Cal J (100% take). Grafted plants had higher survival percentage 
and reduced disease severity as compared to the ungrafted susceptible Cal J. 
From the study, it was concluded that farmers have limited information on 
bacterial wilt and use less effective management strategies. Additionally, 
resistant germplasm to bacterial wilt exists and can be successfully utilized to 
graft susceptible tomato cultivars and contribute to management of bacterial 
wilt at 2-3 leaf stage. It is recommended that, further studies on other 
solanaceous varieties with potential for use in tomato grafting should be 
conducted, need for cost benefit analysis of the tomato grafting technology 
and more research and experimental work to test resistant varieties which do 
not require grafting to be conducted. 
1 
 
 
CHAPTER ONE: INTRODUCTION 
1.1 Tomato production in Kenya 
Tomato is amongst the important vegetables worldwide and Kenya, with a 
total of 611.4 tones traded in 2011 worth 39.46 billion Kenya shillings 
(Muchangi, 2012). Tomatoes are grown mainly by small scale farmers in 
Central Kenya’s main production areas of Kirinyaga, Kiambu, Nyeri and 
Maragwa (Waiganjo et al., 2006). Tomato is also grown in almost all counties 
between 1150 and 1800 m above sea level. It has gained importance as an 
income generating crop in peri-urban and high potential areas in the past 
decade and was ranked first in a prioritization of vegetable crops value chains 
in Kenya (Mbaka et al., 2013). 
The area under production in 2015 was 19,021 ha producing 402,513 tones 
while in 2016, the area under production was 21,921 ha with 410,033 tones 
estimated production (Factfish website, 2016). In 2014, the total national 
production was 400,204 tones valued at 11.8 billion Kenya shillings. The area 
under production in the same year increased from 20,985 ha to 24,074 ha 
representing a 15% increase. The quantity and value increased from 383,868 
tones to 400,204 tones and value from 11.6 to 11.8 billion Kenya shillings 
representing 4.0% of quantity produced and 1.3 % of value respectively 
(HCDA, 2014). For premium quality and high yield, tomatoes require a 
relatively cool and dry climate. However, it is adapted to wide climatic 
conditions ranging from temperate to hot and humid tropics. Tomatoes react to 
variation of temperature during the growth cycle, particularly during seed 
2 
 
 
germination, seedling growth, flowering, fruit set and fruit quality (Naika et 
al., 2005). 
1.1.1 Bacterial Wilt disease 
Bacterial wilt, caused by Ralstonia solanacearum is a soil borne disease of 
tomato (Sikoru et al., 2004). Ralstonia solanacearum is a serious obstacle to 
the cultivation of several solanaceous plants in both temperate and tropical 
regions. The greatest economic damage has been reported on tomatoes, 
tobacco and potatoes and sometimes can cause up to 90% crop loss 
(Mallikarjun et al., 2008). The disease  has been ranked as the most severe 
constraint to production of tomatoes (CABI, 2005a). Severity of the disease 
mostly increases if root nematodes occurs in association with R. solanacearum 
(Deberdt et al., 1999).   
Nematode infestation in tobacco changes the plants physiology, increasing 
susceptibility to bacterial wilt (Chen, 1984). In India, experiments showed that 
the combined pathogenic effects of root-knot nematodes (Meloidogyne 
javanica) and R. solanacearum were greater than the independent effects of 
either (CABI, 2005b).  
Bacterial wilt appears as flaccidity first in one or more of the youngest leaves. 
When environmental conditions are favorable, rapid and complete wilt soon 
follows 2-3 days after the appearance of initial symptoms, advanced stages of 
the disease may occur. Formation of adventitious roots is promoted by low 
temperatures and low host strain virulence. These are most pronounced when 
the disease develops slowly under conditions that are less than optimum for 
3 
 
 
disease development. Leaf epinasty may also occur when the disease develops 
slowly. In the early stages of the disease, the vascular system in the stem of a 
plant appears yellow or light brown in longitudinal or transverse section and as 
the disease progresses the system becomes darker brown. When the plant wilts 
completely, the cortex and the pith also become brown and as the disease 
progresses, the plant becomes permanently wilted with the entire root system 
showing brown rot (Jones et al., 1992). 
1.1.2 Disease management 
The disease is difficult to manage because the pathogen can survive in soil for 
long periods in association with a wide range of crops such as pepper, potato, 
capsicum, eggplants and weeds such as Jimson weed (Datura spp) and 
nightshade (Solanum nigrum). Cultural control practices such as maintaining 
good drainage and sanitation, ensuring that infected plants are not thrown into 
irrigation ditches and canals, removing plants and crop debris from the field 
after harvest and burning or deep- plow (20-30cm) should be adopted. Crop 
rotation can be effective especially when attempting to control pathogenic 
races that exhibit narrow host range with 3 – year rotations with beans, maize, 
garlic, soya bean and wheat (Allen et al., 2005). Other management practices 
such as soil solarization combined with fumigation, weed destruction, 
alternative hosts, sawdust, peat moss, nitrite fertilizers and increasing calcium 
concentration in the soil are also used to manage the disease (Mallikarjun et 
al., 2008). 
4 
 
 
1.1.3 Grafting  
Grafting is an asexual plant propagation technique that joins parts from two 
different plants so that they will grow as one, therefore, a grafted plant is a 
composite of parts derived from two or more plants (Bareja, 2011). Grafting is 
an asexual plant propagation technique that involves joining together the upper 
part of a plant (scion) of desirable cultivar onto a resistant rootstock of another 
compatible species (McAvoy, 2005). In horticulture, grafting is widely used 
for various reasons. With vegetables grown in the field, grafting is used to 
increase resistance to soil-borne diseases. Grafting technology in Kenya has 
been introduced to overcome bacterial wilt disease of tomato in high tunnels 
as well as open fields (Erbaugh et al., 2011). The success of the union is 
possibly higher among plants within the same species. However, intergeneric 
grafting is now practiced widely in propagation of plants to take advantage of 
disease resistance and more adapted rootstocks, e.g. Solanum melongena 
(eggplant) as rootstocks with tomato, both belonging to the family Solanaceae 
(Bareja, 2011). In Kenya, on-farm trials on grafting were done with Kangai 
Tisa Farmers group in Kirinyaga County using the wilt resistant rootstock of 
tomato Mt56 (Waiganjo et al., 2011). Trial results indicated that grafting 
susceptible variety to bacterial wilt such as Onyx on resistant Mt56 resulted in 
significantly less disease incidence in open field (25%) and high tunnel (15%) 
(Waiganjo et al., 2011). Despite past efforts, the bacterial wilt disease has not 
been effectively managed and thus there is need for more research. 
5 
 
 
1.2 Problem Statement 
Bacterial wilt of tomato is the most serious challenge in tomato production 
both in the conventional and in green house production systems where soil is 
used as the growth medium. The problem is compounded by the presence of 
R. solanacearum inoculum that survives for long in the soil and introduction 
of disease to new areas through tomato seedlings from uncertified nurseries. 
Moreover some farmers opt to re-cycle seeds to reduce tomato production 
cost, which could enhance disease spread. Soil sterilization by fumigation, 
solarization or heating, though effective in reducing the pathogen population, 
is not feasible due to re-introduction of the pathogen by farm workers or 
irrigation water, among other pathways. Bacterial wilt causes serious crop 
losses of up to 90% with major economic loss of investment for growers. Due 
to inability to meet market demand with fresh tomato, bacterial wilt disease 
has also resulted in loss of markets to competing processed tomato products  
e.g. ketchup, which leads to loss of employment opportunities and income 
(Mallikarjun et al., 2008). Lack of effective management options for bacterial 
wilt has led to the destruction of ecosystems as farmers shift cultivation to new 
lands that are presumed to be free of bacteria. Efforts to introduce grafting 
technology to the package of available disease management measures have 
been hindered by inadequate information on suitable rootstocks and their 
compatibility to the preferred tomato varieties. To further enhance the chances 
of successful adoption of grafting technology it is also necessary to determine 
and provide information on the appropriate stages of grafting, which is 
currently not available.  
6 
 
 
1.3 Justification  of the study 
Previous efforts to identify effective control measures for bacterial wilt have 
not yielded considerable success. Therefore, more research is needed to boost 
the ongoing efforts to identify and develop effective management strategies 
for the disease. Grafting susceptible tomato scions of preferred varieties onto 
rootstock with proven resistance to bacterial wilt is a promising strategy. 
However, this strategy has not been well researched on using varieties with 
high market demand in Kenya. This study therefore aimed at generating 
results that will inform the process of selecting resistant rootstock and the 
appropriate grafting stages and methods to increase success and adoption of 
the technology. 
1.4 Objectives 
1.4.1 Overall objective 
The overall objective of the study was to investigate the effectiveness of 
grafting technique for the management of bacterial wilt of tomato. 
1.4.2 Specific Objectives 
The specific objectives of the study were:  
1. To determine the important pests, pathogens, tomato varieties grown 
and key tomato production constraints in Kirinyaga County. 
2. Identify bacterial wilt resistant germplasm that can be used as 
rootstocks in tomato grafting.  
3. Determine compatibility of bacterial wilt resistant rootstocks to 
preferred tomato varieties. 
7 
 
 
4. Determine and recommend the appropriate grafting practices and stage 
of growth of both rootstock and scions to ensure high success rates. 
1.5 Hypothesis 
1. Bacterial disease is the major constraint in tomato production in 
Kirinyaga County. 
2. Bacterial wilt resistant germplasm do not vary in resistant for different 
rootstocks in tomato grafting. 
3. Bacterial wilt resistant plant species do not vary in compatibility with 
tomato varieties.  
4. Grafting significantly affect success of bacterial wilt management. 
1.6 Significance of the study 
Bacterial wilt (Ralstonia solanacearum) disease of tomato is the major 
challenge in tomato production and causes about 90% loss leading to low 
tomato production. The disease has been difficult to control due its large 
inoculum and long period of the pathogen survival in the soil. Management 
strategies applied to control the disease have not been successful. 
Recommendations have been made to improve on the control methods of the 
disease to ensure high tomato production. 
Recommendations from the study shall provide growers with a viable and eco-
friendly practice for bacterial wilt management that will contribute to 
sustainable tomato production in Kenya and other countries of similar 
socioeconomic status. 
 
8 
 
 
 
   
 
 
 
 
 
 
 
 
 
 
 
 
 
 
     
 
 
 
 
 
 
 
 
  
Figure 1: Conceptual Framework 
Resistant Germplasm 
(Rootstocks) 
 Eggplant 
 Sodom apple 
 Tomato Mt56 
 Capsicum 
 
 
Grafting Methods 
 Tube Grafting 
 Cleft Grafting 
 
Compatibility 
Incompatibility 
 
 
 
Tomato Germplasm 
(Scions) 
 Anna F1 
 Cal J 
 Grafting Stage 
 2 -3 leaf  
 4-5 leaf 
 
 Disease 
development 
 Severity 
 Incidence 
Plant performance 
 Plant height 
 Number of 
leaves 
 Number of 
flowers 
 Yield 
9 
 
 
CHAPTER TWO:  LITERATURE REVIEW 
2.1 Background Information 
2.1.1 Origin and botany of tomato 
Tomato belongs to the family Solanaceae which includes other well-known 
species, such as eggplant (aubergine), peppers, tobacco and potato and has 
South American Andes as its origin. The Spanish conquerors took the 
cultivated tomato to Europe in the 16th Century and from Europe, it was later 
introduced to the Middle East, Africa, Southern and Eastern Asia (Naika et al., 
2005).  
Tomato plant has rigorous tap root and radial protostele, comprising vascular 
tissue which is a solid column with the phloem located peripheral to the xylem 
(Coaker et al., 2002). The tomato plant is dicotyledous and grows as a series 
of branching stems and at the tip there is a terminal bud that does the actual 
growth. The lateral buds take over and grow into other fully functional vines 
when the tip eventually stops growing whether because of flowering or 
pruning (Rick, 1995). The vines of the tomato plant are typically pubescent, 
meaning they are covered with fine short hairs which facilitate the vining 
process, turning into roots wherever the plant is in contact with moisture and 
ground (Rick, 1995).  
The growth habit of stem ranges between prostrate and erect and grows to a 
height of 2 – 4 m; the stem is coarse, hairy, glandular and solid. The tomato 
plant has compound leaves made up of leaflets distributed along the leaf 
rachis. The leaves are 10 – 25cm long, odd pinnate with 5 - 9 leaflets each 
upto 8cm long on petioles with a serrated margin, both the leaves and stem 
10 
 
 
have dense grandular hairs (Acquaah, 2002). The leaf also contains many 
vascular bundles distributed throughout and the main vein of the leaf runs 
through the midrib (Rost, 1996). The flowers are bisexual and along the edges. 
The anthers are fused forming a column surrounding the pistil’s style, regular, 
grow between or opposite the leaves and 1.5 – 2 cm in diameter. The flowers 
are yellow in color with fine pointed labels on the two corolla. They are borne 
in a cyme of 3 - 12 together (Acquaah, 2002). Calyx tube is hairy and short, 
usually 6 petals are up to1cm in length and sepals are persistent, yellow and 
retrieved when mature, six stamens, anthers are blightly yellow in color 
surrounding the style with an elongated sterile tip. Ovary is superficial with 2 - 
9 compartments.  
The tomato fruits are diverse in shape and size ranging from round and small 
to large and variably shaped (Brewer et al., 2006). The seeds are numerous 
and pear shaped or kidney, light brown, hairy, 2 - 4 mm wide and 3 - 5 mm 
long, and in the endosperm, the embryo is coiled up (Naika et al., 2005).  
Tomatoes are subdivided into four main varieties depending on cultivation 
method, shape, weight, size and color. The most widely used are the round 
(spherical) tomatoes. Generally, red tomatoes intended for fresh consumption 
are smooth and round; beef tomatoes often also called ribbed tomatoes 
because of their shape are larger than round tomatoes. They are sometimes 
eaten fresh and are mostly used in the processing industry. Cherry tomatoes 
have a similarity in size and shape to cherries while plum tomato is a fresh, 
thick variety, low in seeds and used both for processing and fresh consumption 
(Kirimi Sindi, 2011). In Kenya, the round (spherical) tomatoes are more 
11 
 
 
preferred in market because they take less days to mature (75 days), produce 
higher yield and have better shelf life (Wambua, 2012). 
2.1.2 Tomato production in Kenya 
Tomatoes (Solanum lycopersicon L) are among the vegetable crops grown all 
year round for both domestic markets and home use. In horticultural expansion 
and development in Kenya, tomato is also amongst the promising 
commodities and accounts for 6.72% of total production and 14% of the total 
vegetable produce (GoK, 2012). It is an important cash crop for small scale 
growers with a potential for increasing incomes (Ssejjemba, 2008). In Kenya, 
tomato is also one of the most important local market vegetables with 611.4 
tones traded in 2011 worth of 39.46 billion Kenya shillings (Muchangi, 2012). 
Tomato is either grown under greenhouse technology or in open field. 
Greenhouse technology accounts for 5% while open field accounts for 95% 
(Seminis-Kenya, 2007). Greenhouse technology has attracted more educated 
youths to horticulture since it is perceived as modern, cutting edge technology 
and smart (Mbaka et al., 2013). Tomato seeds availability has been achieved 
by support from seed companies through supply of a range of varieties to meet 
farmers demand. 
In Africa, Kenya is among the leading tomato producers and is ranked 6th with 
397,007 tones of total production (FAO, 2012). In Kenya, tomato plays a vital 
role in meeting nutritional requirements, earnings and creation of employment 
(Sigei et al., 2014). The major tomato producing counties in Kenya are 
Kirinyaga (14%), Kajiado (9%) and Taita Taveta (7%) (Table 1). 
12 
 
 
Table 1: Production of tomato in selected counties in Kenya  
Counties Areas (Ha) Quantity 
(Tonnes) 
Value (Kshs) 
Millions 
Share by 
quantity (%) 
Kirinyaga 1,978 54,524 1,070 13.9 
Kajiado 1,551 36,460 990 9.1 
Taita Taveta 548 27,400 959 6.9 
Meru 420 22,214 468 5.6 
Bungoma 1,022 21,720 887 5.5 
Kiambu 930 20,972 884 5.2 
Migori 1,068 18,429 910 4.6 
Makueni 403 17,552 682 4.4 
Homabay 803 13,120 638 3.3 
Nakuru 580 10,990 257 2.7 
Machakos 314 10,240 357 2.6 
Total 18,613 397,007 12,840 100 
Source HCDA 2013 
The main tomato varieties grown in Kenya can be categorized into those 
grown in greenhouse and those grown in the open field. Varieties grown in the 
green house include Anna F1, Nemoneta F1, Corazon F1, Tylka F1, Claudia 
F1, Chonto F1 and Prostar F1 (Monsanto, 2013).  
In the field production system the open pollinated varieties (OPV) commonly 
grown include Riogrande and Cal J (Monsanto, 2013). The main marketing 
channels for tomatoes include open air market through middle men, 
supermarkets and grocery chains as well as local hotels (Wiersinga et al., 
13 
 
 
2008). In the recent past, well established market linkages have emerged 
between farmers and the market in sub-contract supply arrangements with 
leading grocery chains such as fruit and juice, Zucchini and specialized 
vegetable markets in Westlands and Parklands in Nairobi, Kenya (Monsanto, 
2013). The produce marketed in the bigger cities that is Nairobi, Mombasa, 
Nakuru, Kisumu, Eldoret and other major towns are sourced from Kirinyaga 
(Mwea area), Meru, Kajiado, Kiambu, Bungoma, Migori, Makueni and 
Homabay Counties (HCDA, 2011). In Kirinyaga County and Loitoktok 
(Kajiado County), tomato is being produced in Mwea and Namelock irrigation 
schemes (HCDA, 2014).  
Hybrid varieties such as Eden F1, Assila F1, Kilele F1, Valoria F1, Shanty F1, 
Nuru F1 and Tropicana F1 have been introduced that produce increased yield 
and are disease tolerant (Monsanto, 2013). These varieties have replaced 
earlier ones such as Kentom, Caltana, Manset, Fortune, Money maker, Rotade, 
Neema 1400 and Neema 1200 (Wiersing et al., 2008) which are no longer 
popular with farmers.  
2.2  Economic and Nutritional Importance of Tomato 
Tomato fruit can be eaten fresh or in processed forms. The three majors 
processed products are tomato preserves (whole pealed, juice, pulp, puree, 
paste, prickled tomatoes); dried tomatoes (powder, flakers, dried tomato fruits) 
(CABI, 2005) and tomato - based foods (tomato soup, ketchup, chilli sauce, 
juice) and can also be dried (HCDA, 2010). Although botanically a fruit, 
tomatoes are served as vegetables because they are nutritious and  provide 
good quantities of vitamins A and C (Ssejjemba, 2008), they contain water 
14 
 
