PHD-Department of Plant and Microbial Sciences

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Interactions among leafhopper vector populations, maize streak virus disease, altitude and soil fertility
(2011-08-03) Magenya, Oscar Enos
Leafhoppers of the genus Cicadulina exclusively transmit Maize streak virus (MSV) disease which is an important constraint to maize production in Sub-Saharan Africa. Current literature indicates that agro-ecological factors influence leafhoppers and the MSV, but no information is available on the influence of altitude and soil nutrients on Cicadulina spp. and the MSV disease, and how these factors can be manipulated for disease control. The leaffhopper populations and the viral strains that they transmit were assessed to determine the geographical distribution and the prevalence of the MSV disease. Farm interviews, insect vector end soil sampling were carried out in six study regions to determine the level of farmer perception, leafhopper species distribution and soil nutrient levels in the regions. The selected regions were Bahari, Mwea, Githunguri, Oyani, Muhoroni and Kimilili in Kenya. The results indicated that farmers in Mwea and Oyani regions incur high yield losses of more than 40% due to M'W disease. Between 7% and 30% of farmers apply inorganic fertilizers, although the different s were not significantly different. The species of leafhoppers identified in the regions included cicadulina mbila Naude, C. storeyi China, C. chinai Ghauri and C. bipunctata (Melchar). The population sizes of the various Cicadulina species differed significantly (p = 0.021 and j = 0.006 respectively). Regression analysis showed that C. mbila numbers decreased significantly with altitude, and C. mbila correlated negatively with altitude. Most regions showed inadequate levels of phosphorus for plant growth, and the level of nitrogen and potassium differed significantly between the regions (p < 0.01). The viral isolates transmitted by C. mbila fro n Oyani region caused significantly higher percent disease incidence (87 %) than that from ( Githunguri, Muhoroni and Bahari regions (63, 60 and 53 % respectively). Screen house studies indicated that significantly low number of plants with MSV symptoms were recorded after high nitrogen treatment (75 kg N ha 1), compared to the rates of 0, 25 and 50 kg N ha 1. Plants that received 75 and 25 kg P ha treatments were significantly taller than those that did not receive any treatment. Nitrogen fertilizer correlated positively with the number of insects settling on the treated maize plants (r = 0.614; p < 0.011). Nymphal survival was significantly lower on the 25 Kg N treatment. However, plants treated with 25 kg N had comparatively higher percent lignin, and tannins, although differences of the later two were not significant. Pair wise correlation matrix analysis indicated that nitrogen treatment correlated positively with the percent nitrogen present in maize plant tissues, negatively with the neutral detergent fibres (r = - 0.510; p = 0 )43) and positively with the number of surviving nymphs (r = 0.502; p = 0.047). Acid detergent fibres correlated positively with the percent lignin (r = 0.815; p = 0.001). In addition, no significant relationship between the longevity of both male and female leafhoppers and the rate of phosphorus treatment was indicated. The findings of this study suggest that the application of, different rates of nitrogen and phosphorus fertilizers influence leafhopper behaviour and consequently the expression of MSV disease. This information can be used by the fertilizer industry to reformulate fertilizers, particularly for use in the management of vector borne diseases. Further research to design experimental systems of investigating responses of leafhoppers to global environmental changes is proposed. Such a study would assist in mitigating the effects of environmental change within the contest of establishing appropriate fertilizer regimes for crop production
Nitrogen fixation in promisccuous soybean (Glycine Max (1.) Merril) varieties in Eastern Kenya
(2011-08-15) Maingi, J.M.; Gitonga Mburugu; Shisanya, C.A.; George Muluvi
Soybean (Glycine max (L.) Merril) is referred to as the golden crop of the future. It contains approximately, 40% proteins, 20% oil, 14% carbohydrates, various minerals and vitamins. Approximately 70,000-100,000 tonnes of soybean are required in Kenya with only 5,000 tonnes produced locally and the rest imported. Human consumption is expected to rise ten-fold in the next ten years. The number of soybean producers is still small and fragmented across the country. The small scale farmers in Kenya are resource poor and cannot afford the expensive inputs in terms of nitrogen fertilizer to increase soybean production. The farmers do not also make use of inoculants that provide an alternative and cheaper source of nitrogen for crop production than the N fertilizers. Soybean crops as are grown by farmers receive no inoculants and little or no commercial nitrogen fertilizer. To avoid this need for inoculation, soybean breeders in the International Institute of Tropical Agriculture, Nigeria developed new soybean genotypes for Africa. These genotypes known as tropical glycine cross (TGx) nodulate with Bradyrhizobium sp. population indigenous to African soils. These genotypes have been tested in some parts of Africa with great success. However, the TGxs have not been tested in Kenya. The main objective of this study was to investigate nitrogen fixation in promiscuous soybean varieties in two different agroecological zones in eastern Kenya. About fifty different isolates were obtained from the two study sites Kiboko, south east Kenya and Kaguru in east Kenya. About 20 % of the isolates were slow growers while 80 were fast growers. Four different rhizobia groups were identified upon restriction of the DNA of the isolates with Msp I and Hae III. Isolates, M8, M10, M12, M20 and M22 were identified as being potential source of effective inoculum for soybeans in the study areas. The results of Most Probable Number counts indicated that the total bradyrhizobia population in Kiboko was between 2.59x104 and 1.89x105 per gram of soil. In Kaguru, the approximate total bradyrhizobia was between 1.04x102 and 7.56x103 per gram of soil. The population size of taxonomically defined slow growing rhizobia in Kiboko was between 2.59x102 and 1.89x103 cells per gram of soil while in Kaguru, the population was between 1.33x102 and 9.72x102 cells per gram of soil. The approximate rhizobia population specific to TGx genotype in Kiboko was between 7.81x102 and 5.67x103 while in Kaguru, the population was between 2.37x102 and 1.73x103 cells per gram of soil. In terms of crop performance in field conditions, TGx varieties and Magoye performed better than Nyala and Gazelle in all the parameters that were assessed. From this study, persistence of introduced commercial inoculant, Bradyrhizobium japonicum USDA 110 in the two study sites was also evident. Inoculants can be a potent alternative to chemical nitrogen fertilizer as well as a renewable resource that is capable of sustaining food production with little purchased inputs. The small scale farmers in the two study sites are resource poor and will benefit a lot by using this cheaper technology to boost soybean production
Indigenous knowledge and effects of integrated soil fertility management on growth, grain yield and rhizobia genetics of selected cowpea varieties
(2011-08-15) Kimiti, Jacinta Malia
The main objectives of this study were; (1) To find out whether farmers in Makueni District were aware of soil fertility status in their farms and annual food availability, (2) To find out the proportions of cultivated areas under grain legume production and the problems faced by farmers in grain legume production, (3) To screen and select high yielding cowpea varieties for dryland Makueni District, (4) To determine the effects of integrated soil fertility management (ISFM) on nodulation, growth and grain yield of selected cowpea varieties, and (5) To determine the effects of ISFM on nitrogen fixation, indigenous soil rhizobia populations and rhizobia diversity. Farmer participatory meetings were used to establish whether farmers recognized soil fertility as a problem in legume production. Results obtained revealed that farmers in the selected sites recognized soil fertility as a problem and included it in the list of general problems affecting them. Participating farmers indicated that only 2% of the cultivated farms in the study sites had fertile soils. To document grain yields, area under legume cultivation and problems faced by farmers in grain legume production, a structured questionnaire was used to collect information from farmers. Results obtained showed that grain yields ranged from 30 kg/ha to 416 kg/ha and area under legume cultivation from 48% to 92%. Problems faced by farmers in legume production included low soil fertility, inadequate farm inputs, weeds, pests and diseases. To select pioneer cowpea varieties, 34 cowpea varieties were selected and screened for two seasons at Kiboko Dryland Research Station. Some of the cowpea parameters assessed included pod length, plant biomass, grain yield and weights of 100 seeds. From the screening studies, nine cowpea varieties were selected for on-farm trials. To determine the effects of integrated soil fertility management (ISFM) on nodulation, growth and grain yield of selected cowpea varieties, on-farm trials were established at two sites. The nine cowpea varieties that had been selected during the screening studies were planted in the trials. Treatments applied included a control, farmyard manure at 2.5 t/ha, phosphorus as triple superphosphate (TSP) (P205, 0:46:0) at 15 kg/ha and a combination of both manure and TSP at the singly applied rates. Data collected included nodule and shoot biomass, and grain yields. Results obtained revealed that treatment application enhanced nodule and shoot biomass, and grain yields. Nitrogen fixation was estimated using 15N natural abundance method while rhizobia populations were determined using most probable number (MPN) experiment. Rhizobia diversity was determined using culture characterization and direct PCRRFLP of the 16S-23S rRNA intergenic spacer region (IGR) of rhizobia genome. Results of nitrogen fixation showed that 46-53% nitrogen (N) was fixed at a wetter site, while no N fixation took place at a drier site. Results from rhizobia population assessment revealed population counts of 4.89x102 to 2.0x104 cells/gram of soil with lower rhizobia counts at planting relative to the harvesting time while high rhizobia counts were recorded in amended soils relative to the controls. Further, restriction of eighteen rhizobia isolates from cowpea nodules with MspI restriction endonuclease revealed four rhizobia IGS groups
Geographic variation in the development of cotesia sesamiae (hymenoptera: braconidae) on Busseola fusca (lepidoptera : noctuidae) in Kenya: polydnaviruses and co-evolutionary dynamics
(2011-12-07) Gitau, Anne Catherine
Microgastrine endoparasitoids co-inject symbiotic viruses known as polyDNAviruses (PDV) together with other wasp factors such as the venom and calyx fluid proteins during oviposition in hosts. These factors disrupt the host immune system allowing the parasitoids to develop successfully. In Kenya, the endoparasitoid Cotesia sesamiae (Cameron) (Hymenoptera: Braconidae) exists as two biotypes that differ in their ability to parasitize the stem borer Busseola fusca (Lepidoptera: Noctuidae). Cotesia sesamiae from western Kenya completes development in B. fusca larvae hence it is virulent. The coastal C. sesamiae biotype does not complete development and eggs oviposited get encapsulated in B. fusca larvae, and therefore it is avirulent. It is not yet known if intermediate C. sesamiae populations exist between western and coastal Kenya. On the other hand, several B. fusca biotypes have been described recently and it is not clearly understood whether this host also contributes to variation in C. sesamiae parasitism. In this study, B. fusca acceptance and suitability of different strains of C. sesamiae were examined. The avirulent strains were reluctant to oviposit in B. fusca larvae while the virulent strain readily oviposited in this host. Egg loads of the virulent C. sesamiae from Kitale were significantly lower compared to those of the avirulent Mombasa and Taita C. sesamiae females. Development of C. sesamiae in B. fusca larvae was tested in an interaction matrix. Results showed that both C. sesamiae and B. fusca contributed to the variation in the parasitoids' success. 39% of the variation was attributed to the geographic locality of C. sesamiae, 35% by the host locality and 27% by their interaction. Geographic variation in successful parasitism of hosts by their parasitoids was attributed to the co-evolutionary dynamics and selection pressures in C. sesamiae local community. Results from this study showed that the avirulent C. sesamiae strains have been under selection pressure to evolve a system that suppresses B. fusca 's immune reaction. The CrV 1 gene homolog was tested on various C. sesamiae strains using Polymerase Chain reaction (PCR). The CrV 1 gene was present in all the C. sesamiae strains. However, restriction enzyme tests showed that the gene is differently organized in the virulent and the avirulent C. sesamiae strains. The CrV 1 gene expression was found in fat bodies and haemolymph tissues of B. fusca larvae using the Reverse Transcriptase-PCR (RTPCR). Results showed that this gene was expressed in the fat bodies and haemolymph tissues of B. fusca and S. calamistis parasitized by the virulent C. sesamiae strains. For the avirulent C. sesamiae strains, CrV 1 gene expression was only evident on the permissive host S. calamistis but not B. fusca tissues. Differences in calyx fluid contents of the virulent and avirulent C. sesamiae populations were evaluated using the 2D-gel electrophoresis and results showed that more protein spots were present in calyx fluid of the virulent C. sesamiae than that of the avirulent strain. Changes in protein profiles in B. fusca larvae parasitized by the two C. sesamiae strains was evaluated by SDS-PAGE gel on fat body and haemolymph tissues. Results showed parasitism-specific protein bands in both tissues parasitized by the two C. sesamiae strains.
Role of wild host plants in population dynamics of cereal stemborers and the associated parasitoids in Uganda
(2011-12-13) Matama, Teddy Kauma
Lepidopteran stemborers attack several graminaceous and wild host plants. These pests are one of the major constraints to maize production in Africa. However, efforts to control stemborers have aimed at cereal crops and the role of alternative wild hosts has been neglected. Recent reports have indicated that the abundance of wild grass in the maize field surroundings is correlated with lower stemborer incidence. This study was conducted with the aim of elucidating the role of wild grasses in stemborer infestations in maize in Uganda. To achieve this goal, surveys, field and screen house trials were conducted between 2003 and 2005. The study covered four Agroecological zones and these included the Eastern, South eastern, Lake Victoria Crescent and Lake Albert Crescent ecozones. Results showed that mainly four stemborer species occur on maize in Uganda. Busseola fusca Fuller (Noctuidae) and Chilo partellus (Crambidae) were the most important across the four Agroecological zones (AEZs). The distribution of these stemborers varied across AEZs with C. partellus as the major stemborer species in the eastern AEZ while B. fusca was dominant in the Lake Albert Crescent. The major parasitoids of these stemborers were the introduced Cotesia flavipes and the indigenous Cotesia sesamiae Cameron (Braconidae) attacking the larval stage and Dentichasmias busseolae Heinrich (Ichneumonidae) and Procerochasmias nigromaculatus Cameron (Ichneumonidae) that attacked the pupal stage. Surveys of stemborers on the selected grasses revealed that wild sorghum Sorghum arundinaceum (Desv.) Stapf. was the major wild host plant for B. fusca and C. partellus and these stemborers were not common on the wild grasses Panicum maximum Jacq., Pennisetum polystachion (L.) Schult. and Pennisetum purpureum Schumach. However, these grasses were hosts of many stemborer species that are confined to the wild grasses. Host plant preference studies showed that all the four selected grasses studied were not preferred over maize for oviposition by both. C. partellus and B. fusca. These grasses did not support larval development to pupation except for S. arundinaceum, which had high numbers of C. partellus pupating although with reduced weights compared to maize. Therefore, amongst the grasses tested, S. arundinaceum was found to be a suitable host for the development of C. partellus and B. fusca, and may form a reservoir during the off-season for both the pest and parasitoids as several parasitoid species were recovered from this grass species. C. sesamiae was also frequently recovered from P. purpureum indicating that this grass species also forms a reservoir for this parasitoid and C. flavipes to a small extent. Results further showed that wild grass border rows did not have a consistent effect on reducing stemborer infestations and larval parasitism was independent of the grassy borders. The role of grassy border rows in controlling cereal stemborers in crops is not well understood. Leaving wild grasses intact in the vicinity of crop fields might have a greater effect on stem- borer populations in crops than planting grassy border rows around the fields. There is also need to understand better the mechanisms for reduced pest densities when grasses are growing in the vicinity of cereal crops. The role of grasses in maintaining parasitoids need to be further investigated and perhaps grasses that enhance parasitism with out necessarily increasing pest infestation be identified.
Stemborer parasitism by Cotesia sesamiae and strurmiopsis parasitica and an assessment of the need to introduce cotesia flavipes into zimbabwe
(2012-01-03) Chinwada, Peter; Mueke, J. M.; Overholt, W. A.