 
(more than 90%), and therefore are used as diuretics and help in elimination of 
toxins (USDA, 1999). Vitamin A is important for cell division, bone growth 
and maintaining the surface lining of eyes and differentiation for immune 
system regulation, intestinal tracts, urinary and respiratory systems. Vitamin C 
is essential in collagen formation, a protein that gives structure to muscles, 
cartilage, bones, blood vessels and also aids in the absorption of iron, an 
important mineral in red blood cell formation (Purseglove, 1979).  
Tomatoes have alkaline power to neutralize excess acids in the body (USDA, 
1999). They are also rich in minerals such as iron, potassium, phosphorus, 
magnesium and calcium which are important to well - balanced human diet 
(Srinivasan, 2010). Tomato juice is known to be effective for liver and 
intestinal disorders (Wamache, 2005).  
Potassium helps in prevention of high blood pressure and reduces chances of 
heart diseases. Potassium also aids in muscle contractions and may reduce the 
risks of kidney stones and bone loss. Tomatoes reduce blood clots and 
inflammation and also contain fibres that aid digestion, thereby preventing 
constipation (Purseglove, 1979). 
Dried and canned tomatoes are processed products of economic importance.  
Tomato fruit also contains high levels of lycopene, one of the most powerful 
natural antioxidant compounds responsible for the red color of tomatoes. It is a 
phytochemical which has been found to have powerful anti – cancer properties 
against prostrate cancer, especially in cooked tomatoes (USDA, 1999). 
Lycopene has also been shown to improve the ability of the skin to protect 
against harmfurl UV rays. Consumption of tomato has been associated with 
15 
 
 
decreased head, neck, colon, lung, pancreas and breast cancers (Evanelia et 
al., 2005) and might be strongly protective against neuro - degenerative 
diseases (Fall et al., 1999; Rao and Balachandran, 2002; Suganuma et al., 
2002 and Srinivasan, 2010). They have also been found to prevent heart and 
age related diseases (AVRDC, 2003). 
2.3 Constraints in tomato production 
Despite its contribution to alleviation of poverty, the tomato industry is faced 
with a myriad of constraints. These include drought, agronomic constraints 
like physiological disorders (cracking, sunburn or scald), pests and diseases, 
high perishability, poor post-harvest technologies, poorly organized rural and 
urban market infrastructures and unpredictable prices (Geoffrey et al., 2014). 
These constraints adversely affect the production and marketing of tomato and 
should be managed prudently through improvement of production techniques 
and periodic monitoring in order to develop a robust, productive and 
sustainable tomato value chain. According to Kelly and Byerlee (2004), of an 
estimated 60% of Africa’s rural population lives in good agricultural potential 
areas, but face poor market access for their produce. Therefore, improvement 
of access to market by provision of affordable and better transportation is 
deemed necessary for enhancing commercialization in developing countries 
like Kenya (Shilpi and Umali- Deininger, 2008).  
In Kenya, the whole portion of produced tomatoes is marketed locally and 
around East African countries leaving nothing for the international market. 
The key constraints that causes no export market for Kenyan tomatoes include 
16 
 
 
poor health standards for tomatoes, poor quality and unpredictable supply of 
substantial quantities of the commodity in the market (Humphrey, 2009). 
Tomato production constraints reported in Kenya include use of substandard 
varieties (HCDA, 2010), pests and diseases and high costs of management and 
limited funds to improve productivity. Tomatoes are highly perishable and 
most farmers have no access to effective transport to distant markets at the 
required time (Ssejjemba, 2008). The major tomato pests are African 
bollworm, thrips, spider mites, nematodes and white flies. The main diseases 
on tomatoes are blossom end – rot, powderly mildew, bacterial wilt, late 
blight, leaf spot, early blight, leaf curl and tomato spotted wilt virus (Waiganjo 
et al., 2006). One of the most challenging diseases is bacterial wilt. Measures 
to control some of the diseases are already available. For example, early blight 
has been effectively controlled using fungicides, e.g. Mancozeb 80WP and 
powdery mildew is controlled using Sulfur 90WP while cultural measures 
have been effective in control of  leaf spot disease.  
2.4  Bacterial Wilt Disease 
Ralstonia solanacearum (Bacterial wilt causal agent ) is mostly caused by race 
1 strain. Race 1 strain has a wide host range and can survive in the soil for a 
long period of time.  
 
Race 1 strains are highly variable in their genotype and aggressiveness on 
tomato. Some highly aggressive strains can cause severe symptoms, even on 
“resistant” varieties (Jaw and Chih, 2005). In the United States, race 1 is 
17 
 
 
endemic and can cause bacterial wilt on several major crops such as tobacco, 
potato, pepper and eggplant (Allen, 2009). It is a soil-borne and vascular wilt 
disease widely distributed in tropical and humid subtropical countries 
(Deberdt et al., 1999). The pathogen can persist for extended period (up to 40 
years) in soil, in infected debris of host plant or by colonizing volunteer 
tomato plants, alternative hosts or even non- host plants. In the absence of the 
host, the pathogen can survive between 1–3 years once it establishes itself 
(Messiha, 2006). Symptom expression is favored by high temperatures 
ranging between 29-35°C and after infection the symptoms may progress 
rapidly. However, symptomless plants may remain latently infected for 
extended periods of time under favorable conditions. Wilting is caused by 
bacteria invading and gradually blocking the vascular tissue (Sikora, 2004). 
Once established in a field, spread may occur from plant-to-plant when 
bacteria move from roots of infected plants to roots of healthy plants (Olson, 
2005). 
2.4.1  Ralstonia solanacearum 
This is a Gram – negative aerobic plant pathogenic bacterium. Ralstonia 
solanacearum is motile and soil-borne with a polar tuft flagella and colonizes 
the xylem, causing bacterial wilt in potential host plants of a very wide range. 
Ralstonia solanacearum is a destructive pathogen in many economically 
important crops like tomato, eggplant, groundnut, pepper and potato 
(AVRDC, 2008). The pathogen species is subdivided into races based on host 
range and the primary means of identifying the pathogen into races 1, 2 and 3 
18 
 
 
is the polymerase chain reaction (PCR). The species is also subdivided into 
biovars based on the utilization of the disaccharides lactose, cellobiose, 
maltose, dulcitol, mannitol and oxidation of the hexose,  alcohols, and sorbitol 
(Olson, 2005). Ralstonia solanacearum is currently the most intensively 
studied phytopathogenic bacterium due to its devastating lethality and in 
tomato, bacterial wilt is a model system for investigating mechanisms of 
pathogenesis. 
In agricultural fields, inoculum sources and dissemination methods include 
infested soil and weeds, surface and irrigation water, contaminated farm 
equipments, aquatic weeds and latently infected vegetative propagative 
material. Ralstonia solanacearum infects via the roots, moves systematically 
through the xylem and causes the wilting symptoms that are lethal (Schaad et 
al., 2001). The bacteria are spread into the plant where they multiply after 
reaching the large xylem elements. Once the bacteria is established in the 
xylem vessels, they are able to enter the parenchyma cells’ intercellular spaces 
in the cortex and pith in the plant’s various tissues. Once inside the host, the 
bacterium has affinity for the vascular system where it multplies filling the 
xylem elements rapidly with bacterial cells and slime (Gupta and Thind, 
2006). It is able to dissolve the cell walls creating slimy pockets of cell debris 
and bacteria rapidly. 
The first parts of the tomato plant to be affected are the youngest leaves and 
usually at the warmest time of day, they have a flaccid appearance. The 
symptoms of the disease appear as yellowing of the oldest leaves during 
19 
 
 
fruiting and progress to younger leaves gradually. Other plants wilt mainly 
during the heat of the day and may remain alive. The vascular tissue becomes 
brown in the roots and main stem, extending upto 10 inches above the ground 
(Stere, 2011). No leaf spots are evident and eventually the entire plant 
collapses and white runny bacterial ooze is observed from cut stems. In later 
stages of the disease, decay of the pith may cause extensive stem hollowing.  
Affected roots decay, becoming dark brown in color and if the soil is moist, 
diseased roots become soft and slimy. To distinguish bacterial wilt from 
vascular wilts caused by fungal pathogens, bacterial streaming from infected 
plant material can be observed. For quick field diagnosis, a diseased stem 
section is cut two to three centimeters (2 - 3 cm) from the base (CABI, 2005) 
and  placed against the inside wall of a water-filled clear beaker or test tube so 
that the end of the section touches the water surface. Milky white strands 
containing bacteria and extracellular polysaccharide will stream from the cut 
ends of the xylem elements (Olson, 2005) in 3- 5 minutes and if the stem is 
severely infected, the water becomes completely milky in 10 – 15 minutes. A 
common pathogen sign that is observed at the surface of freshly-cut sections 
of severely infected stems is a sticky, milk white exudate, indicating the 
presence of dense masses of bacterial cells in infected vascular bundles, and 
particularly in the xylem (Allen, 2009).  
2.4.2 Biology and Ecology of Bacterial wilt 
Ralstonia solanacearum can survive in diseased plants or plant debris, wild 
hosts, vegetative propagative organs like tubers or seeds. The pathogen can 
20 
 
 
also thrive for a long time (up to 40 years) in pure water and the bacterial 
population is reduced in extreme conditions such as high temperatures, salts 
and pH (Fajinmi et al., 2010). Ralstonia solanacearum can also survive in the 
soil for extended period in the absence of host plants and the survival period 
varies considerably depending on host race of the pathogen and on the 
chemical, physical and biological factors of the soil (Jones et al., 1992). 
Ralstonia solanacearum infects host plants primarily through wounds formed 
by lateral roots emergence or by damage caused by soil borne pathogens such 
as nematodes. The pathogen can also enter plants by way of stem injuries 
caused by insects or from mechanical damage (Agrios, 1988). Once inside 
stems or roots, the bacterium colonizes the plant through the xylem in the 
vascular bundles establishing a systemic infection that results in bacterial wilt 
(Momol et al., 2005). Wilting occurs 2 – 5 days after infection depending on 
host susceptibility, temperature and virulence of the pathogen. Infection and 
disease development are favored by high temperatures (optimum 30 –  35 
oC.),  
high moisture  (Coyne et al., 2007) or any other physical means (Stere, 2011). 
The disease development is also favored by slightly acidic soil (pH<7.0) and 
can occur on all types of soil including clay and sandy types (Fajinmi et al., 
2010).  
2.4.3 Bacterial Wilt Management  
Cultural and Phytosanitary control options 
The control of R. solanacearum is challenging once the pathogen has infested 
the soil (Jones, 2008). Even with the effort of farmers to adopt integrated 
21 
 
 
disease management strategies such as crop rotation, cultural practices and use 
of resistant cultivars, limited success has been recorded (Mbaka et al., 2013). 
Among the cultural practices, crop rotation, intercropping or incorporation of 
green manure crops such as hemp (Crotovorajuncea L.) and mung bean 
(Vignaradiata L.) have been reported to be effective for the control of 
bacterial wilt (Abedayo et al., 2009). The infection by this disease can be 
significantly reduced by using non – susceptible crops and crop rotation for 5 - 
7years (Smith et al., 1995). 
 Use of crop rotation has been shown to reduce disease incidence but the 
management is limited because the pathogen is able to survive in the soil over 
extended period of time. The pathogen is also complicated by the existence of 
alternate hosts such as Jimson weed (Datura spp), nightshade (Solanum 
nigrum) and other volunteer crops of solanaceae family (Fajinmi et al., 2010). 
In conjuction with crop rotation, weed control can be effective in reducing 
disease incidence (Allen et al., 2005). Control of weeds in the field is 
necessary because weeds serve as hosts for bacteria. Root-knot nematodes 
provide wounds that favor infection (Gupta and Thind, 2006). Rotation of 
crops with a non-suceptible crop provides some control, but this can be limited 
as the disease has a very wide host range (Saddler, 2005). There is some 
significant reduction of the disease when organic manure is used as 
demonstrated by Islam and Toyota (2004) where disease was suppressed when 
poultry and farmyard manure was added to the soil. The effect is due to 
increased microbial activity. The application of the organic amendments and 
22 
 
 
compost releases biologically active substances from crop residues and soil 
micro – organisms such as allelo chemicals, which have been reported to 
reduce the disease (Chellemi et al.,1997). In locations where the pathogen is 
not present, it is critical to prevent introduction and if inadvertently 
introduced, subsequent movement of the pathogen should be prevented.  
Planting certified disease free seedlings from registered propagators, 
disinfecting equipments after working in a field, controlled use of flood 
irrigation and avoiding overhead irrigation can reduce spread of the disease 
(McCarter, 1991). Potentially infected sites should be monitored by growers 
for early detection and subsequent eradication of pathogen (Fajinmi et al., 
2010). Weeds can also host the pathogen and their control will contribute to 
disease management especially those around the tomato field and irrigation 
reservoirs (Momol, 2005; Champoiseau and Momol, 2009). 
2.4.5 Biological control options 
Use of biological control products for soil borne pathogens has gained 
popularity in recent years due to environmental concerns raised on the use of 
chemical products (Haas and De Fago, 2005). Biological control methods have 
been widely accepted and advocated as best practice in sustainable agriculture. 
The biggest potential of biological control being micro-organisms, arbuscular 
mycorrhizal fungi (AMF) (Sharma and John,  2002; Tahat et al., 2010) and 
naturally occurring antagonistic rhizobacteria such as Pseudomonas spp and 
Bacillus spp. (Guo et al., 2004). Use of AMF in agricultural crops can provide 
protection against soil-borne pathogens by reducing the root diseases caused 
23 
 
 
by a number of soil pathogens (Sharma et al., 2004). A number of mechanisms 
are involved in the control and suppression of the pathogen by mycorrhizal 
fungi among them lignification of cell wall, changed nutrition and exudation 
of low molecular weight compounds (Chellemi et al., 1997; Tahat et al., 
2011). 
Other biological agents that have been used in disease management include 
flourescent pseudomonas such as Pseudomonas flourescens through 
production of antimicrobial substances, competition for space, nutrients and 
indirectly through induction of systemic resistance (Kavitha and Umesha, 
2007). Bacteriophages which are capable of attacking R. solanacearum have 
also been used in biocontrol. Strains that produce plant growth promoting 
rhizobacteria (PGPR) are reported to be a promising biocontrol agent for the 
pathogen. A fungus, Phythium oligandrum has been reported by Akira et al. 
(2009) to surpress bacterial wilt caused by R. solanacearum but is yet to be 
produced and formulated for use on a commercial scale. 
2.4.6 Chemical control  options 
Bacterial control using chemicals is a challenge because of the pathogen 
ability to survive in the soil and its location inside the xylem. There are no 
known chemical control of the bacterial wilt disease (Hartman et al., 1994), 
while others reported that it is difficult to control bacteria with chemicals 
(Grimault et al., 1994). Earlier use of banned soil fumigants such as Methyl 
bromide in control of bacterial wilt disease was effective but did not succeed 
(Chellemi et al., 1997). Ji et al. (2005) reported the control of bacterial wilt by 
24 
 
 
use of phosphoric acid. Soil treatments, including soil pH modification, 
solarization and application of stable bleaching powder reduced bacterial 
population and disease severity on a small scale (Saddler, 2005). There is a 
report of significant control of R. solanacearum with application of urea 
fertilizer as well as Nitrite form of fertilizers such as Potassium Nitrate. The 
fertilizers are capable of reducing the bacterial population if applied. 
Increasing calcium concentration in the soil have better control of wilt disease 
but their use on commercial scale has not yet been tested (Mallikarjun et al., 
2008). Applications of sawdust and peat moss are also efficient in reducing 
bacterial wilt incidence. 
Use of chemical products also contributes to environment degradation apart 
from being labor intensive and expensive (Fajinmi et al., 2010). In Taiwan, 
bacteriocide Terlai, has been tested under both field conditions and 
greenhouse (Hartman et al., 1994). It was foud that chemical control through 
soil fumigation and antibiotics (Tetracycline, Ampicillin, Streptomycin and 
Penicillin) shown little suppression of the pathogen. Application of a 
resistance inducer such as acibenzolar - S – Methyl (Actigard- Syngenta) or in 
combination with moderately resistant varieties can give increased control 
against the disease. Similarly, application of another product Thymol, a plant – 
derived volatile chemical has also shown positive results (Champoiseau and 
Momol, 2009). 
25 
 
 
2.4.7 Host resistance control  options 
Use of host plant resistance to control bacterial wilt in the field has been 
difficult due to lack of resistance in tomato and the nature of the pathogen. In 
tobacco, the presence of a major resistance gene has led to the development of 
genotypes that are capable of hypersensitive response, characteristic of a gene-
for - gene interaction (Robertson et al., 2004). However, to date, a similar 
major resistance gene has not been found in tomato, and plant breeders 
continue to be eluded by the complexity of this pathosystem. Development of 
horticulturally acceptable tomato varieties with resistance to bacterial wilt in 
the field has been a significant challenge.  
Being controlled quantitatively and strongly influenced by environmental 
conditions such as moisture, soil temperature and pH, resistance is complex 
(Scott et al., 2005). The complex diversity of pathogenic Ralstonia strains has 
led to the development of resistant lines which are effective in some growing 
regions and not effective in others (Scott, 1996). Historically, the pathogen 
(Ralstonia solanacearum) of tomato have been in the race 1 group, and could 
be derived from biovar 1, 3, or 4. Tomato genotypes with bacterial wilt 
resistance originated from wild tomato, particularly L. esculentum var. 
cerasiforme and L. pimpinellifolium. However, the exact nature of bacterial 
wilt resistance inheritance is a topic of debate among plant breeders because 
genetic evidence supports the presence of single gene resistance and 
oligogenic resistance (Scott et al., 2005). 
26 
 
 
Early investigations of physiological mechanisms involved with bacterial wilt 
resistance in tomato suggested that host resistant genotypes physically limit 
bacteria movement from the soil environment into the collar and mid-stem 
portions of the plant (Grimault et al., 1994). Host resistance is the most 
economical control option, though it is difficult to obtain cultivars with 
suitable resistance across locations (Abedayo et al., 2009). Resistance of the 
crop is overcome often by the genetic diversity of the pathogen as well as 
genotype – by - environment interactions (Nguyen and Ranamukhaarachchi, 
2010). 
Host resistance is an efficient and effective component in integrated 
management of bacterial wilt disease and some tomato cultivars provide 
moderate resistance against bacterial disease (Peregrine, 1982). This has been 
made possible by genetic improvement on varieties to increase tolerance 
against Ralstonia solanacearum (Liao et al., 1998). The use of resistant 
varieties has been reported to be the most effective and practical method to 
control bacterial wilt (Black et al., 2003; Grimault et al., 1994). Ralstonia 
solanacearum is a complex heterogeneous species group with a wide host 
range (Kelman et al., 1961). High variability in its biochemical properties 
(Cuppels, 1978; Hayward, 1964), serological reactions (Schaad et al., 1978), 
membrane proteins (Dristig and Dianese, 1990) and phase susceptibility 
(Okabe and Goto, 1963) confirm the existence of distinct strains posing a 
challenge in breeding for resistance.  
27 
 