Stemboreres are major pests of maize and sorghum in Zimbabwe. An analysis of the research work on cereal stemborers in the country revealed several gaps for which information is required. Thus, as a way of bridging the identified information gaps, the studies reported in this thesis were conducted mainly to provide information on the distribution, abundance and seasonal occurrence of stemborers and their natural enemies, parasitoid seasonal carryover mechanisms and parasitoid biology, and to assess the need for the introduction of the exotic larval end parasitoid Cotesia flavipes Cameron (Hymenoptera: Braconidae). The seasonal occurrence of cereal stemborers and their natural enemies was studies for three seasons (1999-2000, 2001-01) within the highveld (>1200M), middleveld (600-1200m) and lowveld (<600m) ecological zones of Zimbabwe. Three species of stemborers were recorded, namely, Busseola fusca Fuller (lepidoptera: Noctuidae), Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) and Sesamia calamistis Hampson (Lepidoptera: Noctuidae). Chilo partellus was the most abundant and widely distribute species, occurring at all sites, but predominantly in the lowveld and middledveld. Busseola fusca was the second most abundant species but predominated only in the highveld. Sesamia calamistis, on the other hand, appeared to be an uneconomic pest due to its overall low frequency of occurrence. Stemborer natural enemies recorded included the larval parasitoids, Cotesia sesamiae (Cameron) (Hymenoptera: Braconidae) and Sturmiopsis parasitica (Curran) (Diptera: Tachninidae), the egg-larval parasitoid, Chelonus curvimaculatus Cameron (Hymenoptera: Braconidae), the pupal parasitoids, Procerochasmias nigromaculatus Cameron, Dentichasmias busseolae Heinrich (both Hymenoptera: Ichneumonidae) and Pediobius Furvus Gahan (Hymenoptera: Eulophidae), and an entomogenous nematode, Hexametric sp. (Mermithidae). While C. sesamiae had a much wider distribution and host range, S.parasitica occurred only within the highveld (Harare area) where it parasitized B. fusca. Outside the highveld, C.sesamiae was, however, not recovered at Muzarabani (lowveld) and also appeared to be scare at Bushu (Middleveld). In the Harare area, S. parasitica parasitism predominated for about half of the season (December-February) and attained a peak (10.9-60.2%) between the end of January and mid-February. Thereafter, parasitism declined sharply and by the end of March, recoveries of S. parasitica had all but ceased. In contrast, C. sesamiae parasitism generally fluctuated between 0 and 20% for the remainder of the season. Sturmiopsis parasitica over wintered in disapausing larvae from which it emerged in October-December when host diapause was terminated. In contrast, the seasonal carryover mechanism of C. sesamiae could not be identified. Laboratory experiments were conducted to evaluate B.fusca, S.Calamistis and C. partellus for their acceptability and suitability as hosts to a highveld and a lowveld C. sesamiae population. Both C. Sesamiae populations preferred the noctuids to C.Partellus for oviposition, possible reflecting differences in evolutionary history. However, the three hosts showed differential suitability for the development of the two C. sesamiae population. Whiles all were suitable for the development of the highveld. C.sesamiae, B.fusca was a partially suitable host to the lowveld population. Crosses between the highveld and lowveld. C. Sesamiae adults were compatible, producing mixed sex progenies. Based on the results of the host suitability and mating compatibility studies and a knowledge of the maize growth cycles within the different ecological zones, it is postulated that one probable. C. Sesamiae seasonal carryover mechanism in Zimbabwe could be a yearly net outward migration of the parasitoid from lowveld ''ecological islands'' to niches where populations die out each year due to a long dry season and the consequent diapause-induced host unavailability. On its own, however, sustenance of C. sustenance of C. Sesamiae in such ''ecological islands'' is not a satisfactory carryover mechanism thus other possible mechanisms need tobe investigated. The development and levels of parasitism of S. parasitica on B. fusca, S.calamistis and C. partellus were studied in the laboratory. Parasitoid puparia recoveries were much higher on B.fusca 983.3% parasitism) than on C. partellus (15% parasitism). No development occurred on S. Calamistis due to maggot encapsulation. At 25±0.50C, parasitoid larval developmental period on non-diapause B. fusca larvae averaged 14.2 days and the pupal period ranged from 13.7 days (males) to 15.8 days (females). Maggots’ were first observed at 6 days after mating and their numbers peaked (537-848 per female) after a 10-16 day gestation. Inoculation of diapausing B.fusca larvae resulted in a greatly extended larval period. Thus, the observed seasonal carryover mechanism of s. Parsitica is simply a replication of host hormonal influences on the parasitoid's larval developmental duration in diapausing as opposed to non-diapausing host larvae. The suitability of B. fusca and C. partellus for development of the exotic parasitoid, C. flavipes, was investigated in Zimbabwe. Although C. flavipes accepted both stem borer species for ovipositor, development was only completed on C. partellus. Busseola fusca was an unsuitable host due to egg encapsulation. While this confirms the suitability of C.partellus for development of the exotic parasitoid, the apparent absence or very low impact of the indigenous C. sesamiae at some of the C. partellus ''hotspots'' further highlight the need to release C.flavipes in the country
Bioecology and population dynamics of red spider mites( a cari: tetranychidae) on tomato in small scale production systems in Kenya
(2012-01-03) Sarr, Ibrahima
Tomato, Lycopersicon esculentum Mill. (Solanaceae) is one of the most important vegetables grown in Eastern and South Africa for local consumption and income generation by small scale farmers. Yet, yields of the crop are far below the potentials due to many factors including damage caused by red spider mites. This is aggravated by unsustainable control strategies relaying solely on highly toxic pesticides with long term harvest intervals and subsequent contamination of human and the environment. Sustainable and environmentally friendly integrated production and pest management approaches are therefore urgently required. This study aimed at providing basic information on the bioecology and the population dynamics of red spider mite, Tetranychus evansi pritchard and Baker and the two spotted red Spider mite, Tetranychus urticae Koch appeared to form the acarine complex in field tomatoes in Kenya. In laboratory life table studies, T. evansi, the most damaging red spider mite on tomatoes showed a high potential of increase at 30°c with a short overall developmental time from egg-to-adult of 8.82±0.21 days, a more female biased sex ratio of 1.75 female per male despite a low hatchability of the eggs. None of the female deutonymphs emerged at 100°c and a significantly slower overall developmental time from egg-to-adult of 55.13±2.83 days at 15°C (p<0.05) was recorded. The lower thermal developmental threshold for T. evansi was 12°C. The spatio-temporal and within plant distribution patterns of the two spotted red spider mite, T.urticae revealed the lower tomato canopy layer as the preferred zone for these spider mites. Furthermore, T. urticae was a very aggregative species. The preliminary sampling plan derived from this aggregative distribution patterns showed that a precision of 0.25 ( a ration of mean to standard error) was reasonable and still adequate for the density estimate of T.urticae adults in field tomatoes. The study carried out on the effect of the predators on T. Evansi, showed that five species of predators were associated with T. Evansi,and included; Phytoseiuhus persimilis Athias -Henriot (A cari: Phytoseiidae), Pronematus spp. (A cari: Tydeidae), Oligota spp. (Coleoptera: Staphylinidae) and Stethorus spp. (Coleoptera: Coccinellidae) However, these predators did not seem to have any impact on the population of T. evansi. An intensive regression analysis and a graphical description carried out between the T. urticae rate of increase, the plant quality, the predators and the weather data from three tomato growing seasons revealed that, the plant quality was positively associated with the rate of increase, while rainfall and temperature relative humidity interaction showed a negative relationship with the rate of increase. Further more, the stepwise regression between the rate of increase, the plant quality, the predators and the weather data showed that 40% of the variation in red spider mite numbers over the three growing seasons was explained by the biotic factors and weather condition. The population dynamics was a function of the initial level of infestion and the rate of increase
Carbon budget and sustainable harvesting of cyperus papyrus L. (Papyrus) in a papyrus swamp in lake Naivasha, Kenya
(2012-02-14) Kariuki, Francis Wachira
Carbon budget and sustainable harvesting of Cyperus papyrus (papyrus) in a papyrus swamp in Lake Naivasha were investigated. Carbon dioxide fluxes and photosynthesis were measured using eddy covariance and IRGA techniques respectively. Sustainable harvesting was assessed using five treatments, control, harvesting at intervals of 6, 12, 24 and 36 months each replicated five times in a Latin Square Design Carbon sequestration in the swamp was investigated through decomposition using litterbag and analysis of swamp components for carbon and nitrogen. Light compensation point was reached at PAR value of 1200 m-2s-1 between 08.00 and 09-00 hours. Mean maximum midday CO2 uptake was -24.40 ± 1.36 mol m-2s-1 corresponding peak PAR (1882 mol m-2s-1) with -31.19 and -18.92 mol m-2s-1 as the highest and the lowest uptake values respectively for days with monomodal peaks. On those days with bimodal peaks, the initial peak was -24.87 ± 9.29 mol m-2s-1 between 11.00 and 12.00 hours and a second peak at about 14.00 hours of -29.29 ± 1.27 mmol m-2s-1. Mean CO2 efflux was 10.28 ± 1.38 mol m-2s-1. Mean water vapour flux were 0.00 and 8.25 mmol ± 1.27 mmol m2s-1 for night and day respectively. The day peak corresponded to peak PAR, temperature and sensible heat. Papyrus had a maximum assimilation rate of 68.7 umol m-2s-1 and Carboxylation Efficiency (CE) of 0.06 compared to assimilation rate of 36.7 umol m-2s-1 and CE of 0.02 in Cyperus immensus. However, C. papyrus was CO2 saturated at a lower internal carbon dioxide concentration that C. immensus (C4), an indication of intermediate characteristics. Papyrus above ground biomass and culm density at 6 months harvesting interval showed significant (P<0.05) difference in terms of harvesting intervals. The overall culm density for six months intervals was 7.78±1.33 initial, 11.66 ± 2.55 and 11.62 ± 5.94 during the second and third harvest intervals respectively. This insignificantly declined (P>0.05) TO 10.66 ± 2.89 when the fourth harvest was delayed by three months and declined significantly (P<0.05) further to 4.98 ± 1.65 on the fifth harvest. The 12 months intervals showed the overall density increasing insignificantly (P>0.05) from initial 6.04 ± 2.35 to 9.36 ±2.46 at the second harvest. This declined significantly (P<0.05) to 7.42± 2.04 at the time of the third harvest. The above ground biomass showed an initial significant (P<0.05) decreased to 1087.64 ± 695.10 from 3290.52 ± 637.04 and thereafter significantly (P<0.05) increased to 1773.18 ± 496.27 gm-2 upon the third harvest. This was an indication that papyrus biomass was not density dependent. With the 24 months interval, the overall density showed a fairly stable state with density of 10.07 ± 1.99 and 11.18 ±1.73 culms m-2 initial and second harvests respectively. The results show that the rate of recruitment was approximately equal to that of mortality indicating a stable community. The above ground biomass significantly (P<0.05) increased from initial 2697.61±597.60 ±818.89 gm-2 a 25% increase. Decomposition was found to vary with the position (habitat) of litter at the site. The percentage material remaining after 300 days of decomposition was 74.05, 73.76 and 86.54 under the detritus, in water and on the detritus respectively. The decomposition rates after 90 days were 0.36, 0.81 and 1.02 and, the half-life were 3.94, 1.87 and 1.94 on the detritus, in water and under the detritus respectively. Analysis of papyrus plant organs and swamp components showed that percentage carbon was highest 47.92 ± 0.25 in the umbels and lowest 43.86 ± 0.63 in roots. Percentage carbon was 44.29± 0.18 in culms, and 47.08 ± 0.15 in rhizomes. Detritus and peat had percentage carbon of 37.95 ± 2.30 and 18.23 ± 0.23 respectively. Percentage nitrogen content was least 0.329 ± 0.02 and highest 1.297 ± 0.04 in the roots. Culms had 0.934 ± 0.04 while rhizomes had 1.219 ± 0.06% nitrogen content. The whole plant had 45.85± 1.92 and 1.14 ± 0.15% carbon and nitrogen contents respectively and C: N ration of 40:1. In detritus and peat, percentage nitrogen contents were 1.84 ± 0.14 and 0.977 ± 0.08 respectively. In terms of C:N ratio, the highest among the plant organs was 134:1 in senescent culms and least 34:1 in roots and 39:1 and 43:1 in rhizomes and umblels respectively and, 47:1 in culms. It was 19:1 and 21:1 in peat and detritus. This shows that the C:N ratio for papyrus organs was significantly (P<0.05) higher than the 17:1 dietary requirement of proteins for most animals. Carbon exchange indicates that papyrus swamps are presently sources of carbon. This status can be reversed through sustainable harvesting, which in the short term will be a source of carbon but will reverse once the amount of detritus is substantially reduced. Sustainable harvesting was found to be possible at 24 months intervals.
An ethnopharmacological investigation of plants used by Abagusii traditional medical practitioners
(2012-03-07) Gisesa, Nyangate Obiero
An ethno-medical survey of plants used by Abagusii Traditional Medical Practitioners was carried out and 166 plant species representing 138 genera and 62 families were botanically identified. Antimicrobial and phytochemical screening of 20 plants selected from the survey, and reputed to be widely used in the treatment of infectious diseases, was carried out. The various plant parts (roots, stems, leaves and flowers) of one of the medicinal plants, Euphorbia hirta L. were Sohxlet extracted with three solvents in order of increasing polarity (ether, methanol and water). The solvent with the most active extracts (methanol) was used for subsequent extractions of the rest of the plants. The extracts were screened for bioactivity using the disc diffusion method. Using the same method representative organisms were screened to represent a broad spectrum of microorganisms including specific clinical isolates from Kenyatta National Hospital. Tests were performed using the selected plant extracts to find out how effective individual extracts were against specific human pathogens. The phytochemcal screening was done by the use of successive and selective extractions with solvents of different polarities (ether, methanol and water). The screening covered mainly nitrogenous compounds, acetogenins, polyketides, isoprenoids and carbohydrates. In the antimicrobial screening it was found that most of the plant extracts inhibited the growth of the 7 bacterial species, the fungus and the majority of the 13 pathogenic micro-organisms that they were tested against. In the phytochemical screening 12 plants (60%) gave a positive reaction for alkaloids, 14 plants (70%) tested positive for tannins, 12 plants (60%) tested positive for flavonoids, 17 plants (85%) tested positive for coumarins, 9 plants (45%) tested positive for polyketides(emodin), 7 plants (35%) showed the presence of anthocyanins, 7 plants (35%) tested positive for anthracene glycosides and 6 plants (30%) showed the presence of fatty acids, 17 plants (85%) showed the presence of steroids/triterpenoids, 13 plants (65%) tested positive for saponins, 17 plants (85%) tested positive for volatile oils and 10 plants (50%) showed the presence of carotenoids, 9 plants (45%) showed the presence of polyuronoids, 11 plants (55%) tested positive for polyoses while 2 plants (10%) showed a positive reaction to starch.and 18 plants (90%) tested positive for reducing compounds. The results show that the local flora has a diversity of plant species with potential medicinal value. The results also confirm that there is credence to a number of uses to which herbalists put in certain plants and their use in traditional medicine and that the plants used by Abagusii Traditional Medical Practitioners are effective against pathogenic micro-organisms. The results supported the hypothesis that the plants used by the Abagusii Traditional medical practitioners have compounds of curative value and therefore they play an important role in the basic health care of these people
Cross-stage physiological effects of the desert locust, schistocerca gregaria, aggregation pheromones on their behaviour and susceptibility to control agents
(2012-03-07) Kane, Mohamed Habib