 
Resistance to Ralstonia solanacearum has been reported in some tomato 
genotype but incorporation of resistance into materials with good horticultural 
charactersistics has been difficult (Peregrine, 1982; Peterson et al., 1983). 
Ralstonia solanacearum strain type, genetic variability of the plant and 
reproducibility of the inoculation technique may affect the selection of 
resistant material (Prior et al., 1990a). Some Ralstonia solanacearum resistant 
cultivars have been developed at the Asian Vegetable Research and 
Development Center (AVRDC). However, their resistance is restricted to 
climate, locations and strains of the pathogen and soil characteristics 
(AVRDC, 2003). A number of tomato varieties have been developed with 
significant levels of resistance for certain environments (Gomes et al., 1998); 
in a number of cases the stability in regions with high temperatures and 
humidity especially in lowland tropics is difficult to achieve as resistance 
breaks when variety is transferred to a different region (Hayward et al., 1991; 
Hanson et al.,1996). 
2.5 Grafting 
Grafting is a vegetative plant  propagation procedure in which  plant parts are 
joined together with the ultimate intention of uniting them and continue 
growing as one plant (Bareja, 2011). The rootstock is the base portion of the 
union that provides the root system while the scion is the upper part that 
carries the harvestable yield (Genova et al., 2013). 
In horticulture, grafting is widely used for a variety of reasons. Dwarfing 
rootstock are used to control the size and vigor of the tree, especially in fruit 
trees like apple. Grafting can be very effective against a variety of soil-borne 
28 
 
 
viral, bacterial, fungal and nematode diseases and can also be an alternative 
technique to using methyl bromide, a chemical fumigant to control soil- borne 
diseases.  
Grafting has allowed not only production of high quality fruit but also for 
resistance to many infectious diseases (McAvoy, 2005). It is also an 
alternative crop management strategy to control bacterial wilt when high – 
yielding resistant varieties are unavailable (Wang and Lin, 2005). Field studies 
also show that grafting is one of the most promising options in stemming the 
impact of bacterial wilt on tomato production as well as increasing the overall 
productivity of tomato cultivars (Taylor et al., 2011, Rivard eta al., 2012). 
Rootstocks used in grafting can also provide a stronger and more cold-hardy 
or heat-resistant root system. They can also increase fruit size, yield and 
quality of the tomato. Grafting is used to increase resistance to soil-borne 
diseases especially with field grown vegetables. Tomato growers graft 
tomatoes onto eggplant rootstocks to increase resistance to flooding and 
bacterial wilt disease resulting in higher yield and economic returns (Palada 
and Wu, 2005). 
Grafting applies to the gymnosperms and the dicots because vascular cambium 
is continuously present between the xylem and the phloem. However, 
successful grafts are rare and difficult in the monocots that have no vascular 
cambium. The rootstock is the lower part having roots and a stem that is to 
become the lowermost part of the shoot of the grafted plant and provides 
anchorage and support to the upper parts of the plant. Selected rootstock 
29 
 
 
should be resistant to soil borne pests and diseases, should belong to the same 
family as the scion and should be compatible with the scion to be grafted on. 
The scion is the upper part that is joined to the rootstock and the main 
component of the plant shoot when the plant is fully developed. The scion also 
determines the characteristics of the plant as to leaves, flowers, fruits and 
seeds, and thus needs to be chosen with care (Bareja, 2011).  
Desirable scions can be grafted on rootstocks that are adapted to certain 
conditions such as heavy, wet, or dry soils, or resistant to soil borne pests and 
diseases. The compatibility of the rootstock and scion that leads to successful 
union depends on how close they are in their taxonomic classification. The 
scion and the rootstock may not germinate at the same rate, therefore, seeds 
for both the scion and the rootstock cultivars should be seeded so that they are 
ready for grafting in 14 -21 days or when tomatoes have attained 2 - 4 true 
leaves (Sacha, 2011). During grafting, the rootstock and the scion are cut at an 
angle of 45 – degree above the cotyledon to ensure that the rootstock and the 
scion stem are of similar diameter (Maribel and Paul, 2010). 
 For successful graft union to form, the rootstock and the scion cambium must 
be well aligned and in contact with one another because if the diameter does 
not match, the graft takes longer to heal and the rootstock can slowly starve to 
death (McAvoy, 2005). The scion and the rootstock plants must therefore have 
the same stem diameters at the time of grafting and they are both watered 12-
24 hours before grafting (Sacha, 2011). In other parts of the world grafting has 
been done to increase tomato production. For example, in the Philiphines, 
30 
 
 
tomato production is limited during the hot – wet months because of flooding, 
high temperatures and occurrence of pests and diseases. Therefore, tomato 
grafting onto flood and disease resistant rootstock was a potential technology 
to overcome these abiotic and biotic problems (Aganon et al., 2004).  
In Kenya, trials on grafting were carried out in a participatory research activity 
with Kangai Tisa Farmers group in Kirinyaga County using wilt resistant 
rootstock of Mt56 (Waiganjo et al., 2011). Among the un-grafted tomato lines, 
bacterial wilt severely infected both determinate and indeterminate tomatoes 
grown in high tunnels and open fields and results indicated that grafting 
bacterial wilt susceptible variety such as the Onyx on resistant Mt56 resulted 
in significantly less disease incidence in high tunnel (15%) and open field 
(25%) (Waiganjo et al., 2011). 
2.5.1  Grafting in bacterial wilt management 
Use of resistant rootstocks provides a more stable strategy in management of 
bacterial wilt but performance varies with temperature and location (Wang et 
al., 1998). Abdullah (1998) found that  susceptibility of six tomato cultivars to 
bacterial wilt differed significantly indicating that the additive genes were 
more important than the non- additive genes. Grafting susceptible tomato 
cultivars onto resistant tomato or other solanaceous rootstock has recorded 
high control against Asian strains of Ralstonia solanacearum and this 
technology has been used in many parts of the world (Black et al., 2003; 
Saddler, 2005). The use of grafted transplants has historically been effective 
for managing bacterial wilt in the field worldwide although it has been 
31 
 
 
difficult to integrate resistance genes into modern tomato cultivars. A recent 
study used two open-pollinated tomato-breeding lines, ‘CRA 66’ and ‘Hawaii 
7996’, as rootstocks for field production of heirloom tomatoes and reported no 
disease incidence in plants grafted to either rootstock, whereas non-grafted 
and self-grafted entries exhibited 50 to 80% incidence (Rivard and Louws, 
2008). 
 In India and Germany, CRA 66 has been identified as a resistant rootstock 
variety for grafted tomato production (Grimault and Prior, 1994). Graft of 
susceptile cultivars of tomato on resistant rootstocks belonging to Solanum spp 
has been reported to be effective in management of bacterial wilt (Gupta and 
Thind, 2006). Grafting experiments have indicated that the wilting percentage 
of scions from Penderosa was less on Hawaii 7996 rootstsocks than that on the 
most resistant rootstock (LS - 89) used in Japan. Hawaii 7996 could be an 
alternative genetic source for breeding for resistance to Bacterial wilt (Nakaho 
et al., 2004). Use of grafting technique provides new possibilities as resistant 
rootstocks can be grafted with widely grown commercial tomato varieties 
(Taylor et al., 2011). In future Ralstonia solanacearum management with 
resistant rootstocks will offer the most economic and more sustainable 
solution to the pathogen (Wang, 2005 ; Mbaka et al., 2013).  
2.5.2 Compatibility of scion and rootstock in grafting 
Graft compatibility is the establishment of a successful graft union as well as 
extended survival and proper functioning of the composite, grafted plant. 
Taxonomic affinity is a prerequisite for graft compatibility. Homografts 
32 
 
 
(autografts) are presumably always compatible (Mudge et al., 2009). In 
rootstock and scion belonging to the same botanical species (heterografts, 
intraspecific grafts) are nearly always compatible, rootstock and scion 
belonging to different species of the same genus (interspecific grafts) are 
usually compatible, interfamilial grafts are essentially always incompatible 
and intrafamilial grafts are rarely compatible (Mudge et al., 2009). 
Heterografts compatibility examination should include homograft controls 
(Olmstead et al., 2006; Flaishman et al., 2008; Kawaguchi et al., 2008), a 
requirement not always fulfilled (Guan et al., 2012). Certain grafting effects 
are evident even in homografts, where rootstock and scion share the same 
genetic background.  
MicroRNA (miRNA) expression patterns and reproductive development of 
rootstock and scion is markedly affected by differences in rootstock and scion 
age and juvenility (Poethig, 2009; Wang et al., 2011). Grafts of old-stage have 
xylem connections of lower percentage and suffer drought stress (Johkan et 
al., 2009). 
Graft incompatibility is the failure to form a successful graft union. Long-term 
compatibility is not in itself ensured by the initial healing of the graft union. In 
cucurbits, apparently successful grafts proved incompatible 25 days after 
grafting (Edelstein et al., 2004; Aloni et al., 2008). Although incompatibility 
is not a measurable quantitative trait, various degrees of incompatibility may 
be discerned, from mild interference with the normal development of the 
composite plant to mortality of the stock, scion or both. As already pointed out 
by Moore (1984), as yet there is no evidence for a specific biochemical-
33 
 
 
immunological recognition/rejection mechanism between the graft 
components.Genetic distance increases heterograft incompatibility (Flaishman 
et al., 2008), indicating some kind of physiological rejection. In a rather 
unpredictable fashion, incompatibility occurs even among related genera of 
the same family. Thus, within the Solanaceae, reciprocal grafts of tomato 
(Solanum lycopersicom L.) and pepper were considered severely incompatible, 
whereas tomato and eggplant (Solanum melongena) only moderately so, in 
comparison with compatible tomato homografts (Kawaguchi et al., 2008). 
2.5.3 Grafting methods 
In vegetable crops, a variety of grafting methods can be used. Tongue grafting 
involves notching opposing sides of the stems of the rootstock and scion, and 
then using a clip to hold the stems together while they fuse. Once the graft has 
healed, the original scion is then cut off of the desired rootstock and the 
unused rootstock is detached from the scion (Lee, 1994). Cleft grafting occurs 
when a V-shape is cut into the rootstock and a complementing wedge-shaped 
scion is inserted. The graft is then held with a small clip until healing occurs 
(Oda, 1999). Micrografting is a new technique that has been recently 
integrated into micropropagation production for hybrid tomato. This method 
uses micropropagated scion shoots that is grafted onto 3 week - old rootstock 
seedlings (Grigoriadis et al., 2005). Tube grafting is the most common 
commercial technique for grafting tomato. Tube grafting takes place when the 
rootstock and scion are severed as seedlings and reattached with a small, 
silicon tube or clip (Oda, 1995). This technique can be carried out when plants 
34 
 
 
are very small and has been highly effective, thereby eliminating the need for 
large healing chambers while increasing throughput. The primary method that 
has been adopted for vegetable grafting on the farm is tube grafting as it can 
be easily carried out with typical success rates ranging from 85 to 90 percent 
in small healing chambers (Oda, 1995). 
2.5.4 Physiological aspects of rootstock–scion interaction 
Water and nutrient uptake could be increased in grafted plants as a result of 
the enhanced vigour by the rootstock root system and its effects on plant yield 
(Ruiz et al., 1997). Thus, water relations in the rootstock – scion system, as 
well as the influence of the graft union on water transport to the aerial parts, 
have been studied with special emphasis on the search for plants able to 
withstand environmental changes. Plants form callus at the graft interface, 
which enables water to flow from the rootstock to the scion when the callus 
develops vascular bundles (Moore, 1984a,b). Water flow between the scion 
and the rootstock decreases when there is insufficient connection of vascular 
bundles (Torii et al., 1992).  
Stomatal conductance and scion growth decreased when water absorption by 
roots was suppressed at the graft interface (Atkinson and Else, 2001; Oda et 
al., 2005). Thus, hydraulic architecture becomes of fundamental importance, 
since the sustained flow of water controls many plant processes such as 
mineral nutrition, photosynthesis, transpiration and growth. Graft 
incompatibility can induce undergrowth or overgrowth of the scion, which can 
35 
 
 
lead to decreased water and nutrient flow through the graft union and cause 
wilting of the plant (Davis et al., 2008).  
Grafting incompatibility usually occurs at early stages, when vascular 
connections are forming, but it can appear as late as the fruiting stage,  when 
the plant has a high demand for water and nutrients. It has been reported that 
the supply of warm water to the graft union of grafted tomato and eggplant 
plants improved the storage quality, reducing water stress at the beginning of 
the storage when vascular tissues of the rootstock and scion are not connected 
yet (Tokuda et al., 2006; Shibuya et al., 2007). This reduction of water stress 
by a high graft union temperature was due to improved water absorption by 
the scion (Shibuya et al., 2007). The promotion of root development and 
improved management of watering are important in grafted plants so as to 
avoid physiological wilt. 
The stage of the plant at the moment of grafting is important with respect to 
the efficiency of the rootstock–scion interaction. Thus, sweet pepper plants 
grafted when older showed poor development in their xylem connections at 
the graft site, which resulted in low stomatal resistance and water potential 
compared to younger plants (Johkan et al., 2009). The effects of the rootstock 
genotype on the graft union and scion water relations were marked in grafted 
melon plants (Agele and Cohen, 2009). Leaf water content was increased by 
35% in grafted plants with an includer character scion than in self-grafted 
plants (Santa-Cruz et al., 2002). In several graft combinations of tomato, leaf 
water content was similar under control conditions but increased to different 
36 
 
 
levels with salinity making specific grafting combinations more resistant to 
salinity (Martínez-Rodríguez et al., 2008). In a similar way, under water 
deficit, the leaves of grafted tomato plants maintained higher leaf water 
potential than self-grafted plants in spite of higher water loss through 
transpiration, indicating a greater ability to promote water uptake (Weng, 
2000). 
2.5.5 Hormonal aspects of rootstock–scion interactions 
The success of grafting depends primarily on the identification of stress and 
pathogen - resistant rootstock and on the compatibility of the graft union in 
terms of fast formation of the vascular connections between the rootstock and 
the scion and fast renewal of root and canopy growth (Cohen et al., 2007). In 
grafted plants, the vascular regeneration is re - established by complex 
processes, which include structural differentiation of the parenchymatous 
tissue from both sides of the graft union into xylem and phloem tubes. 
Vascular development includes formation of the longitudinal pattern of 
primary vascular strands, formation of the radial pattern of xylem and phloem 
within vascular strands, differentiation of specialized cell types from xylem 
and phloem precursors and cell proliferation and cell differentiation within the 
vascular cambium (Dengler, 2001). Vascular regeneration experiments in 
which hormones were applied exogenously to stem segments indicated that 
low concentrations (0.1%, w/w, applied in lanolin) of indole acetic acid (IAA) 
stimulate phloem differentiation, whereas higher levels (1.0%, w/w) induced 
xylem differentiation (Aloni, 1980, 1987, 1995, 2001). In grafting, an 
37 
 
 
important substance involved in the development of compatible graft union is 
auxin, which is released from vascular strands of the stock and the scion and 
induces the differentiation of vascular tissues, functioning as morphogenic 
substances (Aloni, 1987; Mattsson et al., 2003). Auxin translocation from the 
scion to the rootstock was found to accelerate the formation of a successful 
graft in Cactus (Shimomura and Fujihara, 1977). 
2.5.6 Healing Process 
Meristematic tissue must develop into vascular tissue that will reconnect the 
scion and rootstock during the healing process. An experiment that used a non 
- destructive method to assess the development of hydraulic connections in the 
graft union of tomato showed that the graft union is completely functional 6 - 
8 days after grafting (Turquois and Malone 1996). The early stage begins 
within 4 days, and is characterized by the death of cell layers at the graft 
interface as a result of wounding. The gap between the rootstock and the scion 
is filled by generation of parenchymatous callus tissue, and living cells from 
the surface quickly begin to grow in size and divide. Differentiation of callus 
parenchyma into new cambial tissue occurs, and the subsequent union of the 
newly formed vascular strand with the original vascular bundle in both the 
rootstock and the scion begins between days 4 and 8. After 15 days, this 
differentiation and union formation process is fully developed (Fernandez-
Garcia et al., 2004). Peroxidase activity during the graft union formation and 
development, and enzyme plays a major role in lignification of xylem vessels 
(Fernandez-Garcia et al., 2004). 
38 
 
 
2.6 Potential sources of rootstocks for grafting tomato 
2.6.1 Capsicum 
Capsicum (Capsicum annuum) belongs to the family Solanaceae as are 
potatoes, tomatoes and egg plants (Faisal et al., 2013). Capsicums are a hardy 
type of plant that is moderately attacked by diseases and pests. Capsicum is of 
various cultivars which include Green pepper, Sweet pepper, Chilies and 
pepper (Burt, 2005). Research showed that grafting capsicum could be used as 
an alternative control method of soil-borne pathogens such as Phytophthora 
nicotianae (Mahmoud et al., 2010).  
2.6.2 Eggplant 
Eggplant (Solanum melongena) is a member of the Solanaceae family and is 
botanically related to pepper, potato and tomato. To help them tolerate dry 
weather, they  have a deep taproot. Eggplant is normally propagated by seed 
and propagation by rooting of healthy shoots is also possible. Varieties of 
Solanum melongena available locally include Black Beauty, Ravaya, Long 
Purple and Early Long Purple. Solanum melongena is known to be resistant to 
bacterial wilt, floods and root – knot nematodes and is recommended by 
AVRDC for use in tomato grafting (Black et al., 2003). 
2.6.3 Sodom Apple 
Sodom apple (Solanum incarnum L.) is a member of Solanaceae family and 
thought to originate in Africa and also found from the Middle East to India 
(Lusweti et al., 2011). Solanum incarnum is a weed of overgrazed, disturbed 
39 
 
 
areas and road sides but also found in various types of woodland, and along 
the margins of riverine and evergreen forest (Lusweti et al., 2011). Research 
has been done and the result showed that S. incarnum is resistant/tolerant to 
bacterial wilt (Magambo et al., 2002) and is therefore a suitable candidate for 
use in grafting. 
2.6.4 Resistant tomato cultivar 
The tomato variety Mt56 has been reported to exhibit resistance to the 
bacterial wilt pathogen. This variety was introduced from Ohio Agricultural 
Research and Development Center (OARDC) breeding programme to Uganda 
and the cultivar had been observed to be moderately resistant to R. 
solanacearum in Uganda (Karungi et al., 2011). Mt56 is not being grown for 
direct sale because it does not meet the market demand in terms of  quality and 
size. Ongoing research by KALRO is aimed at confirming the resistance of the 
variety (Karungi et al., 2011). In Kenya, the trial results indicated that grafting 
bacterial wilt susceptible variety (Onyx) on Mt56 resulted in significantly less 
disease incidence both in open field and high tunnel (Waiganjo et al., 2011). 
 
 
 
 
 
 
 
 
40 
 
 
CHAPTER THREE: MATERIALS AND METHODS 
 
3.1 Survey  
3.1.1 Survey site 
The study commenced with a survey in Kirinyaga county, Mwea East sub – 
county to determine the important pests, pathogens, tomato varieties grown in 
the region, seed systems for tomato and other key tomato production 
constraints. Kirinyaga County was selected for the study because it has the 
highest tomato production in Kenya (HCDA, 2013), has high incidence of 
bacterial wilt (Mbaka et al., 2013) and had been used as a site in a previous 
related research (Onduso, 2014), therefore had higher potential to adopt 
technologies developed. Within Kirinyaga County, three locations; were 
randomly selected in Mwea East (Tebere, Nyangati and Murinduko) (Figure 
2). The three locations were selected because of their history in tomato 
production, bacterial wilt incidence and availability of irrigation water from 
canals. Kirinyaga County is located in the central part of Kenya and borders 
Murang’a County in the West and Embu County to the East. The County is 
located between latitudes 0o  1”  and 0o 40”S and longitudes 37o and 38o. The 
area  receives bi-modal rains ranging from 1,100mm to 1250mm per year with 
long rains occurring between March and May while the short rains fall 
between October and November. The farmers depend on rains for crop 
production during rainy season and irrigation during the dry season. 
Temperatures range between 12 – 26oC. 
41 
 
 
The county has deep and moderately fertile volcanic soils with good water 
holding capacity. Farmers in the county undertake tomato farming for 
domestic market and consumption with the greatest percentage grown for 
income generation. 
 
Figure 2: Kirinyaga County map showing locations of  survey 
(Murinduko, Nyangati and Tebere) in blue arrows 
 
 
42 
 
 
3.1.2 Survey data collection 
A sample of 100 farmers were selected in the study area. The sample size for 
the study area was determined using the formular; 
n = NC2 / C2 + (N-1)e2 
Where, n =Sample size, N= Population size (100 farmers), C= Coefficient of 
variation which is <30% and e= Margin of error which is fixed between 2-5% 
(Nassiuma, 2000). The farms in the three locations were selected and  
interviews purposefuly conducted with individuals who were active tomato 
producers or had been engaged in production of tomato for the past six 
months. County extension officers and KALRO – Mwea staff  helped to 
identify the survey areas and farmers. The required information was obtained 
from researchers at KALRO – Mwea and farmers using a structured 
questionnaire (Appendix 1) administered to each respondent during farm visit. 
Further information was obtained through direct observation during a transect 
walk through each farm that was surveyed. Presence of pests, disease 
incidence and severity levels were recorded. A photo card (Appendix 2) was 
used to aid  the farmers in description of the diseases and pests. Farm 
management in terms of agronomic practices such as weeding, sanitation 
(removal of infected plants), manure application and watering among others 
were rated using a scale of 1 (poor) -5 (good). Samples of diseased plant 
tissues were taken to the laboratory for isolation of R. solanacearum. 
 