The desert locust, Schistocerca gregaria (Forskal, 1775) (Orthoptera: Acrididae) is a voracious and polyphagous pest of worldwide importance. Locust control relies on repetitive application of insecticides, rendering this option expensive and environmentally-damaging. New locust control initiatives emphasise the use of botanicals, entomopathogens, Insect Growth Regulators (IGRs), and pheromones. Phenylacetonitrile (PAN), the major and key component of the aggregation pheromone of older male adult desert locusts showed deleterious effects on conspecific nymphs. The nymphal pheromone blend (NPB) de-aggregated conspecific adults and lead gravid females to disperse their eggpods. However, the optimum use of PAN and NPB on desert locust control has not been investigated yet. The aim of this study was to optimise the use of PAN in enhancing susceptibility of S. gregaria nymphs to fenitrothion and neem oil and assess the effects of nymphal pheromone blend (NPB) on conspecific adults. The whole work was carried out under laboratory conditions. The results showed that desert locust nymphs were sensitive to all carriers that were tested [Tween 20, paraffin oil, polyethylene glycol 200 (PEG 200), paraffin oil, cyclohexanone], either applied topically or in vapour form regardless of the monitored parameters including food uptake, grouping behaviour and walking behaviour. Comparison of two modes of application of PAN showed that the release of PAN from a vial with a vent of 2 mm on its cap was significantly more effective in reducing the food uptake compared to their respective controls than its release from impregnated cotton roll. However, in both cases, the effect of PAN on the food uptake of test nymphs was dose-dependent. The optimum release rate of PAN (3.9 ± 0.14 mg / day) significantly reduced the grouping behaviour of treated nymphs compared to the controls throughout the experiment. It also reduced the food uptake and the total haemocyte count of treated nymphs compared to the controls. Of the haemocyte groups, the coagulocytes were the most affected by PAN. The NPB affected the haemocyte population of three and 15 day-old adults and gravid females. The NPB significantly increased the total haemocyte count (THC) of treated, three day-old adults and gravid females, but marginally decreased the THC of 15 days-old locusts. The increase of the numbers of plasmatocytes in the haemolymph of NPB-treated insects compared to the controls was significant in both three day-old adults and gravid females. Gregarious female locusts treated with NPB significantly dispersed their egg pods (75%) similar to the solitarious insects (81.25%). Only 25 and 37.5 % of the controls and carrier-treated females, respectively, dispersed their egg-pods. PAN enhanced mortality caused by sub-lethal doses of fenitrothion (1.19 x 10-2, and 1.79 x 10-2 mg a.i / nymph), and the lowest recommended dose of the pesticide (2.38 x 10-2 mg a.i / nymph) in third and fifth instar nymphs. This was significant on fifth instar nymphs for all three doses of fenitrothion applied three and five days after the start of PAN treatment. Similar mortality rates on fifth instar nymphs were obtained with 75% and 100% of the recommended dose of fenitrothion, when both doses of the pesticide were combined with the higher dose of PAN (3.9 ± 0.14 mg / day). Also, the results showed that at 75% of recommended dose of fenitrothion the two releases rate of PAN (3.9 ± 0.14 and 0.93 ± 0.06 mg / day) enhanced the mortality caused by fenitrothion to similar levels (66.16 and 66.19%, respectively). The best combination of both products was the application of 75% of recommended dose of fenitrothion three days after start of exposure to the lowest dose of PAN on to the nymphs. PAN also enhanced the efficacy of fenitrothion on third instar nymphs, but to a lesser extent than on fifth instar. In fifth instar nymphs, the combination of PAN and fenitrothion killed up to 4.34 times nymphs more than fenitrothion alone. This ratio was less by 1.2 times in third instar nymphs. The youngest three-day-old nymphs were significantly more susceptible to fenitrothion alone than the six or eight day-old nymphs in both third and fifth instar nymphs. PAN enhanced the mortality rate and induced growth disruptive effects characterized by delay of the moult and malformation of fledgelings. The overall mortality in all experiments was less than 50%. The malformations affected mostly the wings, hind legs, and the antennae, affecting either one, two or three organs or all three in different insects. The best combination in this study with regard to all parameters monitored (mortality and mal-growth) is that of PAN and the medium and sub-lethal dose of neem oil (39.72 x 10-5 mg a.i / nymph) applied on the same day.
Neem seed for the management of the banana weevil, cosmopolotes sordidus germar (coleoptera: curculionidae)and banana parasitic nematode complex
(2012-04-04) Musabyimana, Thaddée
The study was conducted in Western Kenya, a prime banana growing area during the period of May 1996 to February 1999. The objectives were to control the banana weevil and parasitic nematodes with neem materials, thereby reducing yield losses and contributing to sustainable banana production. The repellent, antifeedant, ovipositional deterrent, and growth inhibitory effects of powdered neem seed (NSP), Kernel (NKP), cake (NC) and neem oil (NO) on Cosmopolites sordidus and its population build-up were studied in the laboratory and outdoors tests at ICIPE's Mbita point field station (MPFS). In choice tests, 48h after release, less than 30% of weevils settled under neem-treated banana corms while more than 75% settled under untreated corms. In a feeding test, weevil larvae did not feed or fed little on neem-treated corms. Larvae caused little damage to neem-treated corms, but untreated corms were heavily damaged, indicating a strong repellent and antifeedant effect of neem seed derivatives on C. sordidus. Compared with the untreated control, 3-10 times fewer eggs were laid by female in neem-treated corms. Egg hatchability was less than 25% in neem- treated corms and more than 50% in the control. Neem treatments also inhibited larval growth and development. Forty to 60% of 2nd-instar larvae died in 14 day when confined to neem-treated banana pseudostems, the survivors were small in body size and weighed 4 to 6 times less than those in the control where less than 20% larvae died and adults were recovered. The higher the concentration of neem materials, the higher was the severity of effects. Efficacy of neem materials against the banana weevil and parasitic nematodes was evaluated under controlled pest infestation levels at MPFS. Effective rates, methods and frequency of application of the selected neem materials were determined at MPFS and in Farmers' fields, under different levels of soil fertility and pests infestation. In a pot experiment, four weeks after planting, NSP, NKP, or NC was applied at 5g per plants inoculated with 500 nematodes and 5 pairs (females and Males) of the banana weevil. Compared with control, 1.5 months after the treatment, neem materials application significantly reduced the nematode population and weevil damage on a par with Furadan applied at 5 g/plant. Similar results were obtained with the application of neem materials to pared or unpared banana suckers planted in 100 or 200l drum's capacity and inoculated with 2000 nematodes and 5 pairs (female and males) of the banana weevil per drum. NSP-or NC- treated unpared suckers supported much fewer nematodes than the pared treated suckers with same neem products, obviating the need for paring of suckers. NKP and NO applications were toxic to the banana plant and were excluded from further testing. Soil application of powered NSP or NC against the banana pests was more effective than their application in aqueous forms. Application of NSP or NC at planting time and then at 1, 2, 3, or 4- month intervals to plants grown under controlled pest infestations in drums significantly reduced nematode density and the weevil damage. Similarly, in farmers' fields, soil application of NSP or NC at 60, 80 or 100 g/mat at planting and then at 4 month-interval significantly reduced the weevil and nematode damage. Although the application of NSP or NC at 200 to 400 g/mat at 6 month-intervals significantly reduced the nematode population and weevil damage, they were toxic to the banana plant. Application of NSP or NC at 60, 80 or 100 g/mat at 4-month intervals to a fertile soil with a moderate pest load, increased yields by 27-50% over the control during the 1st crop and by 30-60% during the 2nd crop. Furadan increased the fruit yield by 27% over the control in the 1st crop but dropped down to -2% in the 2nd crop. Under low soil fertility and high pest infestation levels, the neem treatments also controlled the pests and markedly increased the yield 7 to 10 times more than that in the control during the first crop. During the second crop, all plants in the control plots dried up before fruiting, but neem-treated plants continued to produce bunches. Depending on the soil fertility and doses of application, net gain over the control obtained with the application of NSP or NC ranged from US $ 70 and US $ 800 per hectare. However, a loss of US $ 700/ha was observed with the Furadan application. Neem application of doses higher than 100 g/mat was also uneconomical. The beneficial effects of neem seed materials application on the banana plant growth, pest control, and implications of these findings in the banana pest management and further areas of investigation are discussed.