43 
 
 
3.2 Grafting experiments  
3.2.1 Experimental site 
The grafting experiment was conducted in a greenhouse at Kenyatta 
University Research and Teaching Farm. A maximum and minimum 
thermometer was used to record the temperatures within and outside the 
greenhouse; in addition relative humidity was monitored. Temperatures 
outside the greenhouse varied from 23oC to 28oC. 
3.3  Selection of plants for use as scion and rootstocks 
The criteria for selecting the rootstocks was based on botanical relationship to 
tomato (Solanaceae family) and using available literature. Candidate species 
included, Solanum incarnum (Sodom apple), tomato variety Mt56, Capsicum 
(Capsicum annuum sp L) and Solanum melongena (Eggplant). The tomato, 
capsicum and eggplant seeds were obtained from Kenya Seed Company Ltd in 
Nairobi whereas Sodom apple was obtained from the bush. The scion species 
(Anna F1) seeds from Monsanto Kenya Limited, Nairobi and Cal J seeds from 
East Africa Seed Co. Ltd. also in Nairobi were obtained from local agrovet 
shops. Anna F1 and Cal J were selected for this research due to their high 
market demand despite susceptibility to bacterial wilt. Anna F1 is an 
indeterminate fresh market variety that performs best when grown in green 
houses and matures relatively fast within 75 days after transplanting but 
maturity period depends on the weather. It has high yields and has firm, oval 
shaped fruits that are deep – red in color. Anna F1 is also preferred in Kenya 
as it is resistant to Alternaria stem canker (Alternaria alternata f.sp. 
44 
 
 
lycopersici), nematodes and Fusarium wilt which are common constraints. Cal 
J is a determinate tomato variety that matures in 70 -80 days. Its tolerant to 
most common diseases and it is high yielding. 
3.4 Establishment of seedlings  for scion and rootstock in the nursery 
Seedlings of each of the selected rootstock and scion candidate species were 
raised on well prepared nursery beds. The rootstock seeds were planted 5 – 7 
days earlier than the scion. These were raised for one month or more 
depending on the growth rate of the plant, plant type and whether the plant 
was used as a scion or rootstock. Transplanting was done in polybags of 
dimensions 9cm by 5cm by 10cm in sterile media of soil and manure after 
three weeks in the nursery (Plate 1). 
    
Plate 1: Rootstock seedlings transplanted in polybags 
 
3.5  Isolation of Ralstonia solanacearum and preparation of inoculum 
3.5.1 Sample Selection 
Isolates of R. solanacearum were obtained from fresh symptomatic plants 
obtained from naturally infected plants of variety Kilele in farmers’ fields in 
45 
 
 
Mwea (Kirinyaga County). The fresh symptomatic plants were cut into pieces 
of 10 cm in length and cleaned using running tap water to remove debris and 
soil particles. Sterile distilled water in conical flasks was autoclaved for 
sterilization for 15 minutes at 121oC.  
The infected stems were sterilized in 70% ethanol and then rinsed with sterile 
distilled water. The stem portions were  suspended in the sterile distilled water 
for observation of bacterial ooze (Plate 2). 
         Bacterial ooze 
Plate 2: Infected tomato stem with bacteria oozing into distilled water 
3.5.2 Media preparation 
Selective medium for R. solanacearum isolation was prepared using Casamino 
acid – peptone - Glucose (CPG) medium as described by Allen et al. (2008) 
consisting of Casamino acid (casein hydrolysate) -1.0g per litre, Peptone – 10g 
per litre, Glucose – 5g per litre and agar 17.0g per litre. The solution was 
auotoclaved for 15 minutes at 121oC, pH was adjusted to 6.5 – 7.0 and the 
46 
 
 
medium was then allowed to cool; Tetrazolium Chloride (TZC) was added in 
the media to identify pure colonies of R. solanacearum.  
3.5.3 Isolation of R. solanacearum colonies 
Colonies of R. solanacearum were usually visible after 48 hours of incubation 
at 28oC. Colonies of the normal (virulent type) were pink colored, irregularly- 
round, fluidal and opaque (Allen et al., 2008), (Plate 3a). Sub- culturing was 
done to get pure cultures which were used to make the  inoculum used on 
experimental plants (Plate 3b). 
                  
Plate 3: Isolated colonies of R. solanacearum in TZC Media (a) (F – non-
virulent and G – virulent colonies) and Sub- cultured colonies of R. 
solacearum (b) 
3.5.4 Inoculation of plants with R. solanacearum 
Three weeks after transplanting and when the  plants had attained 2-3 leaves, 
innoculation was done by drenching the potting media with the R. 
solanacearum suspension of 1.2 x 108 cfu/ml (Prior et al.,1998). The control  
plants had their potting media drenched with sterile water. The scoring scale 
for disease severity was 0 - 5; with 0 indicating all inoculated plants had no 
47 
 
 
disease while 5 indicating  all inoculated plants had 100% infection and are 
therefore susceptible. 
Pests and diseases were controlled using pesticides such as Imidacloprid 
(against whiteflies, thrips and aphids) and fungicides such as Metalaxy l - M + 
Mancozeb (against blight and powderly mildew). Standard agronomic 
practices for tomato production were deployed and included; watering which 
was done three times a week and crop nutrition. NPK 23:23:0 (10gms per hole 
or 50 kgs/ha) were applied during transplanting, NPK 17:17:17 (10gms per 
hole or 50 kgs/ha) used as top dressing fertilizer one month after transplanting 
and foliar fertilizers such as Boomflower (Nitrobenzene) (1ml/ litre of water) 
at flowering, Easygrow and Calcium Nitrate both used as foliar fertilizers 
(40gms/20litres of water).  
3.5.5 Observations and Data recording 
Inoculated plants were observed daily until appearance of the first wilt 
symptoms. Data on disease incidence were recorded based on the number of 
plants showing wilting symptoms. The rootstock candidate cultivars that did 
not show susceptibility to bacterial wilt after inoculation with R. 
solanacearum were selected for further evaluation when grafted to susceptible 
tomato cultivars Anna F1 and Cal J. 
 
 
48 
 
 
 
 
          
 
Plate 4: Wilted plant (a) and vascular discoloration (b) of Capsicum plant 
after inoculation with R. solanacearum 
3.6 Determination of the compatibility of bacterial wilt resistant 
rootstocks to preferred tomato cultivars 
3.6.1 Raising of seedlings 
The seedlings of rootstocks and the scions were raised in the nursery and 
transplanted in polybags as described in section 3.4 above. They were then 
screened for bacterial wilt resistance to identify the resistant germplasm for 
grafting with susceptible tomato cultivars as described in section 3.5.1 above. 
Selected resistant rootstocks were tested for compatibility with tomato 
cultivars Anna F1 and Cal J. The rootstocks and scions seedlings were cut 
cleanly between the cotyledon (above) and true leaves (below) to reduce the 
likelihood of shoots (suckers) developing from the rootstock. Seedlings were 
grafted before they became woody at 2 - 3 true leaves growth stage ( Sacha et 
al., 2011). 
a b 
49 
 
 
3.6.2 Grafting of the susceptible scions onto selected resistant rootstock 
Grafting was done when the resistant rootstocks were one month old and had 
attained  2 -3 true leaves and the cambium layer had not hardened. During the 
time of grafting the scions were three weeks old. Grafting was done under 
shade netting of 90% density. All the ten replicates were grafted on the same 
day. To increase the likelihood of the herbaceous scion and rootstock coming 
into contact, the exposed area was maximized by cutting the scion and 
rootstock at a 45- degree angle during grafting. The cleft grafting method was 
used and grafting tapes were used to firmly hold the rootstock and the scion 
together.  At 14 days after grafting, the number of grafted plants that were 
fully healed and had ‘taken’ were recorded. Rootstocks with a minimum of 
two thirds of the grafted plants surviving were considered compatible and 
selected for the next experiment to assess their effectiveness in reducing 
infection by R. solanacearum. 
3.7 Evaluating resistance of grafted seedlings to bacterial wilt 
Rootstocks selected as described in section 3.3 above and grafted as described 
in section 3.6.2 above were inoculated by drenching the soil with R. 
solanacearum suspension as described in section 3.5.4. The grafted inoculated 
seedlings were incubated in the green house, watered, fed and protected 
against pests and diseases by use of insecticides and fungicides. The 
incubation period for the disease was two weeks. Data on disease incidence 
was recorded for twenty one days. 
50 
 
 
3.8 Evaluating the effect of plant growth stage on grafting practices  
Scions and rootstocks were grafted at two growth stages, namely young (2 - 3 
leaf stage) and old (4 - 5 leaf stage) stages to determine the appropriate stage 
of grafting. The grafted plants were then kept in the green house where 
temperature was monitored using a maximum and minimum thermometer and 
watering done three days a week. Data on the number of the grafted plants that 
successfully established and the grafted plants that did not establish 
successfully for each variety were recorded after two weeks. 
4.0 Experimental design and Data analysis 
The experimental design was a Completely Randomized Design (CRD) with 
ten replicates. Data was subjected to Analysis of Variance (ANOVA) using 
Genstat. Significantly different treatment means were separated using LSD at 
p<0.05. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
51 
 
 
CHAPTER FOUR:  RESULTS 
 
4.1 Survey Results 
Of the targeted 100 farmers in Mwea East, a higher proportion was sampled in 
Tebere location (45%), Nyangati (37%) and Murinduko (18%). 
From the survey results, the highest proportion engaged in tomato production 
is male (70%) and female (30%). However, based on age category by gender, 
more males aged between 36 –50 years (52.9%) were involved in tomato 
production compared to 60% of females aged between 18 – 35 year. 
4..1.1 Variety of tomatoes grown by farmers  
Kilele F1 was the most commonly grown variety (46.2.%), followed by 
Rambo F1 at 32.1% and Riograde at 15.2 % (Figure 3). Production of Anna 
F1 (1.8%) and Cal J (0.9%) which were popular in the past in the area had 
declined significantly due to bacterial wilt. 
 
 
 
52 
 
 
 
Figure 3: Respondents (n=100) growing different types of tomato varieties 
in Mwea East Sub-County 
 
Kilele F1 was grown in a larger acreage followed by Rambo F1 (Figure 4). 
The land acreage is important in the management of bacterial wilt because 
larger land size enable crop rotation which is a way of managing Ralstonia 
solanacearum. 
 
Figure 4: Area of tomato production grown by farmers in Mwea East Sub 
county 
53 
 
 
4.1.2 Source of planting materials 
The farmers in Mwea East bought seeds from agro-shops or agronomists of 
various companies. Most farmers (43.4%) would then make their own 
nurseries and grow their own seedlings, this also included farmers who 
extracted seeds from fruits (43.4%); farmers who bought seedlings from local 
nurseries were very few at 13.1% (Figure 5). Farmers experienced varous 
challenges in the raising of seedling with the greatest challenge being damping 
off (37.7%), low seed viability (30.8%), poor seedling vigor (23.9%) and lack 
of trueness to type (7.5%). 
 
Figure 5: Source of tomato planting materials used by farmers in Mwea 
East Sub - county 
4.1.3 Tomato Production challenges 
Farmers experienced various problems during tomato production. The main 
challenges were pests and diseases such as Early Blight (Alternaria solani)  
(97%), Bacterial wilt (Ralstonia solanacearum) (91%), Late blight 
54 
 
 
(Phytophthora infestans) (80%), Tomato curl yellow leaf (TYLC) (48%), 
Verticillium wilt (Verticillium albo-atrum) (43%), Powderly mildew 
(Oidiopsis sicula) (45%), Bacterial spot (Xanthomonas campestris pv. 
Vesicatoria) (44%), Septoria leaf spot (40%), Stem canker (28%), Bacterial 
pith necrosis (Pseudomonas corruga) (28%) and Grey mold (Botrytis cinerea) 
(27%). Early blight (Alternaria solani) was the most common disease 
followed by bacterial wilt (Ralstonia solanacearum) and late blight 
(Phytophthora infestans) while the least common was Bacterial speck 
(Pseudomonas syringae pv. tomato) (Figure 6).  
Bacterial wilt was noted to be the most severe disease because it did not 
respond to the management strategies that were applied and caused the 
greatest loss to the farmers. 
 
Figure 6: Tomato diseases experienced by tomato farmers in Mwea East 
Among the pests mentioned by farmers, sucking pests were most prevalent. 
These included white flies (21.9%),  thrips  (19.4%), Red spider mites (18.7%) 
and aphids (5.5%). The major galling pests affecting the farmers was 
55 
 
 
nematodes (17.6%); the leaf miner pest (Tuta absoluta) was significantly high 
(16.9%) ( Figure 7).  
 
 
Figure 7: Pests affecting tomato farmers in Mwea East sub county 
Various fungicides were used in the control of diseases in the study area. The 
most commonly used fungicide was Metalaxl –M (25.6%) followed by 
Cymoxanil (ethylurea) 60g/kg;Propineb (dithiocarbamate) 700g/kg(12.6%) (Figure 
8), both were used in control of both early and late blight. Few farmers (7.7%) 
attempted to use Copper hydroxide 50% to control Bacterial wilt disease but this 
was ineffective (Figure 8). The active ingriedients of various fungicides used 
are as indicated in Table 2. 
56 
 
 
 
Figure 8: Common fungicides used in tomato production in Mwea East 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
57 
 
 
Table 2: Some of the common fungicides and their Active ingredients 
used in tomato production in Mwea East 
Trade name Active ingredient Target pathogen Effectiveness 
(as rated by 
farmers) 
RindomilGold Metalaxl –M Oomycetes fungi Highly Effective 
Milraz 76 WP Cymoxanil(ethylurea) 
60g/kg; Propineb 
(dithiocarbamate) 700g/kg 
Late blight 
(Phytophthora 
infestans) 
Effective 
Oshothane 
80WP 
80% Mancozeb Down mildew, early 
blight, late blight, 
Anthracnose, leaf 
spot 
Effective 
Funguran–OH 
50WP 
Copper hydroxide 50% Fungal Moderately 
effective 
Milthane 
Super 
Mancozeb Downy mildew, Early 
blight, late blight 
Moderately 
effective 
Mistress 72 
WP 
Cymoxanil 8% + Mancozeb 
64% 
Early blight, Late 
blight 
Less effective 
Antracol(R)70 
WP 
Propineb 700g/kg Early blight, late 
blight, grey leaf spot 
Less effective 
Victory 72 
WP 
Metalaxyl 80g/kg + 
Mancozeb 640g/kg 
Fungal Less effective 
Agromax Cymoxanil 8% + Mancozeb 
64% 
Early blight, Late 
blight 
Less effective 
Infinito 687.5 
SC 
Fluopicolide 
65.2g/kg+Propamocarb 
hydrochloride 625g/kg 
Downy mildew, late 
blight 
Lesseffective 
Mancozeb Dithiocarbamate Early blight, late 
blight, Anthracnose, 
leaf mold, Septoria 
leaf spot 
Least effective 
 
58 
 
 
Chlorantraniliprole 18.5% was the most widely used insecticide (31.3 %) 
targeting Tuta absoluta. Lamdacyhalothrin and Emamectin Benzoate were also 
commonly used by 13.8 and 10.0% of respondents, respectively, in the control 
of white flies (Figure 9). The active ingriedients (Table 3) are as indicated. 
 
Figure 9: Common insecticides used in tomato production in Mwea East 
 
 
 
59 
 
 
Table 3: Insecticides and their Active ingredients commonly used in 
tomato production  
Trade 
name 
Active Ingredient Target pest Effectiveness 
Coragen Chlorantraniliprole 
18.5% 
Tomato Fruit borer, Tuta 
absoluta 
Highly effective 
Thunder 
2.5 EC 
Lamdacyhalothrin White flies  Effective 
Prove 
1.92EC 
Emamectin 
Benzoate 
Caterpillars, Thrips Effcetive 
Dynamec 1.8% Abamectin Leaf miner, Mites Effective 
Belt 480 
SC 
Flubendiamide DBM, Caterpillars Moderately effective 
Escort 19 
EC 
Emamectin 
Benzoate 19g/L 
Thrips, Spider mites, 
Caterpillars 
Moderately effective 
Swift   Moderately effective 
Levo 2.4SL Prosuler Oxymatrine 
2.4% 
Thrips, Mites, 
Caterpillars 
Least effective 
Confidor Imidacloprid White flies, Aphids, 
Thrips, Caterpillars 
Least effective 
Tata Alpha Alpha – 
cypermethrin 
Aphids, Whiteflies, 
Thrips,  Caterpillars 
Least effective 
 
4.1.4 Crop Management Strategy 
Use of organic and inorganic fertilizers was reported in tomato production 
with organic fertilizers being much more commonly used (62.5%) than the 
inorganic fertilizers.  
60 
 
 
Crop rotation was practiced by tomato farmers in Mwea East sub-county with 
maize being used as a rotational crop by majority of the farmers (78.0%), 
followed by beans (16.3%) and Kales (5.7%).  
Various ways of managing tomato remains in the farms such as burning the 
remains in the farm, throwing them away, burying in the soil and others 
feeding to the livestock were practiced. The most common practice was 
burning the residues (44.4%) followed by throwing the residue away (25 %), 
burying in the soil (23.2%) and  feeding the livestock (7.1%). 
Watering was ranked as the practice done by the farmers because all the 
farmers used rivers and canals for irrigation. (Figure 10) followed by plant 
protection measures and then weeding which was manually done while the 
poorly done agronomic and farm management practices was desuckering and 
removal of the infected plants (Figure 10). Failure to remove the infected 
plants encouraged the spread of Ralstonia solanacearum. 
 
Figure 10: Assessment of agronomic and crop management practices on 
tomato production in Mwea East sub county 
61 
 
 
Disease presence was observed during the survey with bacterial wilt noted to  
be highly prevalent (31.4%) followed by Early blight and late blight with a 
proportion of 26 and 20.4% respectively. Tomato mosaic virus and brown spot 
(Xanthomonas campestris pv.vesicatoria) were ranked the least common 
disease in tomato production (Figure 11). 
Figure 11: Diseases prevalence in tomato plants during survey in Mwea 
East Sub - County 
4.2 Identification of bacterial wilt resistant germplasm for use as 
rootstocks 
Solanum melongena, Solanum incarnum and tomato Mt56 were not infected 
and thus were classified resistant/tolerant. For the susceptible controls (Cal J, 
Anna F1 and Capsicum), wilting symptoms were observed from week 2 and 
by week 5 all plants had wilted (Table 4). Expression of sy mptoms on the 
Anna F1 and Cal J confirmed virulence of the bacterial isolate; Capsicum was 
thus dropped from further evaluation as a rootstock. 
 