Cultural management of banana weevil cosmopolites sordidus germar (coleoptera: curculionidae) for improved banana field in Western Kenya
(2012-04-04) Ngode, Lucas
Studies on the effects of planting materials, weevil trapping, and intercropping on the banana weevil cosmopolites sordidus Germar. and crop yields were conducted in western Kenya from 1994 to 1997. The objectives of the investigations were to explore the efficacy of non-pesticidal options for the management of the banana weevil. Field experiments were undertaken using clean planting materials, pseudostum traps for the weevil management and intercropping banana with groundnuts Arachis hypogaea L. different banana plant densities. Results indicate that paring and hot water treatment is effective in cleaning infested banana planting material. It did not affect the banana growth and yield performance. The infested planting material resulted into significantly high weevil damage and yield losses within two crop cycles compared to the infested but pared and hot water treated material. The lowest damage of 12.6% was recorded under furadan protection while the highest damage of 66% was in the infested suckers. The infested, pared and hot water treated material suffered 17.6% damage while in the healthy material it was 16.3% during the three crop cycles. The banana bunch yield under insecticide protection was 14.5 kg and in the healthy plant it was 15.3 kg whereas the infested, pared and hot water treated material yielded 13.3 kg. These weights were not significantly different from each other but differed significantly different from each other but differed significantly from the infested materials yield of 6.8 kg. The associated yield losses were 53.1% in the infested materials, 16.6% under paring and hot water treatment and 8.3% under insecticide protection. The use of split pseudostem traps for weevil management at low weevil population density significantly reduces the number of adult weevils and larval damage caused. However, trapping where the infestation and resulting damage is already high may not result into significant population decrease and yield responses. Intercropping banana with groundnut did not affect weevil colonizing the banana but influenced their distribution during the early stage of the banana establishment. The banana crop planted at 3x3m and 5x5m spacing did not affect the growth of the groundnut during the first one year. Thereafter, the banana canopy significantly reduced the growth and yield of the groundnuts in the 3x3x banana spacing. Nevertheless, spacing significantly influenced the banana yield per unit area with the 3x3m banana spacing yielding more than double that of the 5x5m spacing. The number of flower thrips and aphids were reduced in the banana intercrop compared to those in the groundnut monocrop. Incorporation of organic mature improves the banana performance. Nevertheless, with increased bunch weight snapping of the banana became significant due to the weakened corms. Thus, the use of clean planting materials, weevil trapping and application of organic manure are essential components of banana weevil integrated management.
Interaction between arbuscular mycorrhiza fungi (AMF) and meloidogyne hapla on pyrethrun in Kenya
(2012-04-05) Wanjohi, Waceke J.
In this study, mycorrhizal status of pyrethrum in Kenya was determined. Fungal isolates obtained from pyrethrum fields were screened for efficacy against M. hapla and in improving pyrethrum growth. Effect of inorganic P fertilizers and intercropping on Glomus sp. (isolate KS14), one of the effective isolate against M. halpa was dertermined. To determined mycorrhizal status of pyrethrum, spores were extracted from soil samples obtained from 30 different study sites and their abundance (numbers) and composition (types) determined. In addition, percent growing ecozones; Kisii, Limuru study and Molo representing low, mid and high altitude ecozones, respectively. In general, Limuru study sites revealed lower percentage of root colonization, higher spore were characterized and placed into various AMF genera. Except for Sclerocytis spp. five of the six known AMF genera were encountered in the study sites. Glomus was the most commonly encountered genus (10 isolates) followed by Acaulospora (5 isolates). Only one isolate of Entrophospora was present. In the screening tests, arbuscular mycorrhiza fungal (AMF) isolates; KS14 (Glomus sp.3); KS 18 (Glomus etunicatum), KS74 (Scutellospora sp.3), ML34 (Glomus sp.6), ML35 (Glomus sp.7, LM61(Glomus sp.4) and LM83 (Gigaspora sp.3) were screened . Fungal mixed inoculum (20g) was incorporated into sterized sand-soil mixture before planting with 6-week-old pyrethrum seedlings. The inoculum consisted of spores, hypla, infected root fragments and soils in which the plants for inoculum production were growing. The plants were inoculation with 6000 M. hapla second stage juvenile (J-2) 3 months after fungal inoculation. Dry shoot weights, fresh root weights, percent root colonization by the fungi, nematode gall indices, number of eggs, females and J-2 were determined at the end of the experiment 2 months after nematode inoculation. Root length was also determined where possible. Isolates KS14, LM61, KS18 and KS74 significantly improved top biomasses of fungus-treated and fungus-nematode-treated plants. Isolate KS14 was the most effective (47% top biomass increase) followed by isolates LM61 and KS18 (33%). Isolates ML34, ML35 and LM83 improved top biomasses of fungus-nematode-treated plants. Fungal isolates KS74 and ML34 significantly increased fresh root weights of pyrethrum by 45% and 50%, respectively. Isolate KS18 reduced pyrethrum by 45% and 50%, respectively. Isolate KS18 reduced pyrethrum root length by 18%. Except fungal isolates ML34 and ML35, all the other isolates suppressed M. hapla disease severity and egg production. Isolate LM61 (86%) was the most effective followed by KS14 (75%). Isolates KS18, KS74 and LM83 suppressed disease severity and egg production by up to 75%, 32% and 37%, respectively. All the fungal isolates screened significantly reduced the number of females in the root system and J-2 in the soil. The presence of nematodes in fungus-treated plants did not affect root colonization by the fungus except in KS18, ML34 and ML 35-treated plants. In testing for effects of inorganic P fertilizers on efficacy of KS14, Triple super phosphate (TSP) and Single super phosphate (SSP) were used. The fertilizers were applied at two rates (1 and 2g/g soil) at the time of fungus inoculation. Two months after, plants were inoculated with the nematodes. The plant growth and nematode disease parameters were determined at the end of the experiment, 2 months after nematode inoculation. The fertilizers at both levels improved plant growth of non-mycorrhized, mycorrhized, non-mycorrhized-nematode and of mycorrhized-nematode-treated plants. The fungus in general improved plant growth on its own or in the presence of nematodes but not in the presence of fertilizers. The fungus, however, improved plant growth by a lesser percentage than both fertilizers at both levels. The fungus unlike the fertilizers, suppressed nematode's disease severity. The suppressive effects of the fungus were, in most cases reduced by the fertilizers. In addition, the fertilizers significantly reduced root colonization of pyrethrum by the fungus. The nematodes, on the other hand, did not have any significant effects on root colonization by the fungus or on its ability to improve pyrethrum growth. The presence of nematodes in fertilizer or fertilizer-fungus-treated plants, however, significantly reduced pyrethrum growth. Efficacy of isolate KS14 to improve pyrethrum growth was tested in presence of maize and/or bean intercrops. Pyrethrum plants inoculated with 20g of KS14 and left to grow for 3 months were intercropped with maize and/or beans. Two months after planting the intercrops, pyrethrum dry shoot and fresh root weights were determined. Percent root colonization on the three crops by the fungus was also determined. In general, maize significantly reduced shoot and root weights of mycorrhized and non-mycorrhized plants. In addition, maize significantly reduced root colonization of pyrethrum. Beans on the other hand, significantly reduced shoot and root growth of mycorrhized plants but not of non-mycorrhized plants. Beans did not have any significant effects on root colonization of pyrethrum by the fungus. A combination of both intercrops had no significant effects on shoot weights of mycorrhized pyrethrum but reduced that of non-mycorrhized pyrethrum. Pyrethrum root colonization by the fungus was not affected by the presence of the two intercrops. Both maize and beans are hosts of the fungus.
The influence of drip irrigation on ecophysiology and yield of arabica coffee hybrid Ruiru 11
(2012-04-11) Gathaara, M. P. H.
The influence of drip irrigation on Coffee arabica L. cultivar Ruiru 11 was studied in a field experiment. Drip irrigation was applied when a soil moisture deficit (SMD) of 100 mm was recorded. FOur drip irrigation rates (25, 50, 75 and 100 mm of water) were applied to offset the SMD by 25%, 75% and 100%. These were applied at intervals of 21, 28 and 42 days. The control treatment was unirrigated. Primary (first order) branch extension growth, stomatal conductance, CO2 assimilation, leaf water potential, biomass accumulation, root distribution, yield and quality were measured. The drip irrigated coffee plants had a significantly higher primary branch extension growth rate (8.1 mm wk-1), stomatal conductance (0.605 mol m-2 s-1) and leaf water potential at 14.00 h (-1.98 MPa) than the unirrigated plants. The corresponding growth rate, stomatal conductance and leaf water potential in the unirrigated plants were 1.2 mm wk-1, 0.368-mol m-2 s-1 and -2.67 MPa. Irrigated plants had higher CO2 assimilation rates in the upper levels of the plant canopy when compared to the unirrigated ones. Root distribution was not significantly influenced by irrigation. However the mean vertical distribution (125 cm) was about half the horizontal distribution (232 cm). The unirrigated coffee had a total coffee yield of 6142 kg per ha. The 25 mm, 50 mm, 75 mm and 100 mm irrigation rates resulted in yields of 9373 kg, 10531 kg, 10307 kg and 8726 kg per ha respectively. Theses represented increases of 52.6, 71.5, 67.8 and 42.1% respectively. The results showed that the 50 mm irrigation rate may be optimal. Evidence that dry season water requirements for the cultivar may be met by low irrigation rates at short intervals is presented. The practical implications of the results are discussed.
Phytoplankton and nutrient dynamics at Turkwel Gorge Reservoir, a new man-made lake in northern Kenya
(2012-04-17) Kotut, Kiplagat
Spatio-temporal variation in some physicochemical and phytoplankton parameters were investigated at Turkwel Gorge Reservoir and its inflowing and outflowing rivers between 1994 and 1995. Seasonal variation in inflow volume had the most impact on the reservoir conditions investigated. A wide difference between wet and dry season inflow volume had the most impact on the reservoir conditions investigated. A wide difference between wet and dry season inflow volume combined with a regulated outflow independent of season resulted in a drawdown of over 10m in each year. Reservoir Secchi depth ranged from 0.09m (wet season) to 2.80 m (dry season). Low levels resulted from turbid flood inflows. Electrical conductivity (EC, S cm-1) varied from 140-200 (reservoir), 107-210 (inflowing river) and 155-200 (outflowing river). Total alkalinity (TA, as mg1-1 CaCO3) ranged from 80-111 (reservoir), 62-125 (inflowing river) and 80-113 (outflowing river). Low levels of EC and TA were observed during the wet season. A functional relation between EC and TA (TA = 0.529 EC: R2 = 0.876) was established suggesting a predominance of carbonates among the anions. Variations in pH were from 6.7-8.9 (reservoir), 1.8 - 8.2 (inflowing river) and 0.4 - 6.4 (outflowing river). High pH and DO levels at the reservoir were observed during the wet season and were the result of higher phytoplankton photosynthesis. Floodwater inflow and hypolimnetic oxygen depletion possibly brought about low levels of pH and DO at the beginning of the wet season in the inflowing and outflowing river sections respectively. Detectable levels of nitrite nitrogen (NO2-N) were noted at all study sites during the wet season. Nitrate nitrogen (NO3-N, g1-1) varied from 6.7-111.1 (reservoir), 53.3-482.2 (inflowing river) and 8.9-111.1 (outflowing river). Total nitrogen (TN, g1-1) ranged from 119-526 (reservoir), 205-3354 (inflowing river) and 82-624 (outflowing river). Phosphate phosphorus was mostly undertectable. Total phosphorus (TP, g1-1 ranged from 8.9 -71.6 (reservoir), 101.8-1259.4 (inflowing river) and 8.6-31.3 (outflowing river). Variation in NO3-N was mostly irregular except for a wet season increase at the inflowing river. In general, TN and TP showed a wet season increase explicable by an increase at the inflowing river loading. Dissolved reactive silica (DRS, mg1-1) varied from 0.41 to 9.77 (reservoir), 9.01-19.93 (inflowing river) and 5.07-9.77 (inflowing river). Reservoir DRS showed a wet season decline that had an inverse correlation to total diatom biomass (P=0.001, n=12). Estimates of input and output balance of NO3-N, TN, PO4-P, TP and DRS in 1994 revealed a reservoir areal loading rates of 5.98, o.75, 10.90 and 408.5 mg m-2 with a reservoir retention of 78, 74, 94, 95, and 46 percent respectively. Reservoir chlorophyll a (g1-1) ranged from 4.8 to 36.9 (1994) and 4.9 to 11.4 (1995) with coefficients of variation of 42% and 8% respectively. Greater variation in 1994 resulted from higher inflow volume. Outflowing river chlorophyll a ranged from 1.07 to 8.31 g 1-1 with low levels resulting from reduced DO concentration. Positive correlation between mean reservoir chlorophyll a (n=13) and inflow volume (P=0.007), NO3-N (P=0.04), TN (P<0.001), and TP (P<0.001) was observed in 1994. A positive correlation with inflow volume (P=0.005) and TN (P<0.001) was observed in 1995. Phytoplankton diversity (bits based on natural log) at the reservoir varied from 0.18 to 2.43 bits with an inverse correlation to total counts (P<001). Total counts ranged from 2.52 - 77.60 (1994) and 4.57-23.90 (1995) million units 1-1. Species density change varied from a distinct seasonality, through a wax and wane character to a nearly uniform density throughout the annual cycle. Throughout the study period, Achnanthes exhibited a distinct seasonality, characterized by a very high cell count during the wet season and very low counts during the dry season. However, the reservoir peak density in 1994 (75.6x106 cells 1-1) was much higher than in 1995 (3.7x106 cells 1-1). The majority of the other species exhibited a wax and wane pattern with greater amplitude in 1994. Dominance in unit counts varied throughout the study period. In 1994, while the dry season was characterized by a quick succession in dominance, Achnanthes dominated the wet season. Coccoid Cyanophyceae dominated most of 1995. Phytoplankton density changes at the outflowing river followed a pattern close to that of the reservoir with lower unit counts. Total phytoplankton biomass (mg1-1) at the reservoir ranged from 0.44-11.17 (1994) and .49-1.35 (1995). Positive correlation between phytoplankton biomass and the loading rates of NO3-N (P=0.009), TN (P=0.040), TP (P=0.011) and DRS (P=0.033) was established in 1994 suggesting the reliance of biomass increase on inflow nutrient recharge. Among the phytoplankton divisions represented, only the Bacillariophyceae showed a regular wet season peak biomass that can be explained by their dependence on the nutrient rich turbulent inflows of this season. Variation in the other divisions was less regular with peak biomass levels at different times of the intervening period. The Bacillariophyceae contributed biomass in both 1994 (88%) and 1995 (40%). Outflowing river phytoplankton biomass changes (range, 0.27-6.72 mg1-1) showed a positive correlation to reservoir phytoplankton biomass (P<0.001) suggesting that the reservoir is the source of downstream flora. Reservoir primary production ranged from 1.85-9.67 (1994) and 3.00-5.41 (1995) g O2m-2 day-1. High rates were characteristic of the wet season while low rates occurred during the dry season especially following an overturn. High inflow volumes therefore transform the reservoir that is on average mesotrophic to a hypereutrophic state while low inflow volumes or mixing reduce the reservoir that is on average mesotrophic to a hypereutrophic state while low inflow volumes or mixing reduce the reservoir to an oligotrophic state.
A study of the determinants of diversity and biosystematics of agromyzidae associated with leguminosae
(2012-05-25) Tengecho, C. B.