62 
 
 
Table 4: Mean number of surviving plants following inoculation with R. 
solanacearum 
Treatment 7 days 14 days 
21 
days 
35  days 
Cal J 10a 2.7a 5.0a 0.0a 
Capsicum 10a 2.3a 4.3a 0.0a 
Anna F1 10a 2.0a 4.3a 0.0a 
Eggplant 10a 10.0b 10.0b 10.0b 
Mt56 10a 10.0b 10.0b 10.0b 
Sodom 
apple 10a 10.0b 10.0b 10.0b 
 
NB: Values within day column followed by same letter are not significantly 
different at p<0.05 
 
 
 
 
 
 
                                                                   
Plate 5: Infected Capsicum (a) and Cal J (b) after inoculation compared to 
uninfected Solanum incarnum (c) and Solanum melongena (d) four weeks 
after Inoculation 
a b 
c d 
63 
 
 
4.3 Compatibility of bacterial wilt resistant rootstocks to scions of 
preferred tomato cultivars 
4.3.1: Grafting of the susceptible scion onto resistant rootstock 
Scions of the susceptible cultivars Anna F1 and Cal J were successfully 
grafted onto the wilt resistant rootstocks at different times with the take rate of 
the plants grafted at the young growth stage with that of old growth stage 
varying. Three days after grafting, only scions of Anna F1 and Cal J grafted on 
Sodom apple (rootstock) had established, but more than two thirds of the 
plants had taken in all the treatments fourteen days after grafting. 
Grafts combining Sodom apple (rootstock) + Cal J (scion) had the highest take 
(100%) followed by Eggplant + Anna F1 (96.7%), Mt56 + Anna F 1 (93.3%) 
while the least take was Mt56 + Cal J (76.7%) and Sodom apple + Anna F1 
(73.3%) (Figure 12). 
 
Figure 12: Proportion (%) of grafted plants fully healed /established 
fourteen days after grafting 
64 
 
 
4.3.2 Compatibility of the resistant rootstock and susceptible scions 
4.3.3 Sodom apple as rootstock  
Both Cal J and Anna F1scions grafted on Sodom apple established in the third 
day of grafting. However, the stem of sodom apple did not expand 
proportionately to that of Anna F1 and Cal J making it difficult for the 
rootstock to support the scions since there was overhang of scion tissue. At 
two weeks after grafting the seedlings bent due to weakness of the stem at the 
graft union. Therefore, though the rootstock and scion were compatible it 
could not be recommended (Plate 6). The grafted plants of sodom apple + 
Anna F1 established differently from the grafted plants of Sodom apple + Cal 
J. By the fourteenth day, all grafted Sodom apple + Cal J had established 
compared to Sodom apple + Anna F1 (Plate 6).  
 
 
 
 
 
  
 
Plate 6: Sodom apple + Cal J with bent roostock (extreme right) and the 
other plant with thin rootstock than the scion (left side) 
65 
 
 
4.3.4 Mt56 as rootstock 
Both Cal J and Anna F1 grafted on Mt56  were successful with two thirds of 
the plants established by the seventh day in all the treatments. Unlike the 
observation with Sodom apple, the Mt56 rootstock expanded in the same 
proportion to Cal J and Anna F1 scions (Plate 7) thus showing potential for 
growth. 
 
Plate 7: Healthy grafted plants of  Mt56 + Cal J with the rootstock and 
scion having the same diameter 
4.3.5 Eggplant rootstock + Cal J scion grafts 
In this treatment the grafting was successiful with more than two thirds of the 
grafted plants having established vascular connection within seven days in all 
the treatments. By the fourteenth day after grafting 90% of the plants had the 
graft union fully healed (Plate 8). 
66 
 
 
 
Plate 8: Healthy grafted plants of Eggplant + Cal J  with same diameter 
of rootstock and scion fourteen days after grafting 
Grafted plants of Eggplant and scions (Cal J and Anna F1) expanded at the 
same rate gaining an equal diameter that could adequately support the scion. 
4.3.6 Inoculation of grafted seedlings 
The plants grafted on Mt56, sodom apple and eggplant did not show any 
symptoms of wilting by two weeks after inoculation and had good growth 
vigor while the ungrafted susceptible seedlings of Cal J had started showing 
wilting symptoms one week after inoculation. Half of the ungrafted Cal J 
plants had wilted  by the fourteenth day after inoculation, and the bacterial wilt 
symptoms were observable (Plate 9).  
 
  
 
Plate 9: Healthy grafted plants of Eggplant + Cal J (A); wilted plants of 
ungrafted susceptible Cal J (B) two weeks after inoculation 
A B 
67 
 
 
4.3.7 Plant performance after transplanting the uninoculated grafted 
plants 
4.3.8 Plant Height  
 By the end of the eighth week after transplanting, the grafted plants of Mt56 + 
Anna F1 were the tallest (110.5 + 20.98 cm). The other grafted plants did not 
show significant difference in height amongst themselves; Eggplant + Anna 
F1 attained (78.25 + 22.91 cm), Mt56 + Cal J (76.25 + 11.99 cm) and Sodom 
apple + Anna F1 (68.75 + 8.33cm) while Eggplant + Cal J (59.0 + 4.93cm) 
and Sodom apple + Cal J (56.50 ± 2.25cm) were shorter, which indicated  
reduced growth rate (Figure 13). 
Rootstocks + Scion (Anna F1)              Rootstocks +  Scion (Cal J) 
                       
Figure 13: Mean height of grafted tomato seedlings after transplanting 
68 
 
 
4.3.9 Number of leaves 
The grafted plants of Mt56 + Anna F1 and Mt56 + Cal J had increased number 
of leaves fom week 1 to 4, the number then reduced between weeks 4, 5, and 
6. An increase in the number of leaves was observed from week 6 to 8. 
Eggplant + Anna F1 and Sodom apple + Anna F1 showed an increase in the 
number of leaves from week 1 to 8 and had no significant difference (P>0.05) 
between them. Eggplant + Cal J and Sodom apple + Cal J had fewer leaves 
with no significant difference (P>0.05) compared to each other.  
4.3.10 Flowering 
All the grafted plants flowered from week 4 to 8 with Mt56 + Anna F1 
achieving the highest number of flowers (14.25 ± 2.175) followed by Sodom 
apple + Cal J (12.5 + 1.258) in week 7. The same week Eggplant + Anna F1 
had the least number of flowers (6.5 + 4.093). By the end of week 8, grafted 
plants of Mt56 + Cal J had highest number of flowers (16.5.0 + 8.737) 
followed by Mt56 + Anna F1 (16.0 + 0.816). Eggplant + Anna F1 (7.75 + 
4.835) and Sodom apple + Anna F1 (13.75 ±3.119) showed significant 
difference (p<0.05) in the number of flowers while Eggplant + Cal J (13 ± 
5.066) and Sodom apple + Cal J (14.5 ± 0.289) did not have significant 
difference in the number of flowers (P>0.05) (Figure 14) 
69 
 
 
 
Figure 14: Mean number of flowers of tomato seedlings after 
transplanting 
4.3.11 Fruit yield in grams  
Fruit development started in week 6 after transplanting. The tomato fruits were 
harvested twice a week for five harvestings and the yield (grams) recorded. 
Amongst the grafted plants, the highest yielding treatment was Sodom apple + 
Anna F1 (484 gms ± 29.91), followed by Mt56 + Cal J (435 + 33.44) then 
Sodom apple + Cal J (420 ± 21.15) and Mt56 + Anna F1 (410 + 27.3). The 
grafted plants that had least yield were Eggplant + Anna F1 (390 + 23.65) and 
Eggplant + Cal J (364 ± 29.91) (Figure 15). 
 
70 
 
 
 
Figure 15: Mean yield of fruits produced by grafted tomato seedlings.  
Error bars 95% Confindence interval 
4.3.12 Plant performance after inoculation with Bacterial wilt pathogen 
Plant height 
The height of both the inoculated and uninoculated plants was determined  
while the grafted plants were still in polybags. Inoculation was done four 
weeks  after confirming compatibility when the grafted plants wer still in 
polybags 
Plant height of grafted plants comparing inoculated and uninoculated -
Anna F1 
In the combination of rootstocks and scion (Anna F1), grafted plants of 
Eggplant + Anna F1 was the tallest (37.65 ± 3.85cm) followed by Sodom 
apple + Anna F1 (33.67 ± 3.333 cm) while Mt56 + Ann F1 (32.58 + 0.917cm) 
71 
 
 
was the shortest (Figure 16A). For the uninoculated rootstocks + scion,  
Eggplant + Anna F1 had the highest height of 39.6 + 0.04 cm but not 
significantly different to Sodom apple + Anna F1 (37.62 ± 1.375) (P>0.05) 
(Figure 16B) 
 
72 
 
 
 
Rootstocks + Anna F1 (Inoculated) – A Rootstock+Ann F1(uninoculated)-B 
               
Figure 16: Mean height of Anna F1 grafted plants inoculated (A), and 
uninoculated (B) 
 
 
 
 
 
 
 
 
 
 
 
 
 
73 
 
 
 
Plant height of grafted plants comparing inoculated and uninoculated- 
Cal J  
The inoculated combination of rootstocks + scion (Cal J), Mt56 + Cal J had 
the highest height (36 ± 1.0 cm) while Sodom apple + Cal J (29.9 ± 4.3 cm) 
and Eggplant + Cal J (29.0 ± 0.2 cm) had no significant difference in height 
(p>0.05) (Figure 17A). The uninoculated rootstocks, Mt56+ Cal J had a higher 
height (34.17 ± 2.5) than Eggplant + Cal J (32.7 ± 2.7 cm) while Sodom apple 
+ Cal J had reduced height of 29.2 ± 3.4 cm. (Figure 17B). 
 
 
 
 
 
 
 
 
 
 
Figure 17: Mean height of Cal J grafted plants inoculated (A), and 
uninoculated (B) 
4.3.13 Number of leaves 
The number of leaves for both the inoculated and uninoculated were recorded 
from week 1 to  8. There was an increase in the number of leaves from week 1 
Rootstocks + Cal J 
(inoculated) - A  
Rootstocks + Cal J 
(Uninoculated) -B  
74 
 
 
 
to 8 with no significant difference (p>0.05) between the inoculated and the 
uninoculated seedlings grafted with Anna F1 as scion (Figure 18). For Cal J 
(scion), seedlings grafted to Mt56 had significantly more leaves than those 
grafted on rootstocks of sodom apple and eggplant for both inoculated and 
uninoculated. (Figure 19). 
   
Figure 18: Mean number of leaves on seedlings of tomato cultivar Anna 
F1 grafted on Mt56, Sodom apple and Eggplant. The number of leaves 
was recorded weekly 
75 
 
 
 
            
 
Figure 19: Mean number of leaves on seedlings of tomato cultivar Cal J 
grafted on Mt56, Sodom apple and Eggplant. The number of leaves was 
recorded weekly 
4.3.14 Mean number of flowers 
The cumulative number of flowers  was recorded weekly from week 4 to 8 
after inoculation. An increase in the number of flowers was noted from week 4 
to 8 across the treatments (Figure 20). Uninoculated seedlings of Sodom apple 
+ Anna F1 and Mt56 +Cal J had the highest mean number of flowers 7.5 + 
0.25 and 7.0 ± 1.33 respectively (Figure 21). 
76 
 
 
 
  
Figure 20: Mean number of flowers produced by the inoculated and  
uninoculated  grafted tomato plants with Anna F1 scions 
 
    
Figure 21: Mean number of flowers produced by the inoculated and  
uninoculated  grafted tomato plants with Cal J scions 
77 
 
 
 
4.3.15 Fruit yield  
The fruits were harvested twice a week for five harvestings and the yield 
recorded in grams for the inoculated and uninoculated grafted plants. Among 
the inoculated grafted plants, Sodom apple + Cal J had more weight (61.0 + 
4.0 gms) followed by Sodom apple + Anna F1 (45.0 ± 6.88 gms), Mt56 + 
Anna F1 (40.0 +5.0) and Eggplant + Anna F1 (35.5 ± 0.50) while the least 
yielding was Eggplant + Cal J (21.0 + 6.0 gms) compared to the uninoculated 
grafted plants where Sodom apple + Anna F1 yielded more (70.6 + 1.88 gms) 
followed by Mt56 + Anna F1 (35.0+5.0), Eggplant + Cal J (34.5 + 6.0) and the 
least yielding was Sodom apple + Cal J (28.5 + 13.50gms) (Figure 22). 
 
Figure 22: Yield of fruits produced by inoculated and uninoculated 
tomato plants. Error bars 95% Confidence Interval 
4.4 Effect of stage of growth on success of grafting 
The young (2-3 leaf) stage had the highest number of grafted plants that had 
taken successfully which was comparable to the old stage (4-5 leaf). In the 
78 
 
 
 
young stage,  Mt56 + Anna F1 had the highest mean number of successfully 
grafted plants (93.3%) followed by Eggplant + Anna F1 (86.7%), Sodom 
apple +  Cal J (83.3%), Mt56 + Cal J (80%) while Eggplant + Cal J and 
Sodom apple + Anna F1 had the same percentage take (63.3%). In the old 
stage, Mt56 + Anna F1 had a higher grafts take (43.3%), Eggplant + Anna F1 
and Sodom apple + Cal J had 33.3% take, Mt56 + Cal J and Sodom apple + 
Anna F1 had least number of successfully grafted plants with 23.3% take and 
20.3% take respectively (Figure 23). 
 
Figure 23: Proportion (%) of successfully grafted plants at two growth 
stages 
 
79 
 
 
 
CHAPTER FIVE:  DISCUSSION 
5.1 Tomato production in Mwea East 
The higher number of tomato producers in Tebere is attributed to water 
availability for irrigation, use of  hybrid seeds, and better all weather roads 
which enable farmers and buyers to transport tomatoes to market. Due to close 
proximity to the Mwea rice irrigation scheme farmers in Tebere have better 
access to water supply and  better maintained all weather roads. Although 
farmers in Nyangati are connected to irrigation canals, water scarcity due to 
rationing often causes water stress or plant death. Murinduko area is at a 
higher altitude with less water available, and farmers mostly rely on rainfall. 
The male dominance (70%) in tomato production in the area could be due to 
the fact that the crop is capital intensive and men generally have better access 
to capital than women. Anang et al. (2013) reported a similar reason for male 
dominance in tomato production in Wenchi Municipal District in Ghana. 
The higher participation of middle aged farmers (18 – 36 years) who are in 
their energetic and productive years is an indication of economic potential of 
tomato in the area. A similar scenario of age distribution of tomato farming is 
reported by Asare-Bediako et al. (2007) at Bontanga Irrigation Project in 
Ghana. Although agroecological conditions of the area are well suited for 
other horticultural and food crops (Mwangi et al., 2015), the results confirm 
that farmers have identified tomato as the most promising crop. As reported by 
Waiganjo et al., (2006), tomato production in the three locations utilizes more 
80 
 
 
 
than one third of the total cultivated land, which further confirms the 
importance of the crop. 
The observation that most farmers did not have adequate knowledge of insect 
pests and diseases affecting tomato shows need to strengthen the extension 
service. As reported by Mbaka et al. (2013), farmers received extension 
information from Agro – input vendors, Ministry of Agriculture, electronic 
media (Radio + TV) and field agronomists from agrochemical companies. The 
study also indicated that farmers lacked adequate information on sound crop 
and disease management. Poor disease identification was also noted for most 
growers, which can lead to ineffective disease management practices being 
applied, leading to increased cost of production and yield loss. Mbaka et al. 
(2013) and Weirsinga et al. (2008) reported that farmers depend on inputs 
suppliers for information, reading from the labels and experience from the 
usage of the product. Some of the products that farmers have been advised to 
use for the control of diseases and pests could lead to environmental 
degradation and pollution (Huat, 2014) as well as higher MRLs in fresh 
produce if excessively used. 
5.2 Management of pests in tomato production 
Despite a long history of pesticides use in control of pests and diseases in the 
area, farmers lacked knowledge on pesticides application and target, thus 
common pests such as whiteflies, thrips, aphids and diseases such as bacterial 
wilt, tomato yellow leaf curl, damping off, early and late blight, blossom end 
rot and verticilium wilt remain significant challenges due to resistance to 
81 
 
 
 
pesticides and fungicides, poor application practices and evolution of new 
biotypes. 
Further, the use of pesticides has made the problem of pest worse due to 
extermination of natural enemies (Waiganjo et al., 2006). Field hygiene such 
as removal of the affected plants was not practiced thus increasing the chances 
of disease spread. 
Pesticides and fungicides are expensive, therefore farmers tend to buy cheaper 
chemicals and use them at lower rates than recommended, which leads to 
increased density. To assess pests and diseases problems, close monitoring of 
the crop (scouting) is done to ensure use of appropriate management measures. 
Farmers should also be trained on Integrated Pest Management (IPM) and safe 
handling of pesticides as recommended by Waiganjo et al., (2006).  
Access to tomato seeds and seedlings is a challenge because the hybrid seeds 
are expensive and some farmers cannot afford them. This makes farmers to 
prefer seed that may not be hybrid, and often less  tolerant to diseases. With 
high cost of hydrid seeds, number of farmers select fruits which they extract 
seeds for subsequent planting. Fruits from infected plant may produce infected 
seedlings leading to disease spread. Ralstonia solanacearum spread through 
seeds has been reported by Moffet et al. (1981) and Ramsubhag et al. (2012) 
who showed that Bacterial wilt can be transmitted to cotyledons and leaves of 
tomato and capsicum plants from contaminated seeds. 
 
 
 
82 
 
 
 
5.3 Technologies used in management of Bacterial wilt: Nursery 
production 
Soil embedded on shoes and farm equipments has contributed to increased rate 
of disease spread. To avoid risks associated with soil nurseries, some farmers 
have adopted use of germination trays where artificial media is used. Use of 
artificial media guarantees disease free seedlings as reported by Mbaka et al. 
(2013). With this method farmers can reduce seed wastage and also achieve 
excellent crop stand as seedlings from trays have high rate of survival 
(Weirsinga et al., 2008). Establishing nurseries on soil that is already infected 
by Ralstonia solanacearum was identified to contribute significantly to the 
spread of the disease. Infected seedlings from such nurseries contribute to 
infect clean fields spreading the disease. This was observed in the locations 
where the survey was conducted and has also been reported by Nyangeri et al. 
(1984) and Ajanga (1993). 
5.4 Cultural practices used for control of Bacterial wilt: Crop Rotation 
Reduction of bacterial wilt with crop rotation has also been reported by 
Autrique and Ports (1978) and Melton and Powell (1991). As reported by 
Martin and French (1985), crop with non – host plant relationship has been 
reported to reduce the Ralstonia solanacearum concentration in the soil. 
Irrespective of the previous crops, farmers in the three locations showed 
preference to tomato due to its higher income potential thus they do not 
oftenly practice rotation. The findings are also in line with reports by Jackson 
and Gonzalez (1981) and Wimer et al. (2009) who reported that long term 
crop rotation for small holder farmers is challenging due to land constraints. 
83 
 
 
 
Crop rotation is rendered ineffective due to diminishing land sizes and 
therefore, farmers could not afford the long term rotational cycles (3years) 
(Sally et al., 2006). Intercropping can reduce disease by 73% (Boudreau, 
2013) as there is direct pathogen inhibition due to non – host relationship. 
5.5 Use of resistant varieties 
Plant resitance remains one of the most effective options of bacterial wilt 
management but is limited by lack of resistant varieties that also meet market 
requirements. Use of tolerant varieties to the disease has been reported by 
(Tachawangstien, 2009)  and Wimer et al. (2009). In India no variety was 
resistant among 70 genotypes tested by Singh et al. (2014b). However, some 
of the varieties tested showed high tolerance. Varieties that are mostly grown 
by farmers such as Kilele F1 from Syngenta, Rambo from Kenya Highland 
Seeds and VL -642 from Seminis have high tolerant to Bacterial wilt but use 
of second generation seeds nullifies the resistance since the extracted seeds 
may be from infected fruits.  
5.6 Compatibility of bacterial wilt resistant rootstocks 
The candidate species that were used as scions included Anna F1 (con 
ventional variety) and Cal J (open pollinated variety) and the rootstocks were 
resistant tomato variety Mt56, Eggplant (Solanum melongena) and Sodom 
apple (Solanum incarnum). The species were found to be resistant  to bacterial 
wilt after screening. From the study, the results showed that grafted plants 
were resistant to Ralstonia solanacearum and did not exhibit any wilting 
symptoms. Excellent tolerance to soil borne bacterial wilt was exhibited  by 
84 
 
 
 
the vigorous roots of the rootstock though the degree of tolerance varied 
considerably with the rootstock. However, the disease resistance mechanism 
in grafted plants need to be intensively investigated.  
Sodom apple (Solanum incarnum) is a resistant/tolerant plant. However, the 
challenge with this species is that the seeds are not readily available in Agro – 
vet shops and Agrochemical industries but are extracted from the fruits. From 
research, it is found that when grafted with the tomato scion, sodom apple  
(rootstock) grows at a slower rate than the scion and has a narrower diameter 
than the scion, thus can not fully support the growing plant. Eggplant is 
readily available in Agro – vet shops at prices that are affordable to farmers.  
Eggplant has deep  roots with  several root hairs for proper feeding. Mt56 is 
not being grown for direct sale because it does not meet the market demand in 
terms of quality and size. The Mt56 seeds are also not readily available for 
farmers in Kenya. Research has confirmed the resistance of the variety before 
and after grafting with  bacterial wilt susceptible variety Onyx (Waiganjo et 
al., 2011). 
There are various challenges that are associated with grafting and cultivating 
grafted seedlings. There was physiological challenge of producing 
adventitious roots from the scion by some grafted plants, the formation of the 
adventitious roots may be caused by poor alignment of vascular cambium of 
both the rootstock and the scion and unequal diameter of the rootstock and 
scion (Davis, 2010). The roots if allowed to grow into the soil, present the risk 
85 
 
 
 
of reinfecting the plant through by- passing the resistant rootstock leading to 
the death of the entire plant. 
Other challenges include skilled labor and techniques required for grafting 
operation and postgraft handling of grafted seedlings for rapid healing for 
approximately seven days (Jung, 1994). 
That the grafted Cal J and Anna F1 plants onto tolerant Eggplant, Sodom 
apple and Mt56 did not show any wilting symptoms implies the rootstocks 
were resistant to bacterial wilt and can be used in breeding programs to 
improve the preffered tomato varieties. High tolerance to bacterial wilt by wild 
variety (Sodom apple) is possible because the variety has tolerance gene that 
have been passed on from generation to generation. High bacterial wilt 
tolerance was reported by Lu et al. (2003) when wild Chinese tomato cultivars 
were used the varieties were reported to have reduced disease incidence by 
100% as well as delayed symptoms when compared to non grafted susceptible 
varieties. There was no flower formation and fruit development in ungrafted 
Cal J because the seedlings died before reaching maturity. 
During transplanting, it was ensured that the graft union remained above the 
soil line. From research it was found that if the graft union is buried, scion will 
root into the soil and any advantages that would have been provided by the 
rootstock, such as resistance to soil – borne diseases will be nullified as 
reported by Black et al. (2003) that the graft union must be kept above the soil 
line. This because the closer the graft union is to the soil line, the more likely 
adventitious roots from the scion will develop and grow into the soil. If this 
occurs, diseases can bypass the resistant rootstocks and may lead to infection 
86 
 
 
 
and death of the entire plant. The small sized fruits of Mt56, Eggplant and 
Sodom apple (rootstock)  with  Cal J (scion) combination could be due to 
incomplete pollination of the grafted plants, extreme temperature and poor 
plant nutrition status ( Gu, 2012) and  morphological characteristic of Cal J 
which produces small sized fruits. There was less number of flowers in these 
combinations due to poor feeding resulting to flower abortion, small fruit size 
and hence low yield. There was shedding of dry leaves resulting to decreased 
number.  
All the grafted plants both in the greenhouse and open field were found to be 
resistant/tolerant to bacterial wilt disease through out the entire research and 
exhibited good growth vigor. 
5.7 Effect of grafting practice and growth stage on success of grafting 
Cleft grafting was found to be the best practice for grafting compared to the 
tube grafting. Cleft grafting took short duration to graft and required less skill 
to combine the rootstock and scion. Two growth stages were compared; the 
young  (2 – 3 leaf) stage and old (4 -5 leaf) stage.  
In the young stage, grafting was easy and fast because the cambium layer is 
young and has not hardened, therefore cutting the rootstock and the scion into 
the required angle and aligning their diameter during grafting is not difficult. 
In this stage, the healing process of the graft union is fast and takes shorter 
time. The number of the grafted plants that heal and take in this stage is higher 
and the plants grow and develop faster compared to the old stage. 
Grafting in the old stage was hard and slow because the cambium layer has 
become woody, therefore cutting the rootstock and the scion into the required 
87 
 
 
 
angle and aligning their diameter during grafting is difficult. When the 
diameter is not properly aligned the grafted plant heals slowly, has poor 
nutrient uptake and eventually the plant dies. The number of the grafted plants 
that heal and take in this stage is lower and they exhibit poor growth.  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
88 
 
 
 
CHAPTER SIX:  CONCLUSION AND RECOMMENDATIONS 
6.1 Conclusions 
Bacterial wilt of tomato was found to be present in Mwea East locations of 
Kirinyaga County and is a great challenge affecting tomato production. The 
study showed that poor farming practices have contributed to quick spread of 
the disease within the field as well as in the neighbouring fields and new areas 
too. The study also indicated that farmers have limited information on the 
disease and are using less effective management strategies. There exist 
rootstocks of solanaceae family (Eggplant, Sodom apple and tomato Mt56) 
that are tolerant to bacterial wilt. The rootstocks and scions were compatible 
on Mt56 + Anna F1 (93.30% take), S. melongena + Anna F1 (96.7% take), S. 
incarnum + Anna F1 (73.3% take), Mt56 + Cal J (76.7% take), S. melongena 
+ Cal J (83.3% take) and S. incarnum + Cal J (100% take). Eggplant (Solanum 
melongena) and  tomato Mt56 performed best with scions of Anna F1 and Cal 
J. The best grafting growth stage is the young stage (2 – 3 leaf) when the 
vascular cambium has not hardened. Grafting of susceptible tomato varieties 
such as Anna F1 and Cal J onto resistant rootstocks (Eggplant, Sodom apple 
and Mt56) was found to be effective in management of Ralstonia 
solanacearum.  
6.2 Recommendations 
1. Further studies on other solanaceous varieties such as tobacco and wild 
tomato  with potential for use in tomato grafting should be conducted 
2. There is need for cost benefit analysis of the tomato grafting 
technology 
89 
 
 
 
3. More research and experimental work to test resistant varieties which 
do not require grafting 
4. Capacity building of nursery operators to use resistant rootstock  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
90 
 
 
 
REFERENCES 
Abdullah, H. (1998). Biology and survival of Pseudomonas solanacearum in 
Malaysia Ph.D Thesis, University of Pertanian, Malaysia. 
Abedayo, O. S, Kintomo, A. A and Fadamiro, H. Y. (2009). Control of 
bacterial wilt disease of tomatoes through Integrated Crop Management 
Strategies. International Journal of Vegetable Science, 15: 96-105. 
ISSN: 1936 – 5260, online 13931-5279. 
Acquaah, G. (2002). Horticulture: Principles and practices. New Jersey: 
Prentice Hall. 
Aganon, C. P., Mateo, L. G., Cacho, D., Bala, A. and Aganon, T. M. (2004). 
Enhancing off – season tomato production through grafted tomato 
technology. Philippine Journal of Crop Science, 27(2): 3-9.  
Agele, S. and Cohen, S. (2009). Effect of genotype and graft type on the 
hydraulic characteristics and water relations of grafted melon. J. Plant 
Interact. 4: 59-66. 
Agrios, G. N (1988). Plant Pathology. 3rd Edition. AcademicPress. ISBN 0 – 
12 – 044563-8. 
Ajanga, S. (1993). Status of bacterial wilt disease in Kenya. In Bacterial Wilt: 
Proceedings of an International Conference held in Kaohsiung, Taiwan, 
28 – 30 October 1992  G.L. Hartman and A.C. Hayward eds. Australian 
Centre for International Agricultural Research (ACIAR), Canberra, 
Australia. 45: 338-340. 
Akira, M., Kazuhiro, N.,Masao, S., Hideki, T. and Shigehito, T. (2009). 
Visualization of Ralstonia solanacearum cells during biocontrol of 
Bacterial wilt disease in tomato with Phythium oligandrum. General 
plant pathology, 75: 281-287. 
Allen, C., Prior, P. and Hayward, A. C (editors) (2005). Bacterial Wilt Disease 
and the Ralstonia solanacearum Species Complex. Pgs. 29 – 33. APS 
Press, St. Paul, Minnesota U.S.A. 
Allen, C., Jeffrey B., Jones and Carrie H. (2009). Bacterial Wilt of Tomato, 
USDA-NRI Project: R. solanacearum race 3 biovars 2: detection, 
exclusion and analysis of a Select Agent, Educational modules. 
Allen, C., Jones, J. B., Harmon, C. and Momol, T. M (editors) (2008). 
Ralstonia solanacearum /Culture Medium. USDA-NRI Project - R. 
91 
 
 
 
solanacearum Race 3 biovar 2: Detection, exclusion and analysis of a 
Select Agent pathogen .University of Wisconsin; University of Florida. 
Aloni, R. (1980). Role of auxin and sucrose in the differentiation of sieve and 
tracheary elements in plant tissue cultures. Planta 150: 255-263. 
Aloni, R. (1987). Differentiation of vascular tissues. Ann. Rev. Plant Physiol. 
38: 179-204. 
Aloni, R. (1995). The induction of vascular tissues by auxin and cytokinin. In: 
Davies, P. J. (Ed.), Plant Hormones. Kluwer Academic Publishers, 
Netherlands, pp. 531-546.  
Aloni, R. (2001). Foliar and axial aspects of vascular differentiation 
hypotheses and evidence. J. Plant Growth. Regul. 20: 22-34. 
Aloni, B., Karni, L., Deventureo, G., Levin,  Z., Cohen, R. and Katzir, N. 
(2008). Physiological and biochemical changes at the rootstock - scion 
interface in graft combinations between Cucurbita rootstocks and a 
melon scion. J. Hortic. Sci. Biotechnol. 83: 777-783. 
Anang, B. T., Zulkarnian, A. Z. and Yusuf, S. (2013). Production constraints 
and measures to enhance the competitiveness of tomato industry in 
Wenchi Municipal District in Ghana. American Journal of Experimental 
Agriculture, 3 (4): 824-838. 
Asare – Bediako, E., Showemino, F. A., Buah, J. N. and Ushawu, Y. (2007). 
Tomato production constraints at Bontaga Irrigation project in Northern 
Region of Ghana. Journal of Applied Sciences, 7: 459-461. 
Asian Vegetable Research and Development Center. (AVRDC) (2003). 
Progress report.Variations of Anti – oxidants and their activity in 
tomatoes. pg 70-115. 
Asian Vegetable Research and Development Center (2008). AVRDC Report 
2005: Bacteriology; Phylotype identification and Phylogenic 
relationships of Ralstonia solanacearum strains isolated in a different 
hosts in Taiwan. AVRDC publication Number 08 – 702. Shanhua, 
Taiwan: AVRDC -The World Vegetable Center. p4. 
Atkinson, C. J., Else, M. A., Taylor, L. and Dover, C. J. J. (2003). Root and 
stem hydraulic conductivity as determinants of growth potential in 
grafted trees of apple (Maluspumila Mill.). Exp. Bot. 54 (385): 1221. 
 
92 
 
 
 
Ateka, E. M., Mwang’ombe , A. W. and Kimenju, J. W. (2001). Reaction of 
Potato cultivars to R. solanacearum in Kenya. African Crop Science 
Journal, 9: 251-256. 
Autrique, A. and Potts, M. J. (1987). The influence of mixed cropping on the 
control of potato Bacterial wilt (Pseudomonas solanacearum). Annals 
Applied Biology, 111: 125-133. 
Bareja, B. G. (2011). What is grafting? Uses in Addition to Plant Propagation. 
Crop Agriculture Review.-\. Retrieved on 19th May, 2014. 
Black, L. L., Wu, D .L., Wang, J. F., Kalb, T., Abbass, D. and Chen J. H. 
(2003). Grafting tomatoes for production in hot – wet season. 
International Cooperators Guide. AVRDC pub: 03-551. 
Brewer, M. T., Moyseenko, J. B., Moonforte, A. J. and Esther, Van der. K. 
(2006). Morphological variation in tomato: A comprehensive study of 
quantitative trait loci controlling fruit shape and development. Journal of 
Experimental Botany, 58(6): 1339-1349 
Boudreau, M. A. (2013). Diseases in intercropping systems. Annual Review of 
Phytopathology, 51: 499-519. 
Burt, J. (2005). Growing Capsicum and Chillies. Deparment of Primary 
Industries – Vegatable resource Database. Pub. DAWA, Farmnote; 
64/99. 
CABI (2005a). Sub-title; Damage caused by Bacterial wilt of tomato/eggplant. 
www.infonet-biovision.org/default/ct/79/pests, Retrieved, 2nd March, 
2013. 
CABI (2005b). Tomatoes. In Hauvelink E. (Ed. Wageningen University, the 
Netherlands – Crop producion Science in Horticulture Series No. 13. 
Champoiseau, P. G. and Momol, T. M. (2009). Training modules on bacterial 
wilt of tomato. University of Florida IFAS extension. 
http://plantpath.ifas.ufl.edu/rsol/Trainingmodules/BWTomato_module.html  
Chen WY. (1984). Influence of the root – knot nematode on wilt resistance of 
flu-cured tobacco infested by Pseudomonas solanacearum. Bulletin of 
the Tobacco Research Institute, 21:41-48. 
 
93 
 
 
 
Chellemi, D. O., Dankers, H. A., Olson, S. M., Hodge, N. C. and Scott, J. W. 
(1997). Evaluating bacterial wilt – resistant tomato genotypes using 
regional approach. American Journal of Horticultural Science, 119: 326- 
329 
Coyne, D. L., Nicol, J. M and Claudius-Cole, B. (2007). Practical plant 
Nematology: a field laboratory guide. SP-IPM Secretariat, International 
Institute of Tropical Agriculture (IITA), Cotonu, Benin. 
Coaker, G. L., Meula, T., Eileen, A. K., Jones, A. K. and Francis, D. M. 
(2002). A QTL controlling stem morphology and vascular development 
in Lycopersicon esculentum x Lycopersicon hirsitum (Solanaceae) 
crosses is located on chromosome 2. American Journal of Botany, 89 
(12):1859-1866. 
Cohen, R., Burger, Y., Koern, A., Edelstein, M. (2007). Introducing grafted 
cucurbits to modern agriculture; The Israeli experience. Plant Dis. 91: 
916-923. 
Cuppels, D. A., Hanson, R. S. and Kelman, A. (1978). Isolation and 
characterization of bacteriocin produced by Pseudomonas 
solanacearum. Society of General Microbiology, 109: 295-303. 
Davis, A. R. (2010). Techniques of grafting. aggie 
horticulture.tamu.edu/faculty/davis/…/M12_DAVI4493_00_SE_C12.pd
f. Retrieved 9th July, 2016  
Deberdt, P., Queneherve, P., Darrasse, A. and Prior, P. (1999). Increased 
susceptibility to bacterial wilt in tomatoes by nematode galling and the 
role of the Mi gene in resistance to nematodes and bacterial wilt. Plant 
Pathology Journal, 48: 408-414.  
Deberdt, P., Oliver, J., Queneherve, P. and Prior, P. (1999). Evaluation of 
bacterial wilt resistance in tomato lines nearly isogenic for Mi gene for 
resistance to root - knot. Plant Pathology Journal, 48: 415-424. 
Dengler, N.G. (2001). Regulation of Vascular Development. J. Plant Growth 
Regul. 20: 1-13. 
Dristig, M. C. G and Dianese, J. C. (1990). Characterization of Pseudomonas 
solanacearum biovars based on membrane protein patterns. 
Phytopathology, 80: 641-646. 
 
94 
 
 
 
Erbaugh, M., Kyamanywa, S., Karungi, J., Waiganjo, M. M. and Maerera, A. 
(2011). Ohio State University- Principal Investigator on Mt56, East 
Africa Regional Project; Uganda / Tanzania / Kenya. East Africa 
Program Summary. https://ipmil.cired.vt,edu/wp…/05/ipmcrsp-a11-12-
east-africa.pdf. 
Evanelia, M., Gizzi, S., Ross, R. and Rufini, S. (2005). Passion flower fruit – 
A new source of lycopene? Journal of Medicinal Food, 8(1): 104-106. 
Factfish website (2016). Kenya: Tomatoes, production quantity (tons). Source, 
FAOSTAThttp://www.factfish.com/statistic 
country/kenya/tomatoes,+production+quantity. Retrieved 10th Feb, 
2018. 
Faisal, H., Shaukat, S. S., Abid, M. and Akbar, M. (2013). Control of some 
important soil – borne fungi  by chitin associated with Chilli 
(Capsicum annum L) in the Sindh, Pakistan. Article of Science  
Technology and Development, 32(3): 228-234. 
Fajinmi A. A. and Fajinmi O.B. (2010). An overview of Bacterial wilt disease  
of tomato in Nigeria. Agricultural journal, 5(4): 242-247 
Fall, P. A., Fredrikson, M., Axelson, O. and Granenus, K. K. (1999). 
Nutritional and occupational factors influencing the risk of Parkinson’s 
disease. A case control study in South eastern Sweden. Movement 
disorders, 14(1): 28-37. 
FAO (Food and Agricultural Organization). (2012). Statistical Database. 
Retrieved from http://www.faostat.org. 
Fernandez-Garcia, N., Carvajal, M. and Olmos, E. (2004). Graft union 
formation in tomato plants: Peroxidase and catalase involvement. Annals 
of Botany, 93: 53-60. 
Fernandez-Garcia, N., Martinez, V., Cerda, A. and Carvajal, M. (2002). Water 
and nutrient uptake of grafted tomato plants grown under saline 
conditions. Journal of Plant Physiology, 159 (8): 899-905. 
Flaishman, M. A., Loginovski, K., Golobowich S. and Lev-Yadun, S. (2008).  
Arabidopsis thaliana as a model system for graft union development in 
homografts and heterografts. J. Plant Growth Regul. 27: 231-239 
10.1007/s00344-008-9050. 
95 
 
 
 
Genova C., Schreinemachers P., Afari – Sefa V. (2013). An impact assessment 
of AVDRC – the World Vegetable Center, Shanhua, Taiwan. AVDRC 
Publication No. 13 – 773.52p (Research Action; no.8). 
Geoffrey, S. K., Hillary, N. K., Antony, K. M., Maram, M. and Mary, M. C. 
(2014). Challenges and strategies to improve tomato competitiveness 
along the tomato value chain in Kenya. International Journal of 
Business Management, Vol. 9. 9, No.9: 2014. ISSN 1833 – 3850 E- 
ISSN 1833 – 8119. Published by Canadian Center of Science and 
Education. 
GoK (Government of Kenya). (2012). National Horticulture Policy. Ministry 
of Agriculture, Kilimo House, Nairobi. 
Gomes, A. M., Mariano, R. L., Micherett, and De Franca, S. J. (1994). 
Selection of processing tomato progenies for resistance to Ralstonia 
solanacearum. In: Bacterial wilt disease, molecular and ecological 
aspects. Prior, P., Allen, C. and Elphiastone, J. (Eds), pp. 267 – 283. 
Reports of the second international bacterial wilt symposium held in 
Gosier, Guadaloupe, France. 22-27. 
Guan, W., Zhao, X., Hassel, R. and Thies, J. (2012). Defense mechanisms 
involved in disease resistance of grafted vegetables. 
HortScience, 47:164–170 
Guo, J. K., Oj, H. O., Guo, Y. H., Ge, H. L., Gong, L. Y., Zhang, L. X. and 
Sun, P. H. (2004). Biocontrol of tomato wilt by plant growth – 
promoting rhizobacteria. Microbiology Review, 29: 66-72. 
Gupta, S. K. and Thind, T. S. (2006). Disease Problems in Vegetable 
Production. Pawan Kumar, Scientific Publishers, India. ISBN: 81-7233-
452-3 (H.B); 81-7233-453-2 (P.B), Sub – Title; Diseases of Tomatoes. 
Pg 65-104. 
Gu, S. (2012). Innovative Small Farmers’ Outreach Program (ISFOP): West 
Central Region. Vegetable grafting. Volume 2 issue 4. 
Grimault, V. and Prior, P. (1994). Grafting tomato cultivars resistant or 
susceptible to bacterial wilt - analysis of resistance mechanisms. Journal 
of Phytopathology, 141:330-334. 
Grimault, V., Gelie, B., Lemattre, M., Prior, P. and Schmit, J. (1994). 
Comparative histology of resistant and susceptible tomato cultivars 
infected by Pseudomonas solanacearum. Physiological and Molecular 
Plant Pathology, 44:105-123. 
96 
 
 
 
Grimault, V., Anais, G. and Prior, P. (1994). Distribution of Pseudomonas 
solanacearum in the stem tissues of tomato plant with different levels of 
resistance to bacterial wilt. Plant pathology, 43: 663-668. 
Grigoriadis, I., Nianiou-Obeidat, I. and Tsaftaris, A. S. (2005). Shoot 
regeneration and micrografting of micropropagated hybrid tomatoes. 
Journal of Horticultural Science and Biotechnology, 80: 183-186. 
Haas, D. and De Fago, G. (2005). Biocontrol of soil-borne pathogens by 
fluorescent pseudomonas. Review of microbiology, 3(4): 307-319. 
Hanson, P. M., Wang, J. F., Licardo, O., Hanudin, Mah, S. Y., Hartman, G. L., 
Lin, Y. C. and Chen, J.T. (1996). Variable reactions of tomato lines to 
bacterial wilt evaluated at several locations in south East Asia. 
Hortscience, 31: 143-146. 
Hartman, G. L. and Elphinstone, J.G. (1994). Advances in control of 
Pseudomonas solanacearum race 1 in major food crops. In: Hayward A. 
C and G. L. (Eds.). Bacterial wilt: The disease, its causal agent, P. 
solanacearum. 32; 157-177. 
Hayward, A. C. (1964). Characteristics of Pseudomonas solanacearum. 
Journal of Applied Bacteriology, 27: 265-277. 
Hayward, A. C. (1991). Biology and epidemiology of bacterial wilt caused by 
Pseudomonas solanacearum. Annual Phytopathology, 29: 65-87. 
Horticultural Crops Development Authority (HCDA) (2010). Marketing News 
Vol.6, Issue No.2., Nairobi, Kenya. 
Horticultural Crops Development Authority (HCDA) (Aug, 2011). 
Horticulture performance 2010 - 
2012.pdf.www.hcda.or.ke/statistcs/2012/Horticulture%20performance%
20201020to%2012. Retrieved 20th March, 2014. 
Horticultural Crops Development Authority (HCDA) (2012). Validated data 
on Horticulture performance 2012. Ministry of Agriculture – Kenya. 
Horticultural Crops Development Authority (HCDA) (2014). Horticulture 
validated report 2014.  
Humphrey, J. (2009). The supermarket revolution in developing countries: 
tidal wave or tough competitive struggle. Journal of Economic 
Geography, 7(4): 433 – 450. http://dx.doi.org/10.1093/jeg/ibm008. 
97 
 
 
 
Islam, T. M. and Toyota, K. (2004). Suppression of bacterial wilt of Tomato 
(Ralstonia solanacearum) by incorporation of composts in soil and 
possible mechanism. Microbes Environment,19: 53-60. 
Jackson, M. T. and Gonzalez, L. C. (1981). Persistence of Pseudomonas 
solanacearum (race 1) in a naturally infested soil in Costa Rica. 
Phytopathology, 71: 690-693. 
Jaw-Fen Wang and Chih-Hung Lin (2005). Integrated Management of Tomato 
Bacterial wilt. AVRDC, The World Vegetable centre. www.avrdc.org 
Ji, P., Momol, M. T., Olson, S. M., Pradhanang, P. M. and Jones, J. B. (2005). 
Evaluation of thymol as biofumigant for control of bacterial wilt of 
tomato under field conditions. Journal of Plant diseases and protection,  
124(89): 497-500. 
Jung, M. L. (1994). Cultivation of grafted vegetables I. Current status, 
Grafting Methods and Benefits. Department of Horticulture, Kyung Hee 
University, Suwon 449-701, Korea 
Johkan, M., Mitukuri, K., Yamasaki, S., Mori, G and Oda M. (2009). Causes 
of defoliation and low survival rate of grafted sweet pepper plants. Sci. 
Hortic. 119: 103-107 
Jones, J. B., Jones, P. J., Stall, R. E. and Zitter, T. A (editors, 1992). 
Compendium of Tomato Diseases. Pub. APS press: St. Paul, 
Minnesota.Vol.28, Issue No. 03. 
Jones, J. B. (2008). Tomato Plant Culture. In the field, greenhouse and garden. 
Taylor and Francis Group, USA 55. 
Karungi, J., Tusiime, G., Rubaihayo, P., Ssonko, R., Asiimwe, D., 
Kyamanywa, S., Miller, S. and Erbaugh, J.M. (2011). IPM of Ralstonia 
solanacearum on tomato in Uganda. EAST AFRICA Regional Project: 
Uganda / Tanzania / Kenya. 
Kavitha, R. and Umesha, S. (2007). Prevalence of bacterial spot in tomato 
field of Karnataka and effect of biological seed treatment on disease 
incidence. Crop protection Journal, 269 (7): 991-997.   
Kawaguchi, M., Taji A., Backhouse, D. and Oda, M. (2008). Anatomy and 
physiology of graft incompatibility in solanaceous plants. J. Hortic. Sci. 
Biotech. 83: 581-588. 
98 
 
 
 
Kelly, T. and Byerlee, D. (2004). Surviving on the margin: Agricultural 
research and development strategies for poverty reduction in marginal 
areas. Mimeo, Agriculture and Rural development, World Bank. 
Kelman, A. and Person, L. H. (1961). Strains of Pseudomonas solanacearum 
differing in pathogenicity to tobacco and peanut. Phytopathogenicity, 
51: 158-161. 
Kirimi Sindi. (2011). Tomato. Product description. 
https://www.msu.edu/~sindijul/Tomatoes%20in%20Kenya.htm.  
Lee, J. M. (1994). Cultivation of grafted vegetables: current status, grafting 
methods, and benefits. Hortscience, 29: 235-239. 
Liao, B. S.,  Shan, Z. H., Duan, N. X., Tan, Y. J., Lei, X., Li, D. and Mehan, 
V. K. (1998). Relationship between latent infection and groundnut 
bacterial wilt resistance. In: Bacterial wilt disease; Molecular and 
Ecological aspects. Prior, P., Allen, C., and Elphinstone, J. (Eds), 294 –
299. Reports of the second International bacterial wilt symposium held 
in Gosier, Guadaloupe, France, 22 – 27 June 1997. 
Lusweti A., Emily W., Paul S. and John M. (2011). Solanum incarnum 
(Sodom Apple). BioNET – INTERNATIONAL Secretariat – UK. 
Lu, M. A., Chen, Y. H., Lin, M. S. and Chien, H. P. (2003). An experiment 
using grafting for control of bacterial wilt. Plant protection Tokyo, 
18(3): 3-25 
Magambo, J.S., Kyamanywa, S., Ekwamu, A., Lerner, E. K., Luther, G. and 
Erbaugh, M. (2002). An alternative Approach to increasing tomato 
production by reducing incidences of Bacterial wilt through grafting. 
Research paper; Makerere University Agricultural Research, Kabanyolo. 
Presented at IPM CRSP year 10 at work plan meeting. 
Mahmoud, M. N., Boughalleb, N., Ouhaibi, N., Tarchoun, N., Souli, M. and 
Belbahri, L. (2010). Evaluation of grafting techniques and a new 
rootstock for resistance of pepper (Capsicum annum L.) towards 
Phytopthora nicotianae. Journal – Food, Agriculture and Environment 
(JFAE), Vol 8,  issue No. 1, pgs., 135 – 139; online ISSN: 1459 – 0262. 
Mallikarjun, Y. Kenganal and Byadgi (Dec, 2008). Farmers Note book on 
management of Bacterial wilt in tomato. 
www.Hindu.com/seta/2008/12104/stories/2008120450151500.htm. 
Retrieved 2nd Jan, 2013. 
99 
 
 
 
Maribel, M. and Paul, W.B. (2010). Grafting Capsicum to Tomato rootstock; 
Journal of Young Investigators, Vol. 20, Issue No.2 
Martínez-Rodríguez, M.M., Esta˜ n, M.T., Moyano, E., García-Abellán, J.O., 
Flores, F.B., Campos, J.F., Al-Azzawi, M.J., Flowers, T.J., Bolarín, 
M.C. (2008). The effectiveness of grafting to improve salt tolerance in 
tomato when an ‘excluder’ genotype is used as scion. Environ. Exp. Bot. 
63: 39-401.  
Mattsson, J., Ckurshumova, W., Berleth, T. (2003). Auxin signaling in 
Arabidopsis leaf vascular development. Plant Physiol. 131: 132-1339. 
Mbaka, J.N., Gitonga, J.K., Gathambiri, C.W., Mwangi. B.G., Githuka, P. and 
Mwangi, M. (2013). Identification of Knowledge and Technology gaps 
in high tunnel (‘greenhouse’) tomato production in Kirinyaga and Embu 
Counties .Presented during the 2nd National Science, Technology and 
Innovation week, 13th - 17th May, 2013, K.I.C.C., Nairobi. 
McAvoy, R. (Nov , 2005). Grafting Techniques For Greenhouse Tomatoes, 
Nov 10, 2005. 
Melton, T. A. and Powell, N. T. (1991). Effect of two – year crop rotations 
and cultivar resistance on Bacterial wilt in flue cured tobcco. Plant 
disease, 75: 695-698. 
Messiha, N. A. S (2006). Bacterial Wilt of Potato (Ralstonia solanacearum, 
races 3, biovars 2): Disease management, disease survival and possible 
eradication. PhD Thesis Wageningen University. Pp3-5. 
Moffet, M .L., Wood, B. A. and Hayward, A. C. (1981). Seed and soil source 
of inoculums for the colonization of foliage of solanaceous host by 
Pseudomonas solanacearum. Annals of Applied Biology, 98: 403-411. 
Momol, J. P., Olson, M. T., Pradhanang, P. M and Jones, J. B (2005). 
Evaluation of Thymol as biofumigant for control of Bacterial Wilt of 
Tomato under field conditions. Plant disease, 89: 497 – 500. 
Monsanto website. (2013). Tomato Anna F1 Handbook. 
http://www.monsantoafrica.com/pdfs/tomato_anna f1 
growers_handbook. pdf. Retrievd 27th April, 2015 
Moore, R., (1984a).  A model for graft compatibility–incompatibility in higher 
plants. Am. J. Bot. 71: 752-758. 
100 
 
 
 
Moore, R., (1984b). The role of direct cellular contact in the formation of 
compatible autografts in Sedum telephoides. Ann. Bot. 54: 127-33. 
Muchangi, J. (2012). The most popular fruits and vegetables unveiled. The 
Star.www.the.star.co.ke/news/article-20449/most-popular-fruits-and-
vegeatbles-unveiled. Retrieved 20th March, 2014. 
Mudge, K., Janick, J., Scofield, S. and Goldschmidt, E. E. (2009). A history of 
grafting. Hortic.Review. 35: 437–493 10.1002/9780470593776. 
Mwangi, W. M., Kimenju, J. W., Narla, R. D., Kariuki, G. M. and Muiru, W. 
M. (2015). Tomato management practices and diseases occurrence in 
Mwea West sub county. ISSN 2224 -3186 (Paper) ISSN 2225 – 0921 
(online). Journal of Natural Sciences Research,Vol.5, No. 20 (2015).  
Nakaho, K., Inoue, H., Takayama, T. and Miyagawa, H. (2004). Distribution 
and multiplication of Ralstonia solanacearum in tomato plants with 
resistance derived from different origins. General Plant Pathology, 70: 
115-119. 
Naika, S., Joep, L. D. J; Marja.de G and Martin, H. (2005). Cultivation of 
tomato, production and processing. Www. Journey to forever. Org/ 
farm-library /Ad17.pdf. Retrieved 03rd Nov, 2012. 
Nassiuma D. K. (2000). Survey Sampling: Theory and Methods. Njoro, 
Kenya: Egerton University Press 
Nguyen, M. T. and Ranamukhaarachchi, S. L. (2010). Soil-borne antagonists 
for biological control of Bacterial wilt disease caused by Ralstonia 
solanacearum in tomato and pepper. Journal of Plant Pathology, 92 (2): 
395 -406. Vol.92, Issue No. 2. 
Nyangeri, J. B., Gathuru, E. M. and Mukunya, D. M. (1984). Effect of latent 
infection on the spread of bacterial wilt in Kenya. Tropical Pest 
Management, 30: 163-165. 
Oda, M., Maruyama, M. and Mori, G. (2005). Water transfer at graft union of 
tomato plants grafted onto Solanum rootstocks. J. Jpn. Soc. Hortic. Sci. 
74: 458–463. 
Oda, M. (1995). New grafting methods for fruit-bearing vegetables in Japan. 
Japan Agricultural Research Quarterly 29:187-194. 
Oda, M. (1999). Grafting of vegetable to improve greenhouse production. 
College of Agriculture: Osaka Prefecture University. 
101 
 
 
 
Okabe, N. and Goto, M. (1963). Bacteriophages of plant pathogens. Annual 
review of Phytopathology,1: 397-418. 
Olmstead, M., Lang, N. S., Ewers F. W. and Owens, S. A. (2006). Xylem 
vessel anatomy of sweet cherries grafted onto dwarfing and non - 
dwarfing rootstocks. J. Am. Soc. Hortic. Sci. 131: 577-585. 
Olson, H.O. (2005). Ralstonia solanacearum. Requirement for PP 728 
Soilborne Plant Pathogens. 
Onduso, J. N. (2014). Management of Bacterial wilt of tomato by use of 
resistant rootstock. Masters Thesis, University of Nairobi 
Palada, M. C and Wu, D. L (2005). Increasing off – season tomato production 
using grafting technology for Peri – Urban Agriculture in South East 
Asia. ISHS ActaHorticulturae 742; International Conference and 
Exhibition on Soilless Culture: ICESC 2005. 
Peregrine, W. (1982). Grafting – A simple technique for overcoming bacterial 
wilt in tomato. Tropical pest management, 28: 71-76. 
Peterson, R. A., Inch, A. J., Herrington, M. E and Saranah, J. (1983). A tomato 
resistant to bacterial wilt biovars 3. Australian Plant Pathology, 12: 8-
10. 
Poethig R.S. (2009). Small RNAs and developmental timing in plants 
Curr Opin Genet Dev. 2009 Aug; 19(4): 374-378. 
Poffley, M. (March, 2003). Grafting Tomatoes for Bacterial Wilt Control. 
www.nt.gov-au/d/content/file/p/vegetable/603-pdf, ISSN: 0157-8243. 
Retrieved 23rd March, 2014. 
Prior, P. and Beramis, M. (1990a). Introduction de la resistance au 
fletrissement bacterrien du Pseudomonas solanacearum. In: Persley, G. 
J., ed., Bacterial wilt disease in Asia and South Pacific. ACIAR 
proceedings, 13: 105-111. 
Prior, P., Allen, C. and Elphinstone, J. G (editors) (1998). Bacterial Wilt 
Disease Molecular and Ecological Aspects. Pub; Springer – Verlag 
Berlin Heidelberg, New York. 
Purseglove, K. O. (1979). Tropical Crop dicotyledons. Longman, London, Pg. 
199 -237. 
102 
 
 
 
Ramsubhag, A., Lawrence, D., Cassie, D., Fraser, R., Umaharan, R., Prior, P. 
and Wicker, E. (2012). Wide genetic diversity of Ralstonia 
solanacearum trains affecting tomato in Trinidad, West Indes. Plant 
Pathology, 61(5): 844-857. 
Rivard, C. L and Louws, F. J. (2008). Grafting to manage soil borne disease. 
Hortscience. 43: 2104-2111. 
Rao, A. V. and Balachandran, B. (2002). Role of Oxidative stress and oxidants 
in neurodegenerative diseases. Nutritional Science, 5(5): 291-309. 
Rick, C. M. (1995). Tomato (Lycopersicon esculentum),  P 452 -  457. In J. 
Smart and N. W Simmonds (Eds). Evolution of crop plants, 2nd Edition, 
Longman, London. 
Rivard, C. L., O’Connel, S., Peet, M. M., Welker, R. M.  and Louws, F. J. 
(2012). Grafting tomato to manage Bacterial Wilt caused by Ralstonia 
solanacearum in the Southern Eastern United States. Journal of Plant 
diseases and protection, 96(7): 973-978. 
Rivard, C. L., and Louws, F. J. (2006). Grafting for Disease Resistance in 
Heirloom Tomatoes. College of Agriculture and Life Sciences. North 
Carolina Cooperative Extension Service 
Rost, T. L (1996). Lycopersicon esculentum, Tomato; Tomato Anatomy; 
Leaves Anatomy, Flowers and fruits anatomy. Section of Plant Biology, 
Division of Biological Sciences, University of California, Davis. 
Robertson, A. E., Wechter, W.P., Denny, T. P., Fortnum, B. A. and Kluepfel, 
D. A. (2004). Relationship between avirulence gene (avrA) diversity in 
Ralstonia solanacearum and bacterial wilt incidence. Molecular Plant-
Microbe Interactions,17:1376-1384. 
Ruiz, J.M., Belakbir, A., López-Cantarero, I. and Romero, L. (1997). Leaf-
macronutrient content and yield in grafted melon plants: a model to 
evaluate the influence of rootstock genotype. Sci. Hortic. 71: 227-234. 
Sacha, J., Kreider, P. and Carol, M. (2011). Vegetable grafting (Eggplant and 
Tomatoes). Cvu.cahe.wsu.edu/CEP publications/FSO52E, pdf.pub; 
Washington State University. Retrieved 23rd March, 2014. 
Saddler, G. S. (2005). Management of Bacterial wilt disease. APS Press ST. 
Paul, MN. 121-132. 
103 
 
 
 
Sally, A. M., Randal, C. R., and Richard, M. R. (2006). Fusarium and 
Verticillium wilt of Tomato, Pepper and Eggplant. The Ohio State 
University Extension 
Sant-Cruz, A., Martinez-Rodriguez, M. M., Perez-Alfocea, F., Romero 
Aranda, R. and Bolarin, M. C. (2002). The rootstock effect on the 
tomato salinity response depends on the shoot genotype. Plant Sci. 162: 
825-831. 
Schaad, N. W., Takatsu, A. and Dianese, J. C. (1978). Serological 
identification of strains of Pseudomonas solanacearum in Brazil. In: 
Proceedings of Forth International Conference on Plant Pathogenic 
Bacteria, Angers, France, 295-300. 
Schaad, N. W., Jones, J. B and Chun, M (editors) (2001). Laboratory Guide 
for Identification of Plant Pathogenic Bacteria. Pgs.151 – 166. APS 
Press. St. Paul, Minnesota. 
Scott, J. W., Wang, J. F. and Hanson, P. M. (2005). Breeding tomatoes for 
resistance to bacterial wilt, a global view. International Symposium on 
Tomato Diseases, 25th November, 2005. Orlando, FL, USA 
Scott, J. W. (1996). Tomato improvement for bacterial disease resistance for 
the tropics: A contemprary basis and future prospects. 1st International 
Symposium on Tropical Tomato Diseases. November, 21-22, 1996, at 
Recife, Pemambuco, Brazil. 
Seminis, Kenya.(2007). Retrieved from: 
http://www.freshplaza.com/news.html 10th  August, 2016 
Sharma, A. K. and John, B. N. (2002). Physiology of nutrient uptake by 
arbuscular mycorrhizal fungi. In: Sharma, A.K., Johri, B .N. (Eds.), VA 
mycorrhizas: interaction in soil, Rhizophere and Plant. Science 
Publishers, NewJersey, USA. pp. 279-308.  
Sharma, M. P., Gaur, A., Tanu, U. and Sharma, O. P . (2004). Prospects of 
arbuscular mycorrhizal in sustainable management of roots and soil – 
borne diseases of vegetable crops. In: Murkerji, K. G. (Ed.). Disease 
management of fruits and vegetables. Vol.1. Fruit and vegetables 
diseases. Kluwer Academic Publishers, The Netherlands 501- 539. 
Shibuya, T., Nakashima, H., Shimizu-Maruo, K., and Kawara, T. (2007). 
Improvement of graft development in tomato and eggplant grafted 
cuttings by supplying warmed water to graft union during low-air-
temperature storage. J. Jpn. Soc. Hortic. Sci. 76: 217-223. 
104 
 
 
 
Shilpi, F. and Umali – Deininger, D. (2008). Market facilities and Agricultural 
Marketing: Evidence from Tamil Nadu, India. Journal of Agricultural 
Economics, 39 (93): 281-294. 
http://dx.doi.org/10.1111/j.1514.08162.2009.0038.x 
Shimomura, T. and Fujihara, K. (1977). Physiological study of graft union 
formation in Cactus. II. Role of auxin on vascular connection between 
stock and scion. Jpn. Soc. Hortic. Sci. 45: 397-406. 
Sigei, K. G., Ngeno, K. H., Kibe, M. A., Mwangi, M. M. and Mutai, C. M. 
(2014). Challenges and strategies to improve tomato competitiveness 
along tomato value chain in Kenya. International Journal of Business 
and Management, 9 (9): 230-245. 
Sikirou, R., Beed, F., Ezin, V., Gbèhounou, G., Miller, S. A. and Wydra, K. 
(2004). First report of bacterial wilt of tomato (Solanum lycopersicum L) 
caused by Ralstonia solanacearum in Benin. 
Sikora E. J. (2004). Plant diseases note. Bacterial wilt of tomatoes. Alabama 
Cooperative Extension System. ANR – 862. 
Singh, D., Yadar, D . K., Sinha, S. and Choudhary, G. (2014b). Effects of 
temperature, cultivars, injury  of root inoculum load of Ralstonia 
solanacearum to cause Bacterial wilt of tomato. Phytopathology and 
Plant protection, 47(13): 1574-1583. 
Smith, J. J., Offord, L. C., Holderness, M. and Saddler, G. S. (1995). Genetic 
diversity of Burkholderia solanacearum (synonym Pseudomonas 
solanacearum) race 3 in Kenya. Applied and Environmental 
Microbiology, Vol 61, no.n12, 1995 Dec, p4263(6) (ISSN: 0099-2240) 
Ssejjamba, F. K. (2008). Value Chain Analysis – Fresh Tomatoes in Uganda 
and Kenya. Maastricht School of Management. Assignment 3. 
Srinivasan, R. (2010). Safer tomato production Techniques; A field guide for 
Soil Fertility and Pest management AVRDC – The World Vegetable 
Center, Shanhua Taiwan. AVRDC Publication No.10.Pg. 97. 
Stere, B. (2011). Plant diseases – Tomato wilt problems – pdf. Online- 
htts://uextension.tennessee.edu/publications/Documents/sp370-c.pdf. 
Retrieved 23rd March, 2014. 
 
105 
 
 
 
Suganuma, H., Hirano, T., Amiroto, Y. and Inakuna, T. (2002). Effects of 
tomato intake on striated monoamine level in a mouse model of 
experimental Parkinson’s disease. Journal of nutritional science and 
vitaminology, 48(3): 251-254. 
Tachawongstien, S., Thummabenjapone, P. and Bolkan, H. (2009). Screening 
tomato varieties for their Bacterial wilt resistance over seasons in 
Northern Thailand. Acta Horticulture 808: 263 – 268. 
http://www.actahort.org/books/808/808_40.htm. Accessed 15th October, 
2015. 
Tahat, M. M. and Kamaruzaman, S. (2010). Ralstonia solanacearum. The 
Bacterial wilt causal agent. Asian Plant Science, 9: 385-395. 
Tahat, M. M., Kamaruzaman, S. and Radiziah, O. (2011). Bio – compartments 
invitro system for Glomus mosseae and Ralstonia solanacearum 
interaction. International Botany, 7: 295 -299. 
Taylor, J. K., Westerbreek, P. J. and Dobrow, M .H. (2011). Acut above the 
rest: The utilization of resistant tomato rootstocks in managing Southern 
bacterial wilt in Eastern United States. URL 
http://ashs.org/abstracts/2011/abstract6952.html.Viewed on 24th January, 
2014. 
Tokuda, A., Shibuya, T., Kitaya, Y. and Kiyota, M. (2006). Bottom heat 
treatment reduces water stress of Cucurbitaceae and Solanaceae stock-
plant cuttings during low air temperature storage. J. Jpn. Soc. Hortic. 
Sci. 75: 285. 
Torii, T., Kawazaki, M., Okamoto, T., Kitani, O. (1992). Evaluation of graft-
take using a thermal camera. Acta Hortic. 319:  631-634. 
Turnbull, C.G (2010). Grafting as a research tool. Methods Mol Biol. 2010; 
655:11-26. 
Turquois, N., and M. Malone. (1996). Non-destructive assessment of 
developing hydraulic connections in the graft union of tomato. Journal 
of Experimental Botany 47:701-707. USDA (1999). Nutritional 
Database for standard reference, Release 13th November, 1999. 
Wambua, J. (2012). Popular Tomato Varieties. 
http://mfarm.co.ke/blog/post/Popular-Tomato-Varieties. Retrieved 20th 
Sept, 2014. 
106 
 
 
 
Waiganjo, M. M., Wabule, N. M., Nyongesa, D., Kibaki, J. M., Onyango, I., 
Wepukhulu, S. B and Muthoka, N. M. (2006). Tomato Production in 
Kirinyaga, District, Kenya, A Baseline Survey Report. KARI/IPM – 
CRSP Collaborative Project. 
Wamache, A. (2005). Vegetable seeds handbook. Regina seeds Seminis. 
Printed by Bizone ltd Nairobi, Kenya, 23 -25. 
Waiganjo, M.M., Kambo ,C., Kuria, S., Njeru, C., Mbaka, J., Gikaara, D., 
Amata, R., Erbaugh, M., Miller, S., Kyamanywa, S., Kleinhenz, M., 
Korach, J., Gathambiri, C., and Wepukhulu, S. (2011). On- farm grafting 
trials at Kangai tisa using new commercial tomato scion and wilt 
 tolerant rootstock (Mt56, Cherry tomato, Solanum incarnum and 
TKA).  
Wang, J. F., Chen, N. C. and Li, H. M. (1998). Resistance sources to Bacterial 
wilt in Eggplant (Solanum melongena). In: Bacterial wilt disease. 
Molecular and Ecological aspects. Prior, P., Allen, C. and Elphinstone, 
J. (Eds.), pp.284 – 289. Reports of the second International bacterial  wilt 
symposium held in Gosier, Guadaloupe, France, 22 – 27 June 1997. 
Wang, J. F. and Lin C. H. (2005). Integrated Management of Tomato bacterial 
wilt. Shanhua, Taiwan: AVDRC – The World Vegetable Center. 
Publication No.05 – 615. 
Wang, J. W., Park, M.Y., Wang, L. J.,  Koo, Y., Chen,  X.Y, Weigel, D. and 
Poethig, R. S. (2011). miRNA control of vegetative phase change in 
trees. PLoSGenet7(2):e1002012 
Weng, J.H. (2000). The role of active and passive water uptake in maintaining 
leaf water status and photosynthesis in tomato under water deficit. Plant 
Prod. Sci. 3: 296-298. 
Wiersinga, R., De Jager, A., Nabisiwa, A. and Kiragu, B. (2008). High 
segment report: 4 Final - Wageningen UR E- 
depot.http:/edepot.wur.nl/13874 Wageningen University NL. Retrieved 
22nd August, 2015. 
Wimer, A., Rideout, S. and Freeman, J. (2009). Management of tomato 
bacterial wilt on Virginia’s Eastern shore through Cultivar resistance and 
acibenzolar – S – Methyl applications. 
http://mbao.org/2009/proceedings/046wimer A San Diego summary 
1.pdf. Retrieved  22nd October, 2015 
 
107 
 
 
 
APPENDICES 
 
Appendix 1: Questionnnare 
 
BACTERIAL WILT QUESTIONNAIRE 
 
1. DETAILS OF THE RESPONDENT 
 
Date       Enumerator 
County      Sub-County  
Division 
LocatioN      Sub-location 
Farmers’ Name      Gender: Male       Female 
GPS Reading       Altitude  
Age categories 
 
2. VARIETY OF TOMATO GROWN 
 
Tomato 
(Rank in order of 
Preference) 
Acreage/No.of Plants 
1  
2  
3  
4  
5  
 
3. OTHER CROPS GROWN IN THE FARM 
 
 Tick Importance (1=Highly important, 2=important,3= 
Little Important) 
Maize   
Beans   
Sweet potatoes   
Arrow roots   
Bananas   
Cassava   
Tomato   
Others (specify)   
 
108 
 
 
 
a) Farm Ownership: Owned / Leased 
b) Do you have experience in tomato farming: Yes/No 
How many years have you grown tomatoes? 
c) What is the tomato production system? 
(i) Greenhouse 
(ii) Open Field 
(iii) Both 
d) Tomato planting materials 
e) Type of planting materials purchased: (seed or seedlings) 
f) Sources of planting materials  
[Own seed / seedlings] [Local nursery]  [Research institution]  
[Others...specify] 
g) Any challenges experienced with seed or seedlings? 
i. Diseases 
ii. Seedling vigour 
iii. Seed viability. 
iv. Trueness to type. 
v. Ecological adaptation? 
 
 
 
 
 
109 
 
 
 
4. TOMATO DISEASES/PESTS AND NUTRITIONAL 
DISORDERS (USE PHOTOCARD) 
 
a. Have you noted any of these diseases/pests/disorders on your 
tomato plants 
 
Disease/pest Currentl
y present  
 
Previously  
Observed 
Rank based 
severity/intensity: 
(1=highly severe,2= 
mild,3=low 
When 
noted 
Month/yea
r 
Bacterial wilt     
Bacterial pith 
necrosis 
    
Bacterial spot     
Early blight     
Late blight     
Verticillium wilt     
Damping off     
Blossom end rot     
Tomato Mosaic 
virus 
    
Powderly 
mildew 
    
Septoria leaf 
spot 
    
Stem canker     
Leaf mold     
Bacterial speck     
Gray mold     
Tomato yellow 
leaf curl 
    
Gray leaf spot     
Red spider Mites      
Whiteflies     
Aphids     
Nematodes     
Thrips     
Tuta 
absoluta(Leaf 
miner) 
    
Any other(fruit 
flies, termites) 
    
 
 
 
 
 
110 
 
 
 
5. MEASURES TAKEN TO MANAGE THE DISEASES 
(PREFERENCE:  BACTERIAL WILT). 
 
Measures 
taken 
Yes/No For which 
pests/disea
se 
Effectiveness 
   Highly  Moderate  Low  Not 
effective 
Field sanitation       
selection of 
seed or variety 
      
Pesticides       
Tool 
disinfection 
      
Removal of 
entire infected 
plant or plant 
part 
      
Applying 
nutrients 
      
Crop rotation       
Restricting 
entry to farm 
      
Restrict 
movement 
within the farm 
      
Any other 
measure(descri
be below) 
      
 
 
 
 
 
 
 
 
 
 
111 
 
 
 
6. INFORMATION ON INPUTS UTILISED 
a) Pesticide 
(i) What are the types and amounts of Chemicals used and their costs? 
Type 
(insecticide, 
fungicide, 
herbicide?) 
Trade 
Name 
Active 
ingredient 
Amount 
(Litre/Kg) 
Cost per 
litre/Kg 
(Ksh) 
Total 
cost 
(Ksh) 
1      
2      
3      
4      
5      
    TOTAL  
 
 
(ii) Have you received any extension advice on tomato production (on 
pests, diseases and control, or any other information)? 1= Yes ;2 = No 
 b)   Water 
(i). Do you irrigate? Yes/No 
(ii).What is the source of Water? River/Dam/Borehole 
(iii).Is the water used for irrigation treated? Yes/ No 
(iv).What is the method of irrigation? Sprinkler/Drip/Furrow/Basin 
  
112 
 
 
 
c)  Labour Management 
(i). What is the source of Labour? Family/ Hired 
( ii). If hired, how frequently do you hire?  
 Daily/weekly/monthly/during harvesting 
d) Machines/Tools 
(i). Do you use mobile machinery e.g.   
tractor/pumps/jembes/hoes/ploughs? Yes/No 
(ii). Are the machines owned or hired? 
(iii).If hired, at what cost? 
(iv). How often do you hire the machines?   
 Daily/weekly/monthly/during harvesting 
e) Fertilizer/manure application 
(i) Is fertilizer used organic or inorganic? 
(ii) Is manure used fully decomposed? 
7. FARM PRACTICES   
 a) Crop rotation 
 (i). Do you carry out crop rotation? Yes/ No  
  (ii). If yes, with what crop? Maize/beans/Kales/Cabbage 
  (iii). How long do you crop rotate? <3months/3-5months/5  
                   6months/>1year 
113 
 
 
 
b) Field hygiene 
 (i). How do you manage crop residues in the farm? Bury/Burn/feed the 
livestock/throw   
(ii). How often do you ensure that field hygiene is maintained? 
Weekly/Monthly 
 c) Disinfection 
 (i). Do you have disinfectant at entry to the greenhouse? Yes/No 
 (ii).Do you disinfect tools used in the farm? Yes/No 
(iii). What kind of disinfectant do you use? 
(iv). How often do you disinfect? 
 
 
 
 
 
 
 
 
114 
 
 
 
8. FIELD OBSERVATION 
Assessment of general agronomic and farm management practises on 
tomato farming (researcher 
 
to observe and assess this on a 1 - 5 scale; 1=poor; 5 = best). 
 
Practice  Tick if done Score  
Desuckering   
Weeding (indicate manual/herbicides)   
Removal of infected plants   
Manure application   
Watering    
Plant protection measures   
Other practises (if any; specify)   
   
Presence of diseases and pests Tick if 
present  
Score (incidence/ 
severity) 
Bacterial wilt   
Early blight   
Late blight   
Brown spot   
Damping off   
Blossom end rot   
Tomato Mosaic virus   
Powderly mildew   
 
 
Rank the Following Constraints in Order of Importance in Tomato 
Production 
 
Constraint  Rank  Propose a solution 
Scarcity of planting materials   
Pests and diseases   
Declining soil fertility   
Market access and prices   
Poor transport system   
Inadequate extension support   
Drought/water scarcity   
Lack of information   
Lack of pesticides and fertilizers   
High cost of inputs   
Scarcity of farming land   
 
 
115 
 
 
 
Appendix 2: PHOTO card 
Some of tomato diseases 
      
Bacterial wilt disease                             Early blight on leaves 
    
Late blight on leaves   Blossom end rot on tomato fruit 
      
 
Blossom end rot on unripe tomatoes   Damping off on tomato seedling  
 
116 
 
 
 
          
Verticillium wilt on tomato plant          Tomato yellow leaf curl virus 
Some of Tomato pests 
         
Tuta absoluta effect on tomato 
       
Tuta absoluta on tomato fruit    White flies 
 
 
 
 
 
117 
 
 
 
Appendix 3: ANOVA Tables 
Objective 2: Identification of bacterial wilt resistant germplasm for use as 
rootstocks 
The data analysed is for disease incidence of the bacterial wilt cultivars to be 
used as rootstocks in tomato grafting. 
 Appendix 3a (7 days). 
Source of 
variation d.f. s.s. m.s. F P 
Rep stratum 2 0 0     
Treatment 5 0 0     
Residual 10 0 0     
Total 17 0       
 
Appendix 3b (14 days) 
Source of 
variation d.f. s.s. m.s. F P 
Rep stratum 2 0.3333 0.1667 0.24   
Treatment 5 25.1667 5.0333 7.19 0.004** 
Residual 10 7 0.7     
Total 17 32.5       
 
Appendix3c (21 days) 
Source of 
variation d.f. s.s. m.s. F P 
Rep stratum 2 0.111 0.056 0.04   
Treatment 5 94.278 18.856 14.26 <.001*** 
Residual 10 13.222 1.322     
Total 17 107.611       
  
 
 
 
118 
 
 
 
Appendix 3d (35 days) 
Source of 
variation d.f. s.s. m.s. F P 
Rep  2 0.4444 0.2222 0.4   
Treatment 5 46.4444 9.2889 16.72 <.001*** 
Residual 10 5.5556 0.5556     
Total 17 52.4444       
 
Objective 2: Determination of compatibility of bacterial wilt resistant 
rootstocks to preferred tomato varieties 
a) Proportion (%) of grafted plants fully healed /established fourteen 
days after grafting 
Source of variation d.f. s.s. m.s. F P 
Rep  2 1.4444 0.7222 0.92 
 Treatment 5 18.2778 3.6556 4.63 0.019* 
Residual 10 7.8889 0.7889 
  Total 17 27.6111   
   
b) Height of grafted transplanted plants 
Source of variation d.f. s.s. m.s. F P 
Treatment 5 749.83 149.97 7.43 <.001*** 
Residual 18 363.5 20.19     
Total 23 1113.33       
 
c) Yield of grafted transpanted plants 
Source of variation d.f. s.s. m.s. F P 
Treatment 5 77.21 15.44 0.62 0.687 
Residual 18 448.75 24.93 
  Total 23 525.96 
    
 
 
119 
 
 
 
d) Height of grafted inoculated and uninoculated plants 
Source of variation d.f. s.s. m.s. F P 
Rep stratum 1 11.41 11.41 0.8   
Inoc_status 1 12.74 12.74 0.89 0.365 
Treatment 5 220.89 44.18 3.1 0.055 
Inoc_status.Treatment 5 27.05 5.41 0.38 0.852 
Residual 11 156.62 14.24     
Total 23 428.72       
 
e) Yield in grams of grafted innoculated and uninoculated plants 
Source of variation d.f. s.s. m.s. F P 
Rep stratum 1 1.475 1.475 0.72   
Inoc_status 1 0.08 0.08 0.04 0.848 
Treatment 5 8.175 1.635 0.79 0.576 
Inoc_status.Treatment 5 8.035 1.607 0.78 0.585 
Residual 11 22.682 2.062     
Total 23 40.447       
 
Objective 4: Stage of growth 
Source of variation d.f. s.s. m.s. v.r. F pr. 
Rep stratum 2 4.2222 2.1111 3.22   
Stage 1 90.25 90.25 137.46 <.001*** 
Treatment 5 24.8056 4.9611 7.56 <.001*** 
Stage.Treatment 5 4.5833 0.9167 1.4 0.264 
Residual 22 14.4444 0.6566     
Total 35 138.3056