Leafmining Agromyzidae has been reported to cause damage a wide variety of crops. Spencer (1973) Compiled a comprehensive review of the damage caused by the family and listed 156 pest species. He also provided summarized information on the morphological identification, biology, distibution and control of agromyzid pest species. This study is concerned with the identification of eleven agromyzid species that could be collected easily from legumes in Kenya. Although Kenya has approximately 602 species of leguminous plants only a total of 14 agromyzid species were reported to be associated with them. These were 3 species in the genera Tropicomyia, 3 in Ophiomyia, 2 in Liriomyza, 1 in Chromatomyia and 5 in elanagromyza. First and foremost major determinants of diversity of Agromyzidae associated with leguminous plants were analysed using multiple regression.The theory that geographically ubiquitous species of plants have more species of insects feeding on them than similar but less widespread species was shown to hold true for the Kenya leguminous plants so area alone can explain most species richness in any region. Similarly the logarithmic plot of species-area relationship indicated that variations not accounted for was possibly due to the leaf-form, different number of habitats, altitude and taxonomic isolation. The drawback was inadequate botanical collecting of leguminous plants in Kenya, which possibly limited the species-area effects to only 16%. Gel electrophoresis was also used to score enzyme mobilities of ten different species first using polyacrylamide gel then isoelectic points of the different proteins examined. All were diagnostic in separating the ten species of Agromyzidae.Starch gel electrophoresis was also carried out and an account of the species variation was provided, based on the data obtained. It can be suggested that enzymic data should be used as taxonomic characters in parallel with morphological, anatomical and multivariate characters. However from using the enzyme profile of mostly wild individuals all the ten species studied could be placed into distinctly separate genera. Out of four genera occurring in Kenya that were revised the species O. spencerella, O. phaseoli, M. chalcosoma, M. vignalism. T. flacourtiae, Melanagromyza spp. and C. horticila were found to be distinct. However overlap or relatedness existed between them the enzymes that distinctly separated these species were non-specific esterase enzyme, Malic dehydrogenase, Malic enzyme, Glucose-6-phosphate dehydrogenase, Hexokinase and phospho gluvose isomerase. An attempt was also made to see whether the populations from different host plants could be separated statistically bymeasurements calculated for both male and female using wilk's Lambada stepwise discriminant method, The measurements taken were ten morphological characters of Chromatomyia horticola,sixteen Morphological characters of Ophiomyia spencerella populations collected from different localities in Burundi and one locality in Kenya, sixteen morphological characters for O. phaseoli from Sri Lanka and Kenya and seventeen morphological characters for seven species associated with legumes. The proportion of the proximal to the distal part of the wing vein M3+4 was shown to be the best character that separated the five populations of C. horticola into two clusters. The first cluster consisted of Galinsoga parviflora, Bidens pilosa and Sonchus oleraceus while the second cluster consisted of Solanum spp. and Solanum nigrum. Moreover the other nine characters were similar for the five populations studied. This suggests the possible variation for populations of of agromyzid species on different host plants. the populations of O. spencerella from different areas in Burundi and one locality in Kenya were shown to be easily separated by seven different characers shoeing differences in the populations from the different areas. All the seven species of Agromyzidae associated with legumes showed distinctness but overlap existed in male O. spencerella, O. phaseoli and C. horticola. Similarly overlap existed in female O. phaseoli, T. vigneae, L. trifolii and C. horticola. Using genitalia preparation, multivariate analysis and gel electrophoresis, it was shown that the species of agromyzidae on legumes were no coherent and diverse. This confirms their placement into different genera in most existing keys.
Fungal parasitism of root-knot nematode eggs and effects of organic matter, selected agrochemicals and intercropping on the biological control of meloidogyne javanica on tomato
(2012-06-05) Owino, P. O.
Root-knot nematodes are serious pests all over the world. Over 50% Pyrethrum losses have been associated with these pests in Kenya. Chemical management of these organisms is effective but difficult to sustain for long-term benefits, and alternative control measures must be sought. The use of fungal antagonists may provide an alternative but factors affecting their efficacy are not known. Therefore, in vitro, in vivo and greenhouse tests were conducted at Kenyatta University, Nairobi, Kenya, to compare efficacy of the fungi Paecilomyces lilacinus Thom(sam), Fusarium oxysporum Schlecht isolates 1, 2 and 3, and Phoma herbarum against root-knot nematode eggs, egg masses and females, and (2) assess whether aldicarb (10% Temik), captafol (orthodifolatan 80% wp), organic matter and intercropping with the nematicidal plants Tagetes minuta L, Datura stramonium L,. and Ricinus commnis L., could stimulate , inhibit or have no effect on the biocontrol potential of P. lilacinus, tomato (Lycopersicon esculentum (Mill) shoot heights and weights, nematode population in soil, gall index and number of galls per gram root weight were assessed using standard methods. Gall index was based on a subjective scale of 0-4, where 0=no gall and 4=76 - 100% of the root system galled. To obtain the P. lilacinus isolate and other fungi for this study, 120 fungal isolates were isolated from nematode eggs extracted from soils collected from fields in Kakamega, Kiambu, Nyeri, Mombasa, Baringo, Kisumu, and Kisii districts. Isolates that parasitized 30-95% of eggs on agar were selected for further tests. Paecilomyces lilacinus and F. oxysporum isolate 1 parasitized significantly (P<0.05) more M. javanica eggs and females on agar than F. oxysporum isolates 2 and 3, and P. herbarum,. P. lilacinus F. oxysporum isolates 1,2 and 3, and P. herbarum parasitized up to 91.9% eggs and 87.3% females, 82.4% eggs and 79.1% females, 25.9% eggs and 44.7% females 9.4% eggs and 19.2% females and 29.5% eggs and 60.6% females, respectively, on water agar. Levels of egg parasitism, however, were lower in sterile field soil. P. lilacinus and F. oxysporum isolate 1, the most aggressive isolates on agar, parasitized only 22.2% and 19.6% of the eggs in sterile soil, respectively. Besides egg parasitism, the five fungi influenced egg hatch differently. Up to 22.2%, 24%, 24.1%, 55.8%, and 74.4% of egg hatched on WA plates inoculated with F. oxysporum isolate 1, P. lilacinus, P. herbarum, F. oxysporum isolate 2, and F. oxysporum isolate 3, respectively. Chicken manure, and the nematicidal plants T. minuta, D. stramonium and R. communis significantly increased egg parasitism by up to 112, 72, 54.9 and 106.3% respectively, when compared to controls. The nematicidal plants also stimulated parasitism of M. javanica eggs were parasitized in soils planted with R communis T. minuta and D. stramonium, respectively 50 days after inoculation, compared to 23.2% in controls. Levels of egg parasitism were however, lower, 17.6, 16.4 and 15.1% respectively, 98 days after inoculation compared to 10.3% in controls. In both cases, percentages of egg parasitism were higher than those obtained in non-amended soils, but lower than those obtained on water agar. R. communis, T. minuta and D. stramonium increased egg parasitism by 3.2, 28.4 and 22% respectively, 50 days after noculation. The treatments, chicken manure, R. communis, D. stramonium and T. minuta also suppressed nematode population and gall development significantly than controls. Galling indices were decreased by up to 76.5%, 35.3, 47% where chicken manure, R. communis, D. stramonium and T. minuta were used, respectively. These treatments enhanced shoot weights by up to 159, 106, 100, and 64.7% respectively when used in combination with P. lilacinus. Delaying the time of planting tomato in soil amended with chicken manure and infested with P. lilacinus from 0 to 8 weeks increased egg parasitism significantly (b=1.9;) and significantly reduced gall development (b=-0.5; r=-0.9). Tomatoes planted in chicken manure-amended soil 8 weeks after incorporation of chicken manure and P. lilacinus were significantly heavier than those planted 0 - 6 weeks after soil amendment. The number of juveniles increased with time of planting in soil not amended with chicken manure (b=+2.1; r=0.44) but the increase was not significant. Significant decrease in galling index with time of planting (r=-0.95) was observed in pots treated chicken manure alone or in combination with P. lilacinus. In general, aldicarb and chicken manure were effective in suppressing gall development and nematode population build up, whether used alone or in combination with P. lilacinus. Among the nematicidal plants, R. communis enhanced egg parasitism more significantly than T. minuta or D. stramonium. However, the maximum levels of egg parasitism achieved in all tests were less than 40%, an indication that the treatments used may not enhance egg parasitism to levels that can reduce nematode populations significantly in the field.
Nitrogen fixation in faidherbia albida (chev) Del
(2012-06-07) Gitonga, Nkanata Mburugu
Nodulation and arbuscular mycorrhizal infection was assessed in soils obtained from two habitats of Faidherbia albida in different ecoclimatic zones. A third site in a semi arid area but without F. albida was also assessed. All three sites had Bradyrhizobium spp, Rhizobium spp and arbuscular mycorrhizas. Soils from the two sites with F. albida differed in soil mineral content, nodulation and mycorrhizal infection of F. albida and Acacia senegal. In laboratory experiments it was observed that F. albida took about 21 days to nodulate. Inoculated seedlings suffered an early period of nitrogen stress. Application of combined nitrogen alleviated early nitrogen stress but reduced nodulation and nitrogen fixation. Combined nitrogen in form of NG4+ had less severe effects on nodulation than NO3- at the three levels of N (0.5, 2.5 and 5.0 mol m-3) tested. In an experiment using 5.0 mol m-3 N provided as 15NO3- (5 atom %) or as 15NH4+ (5 atom %) it was established that preference for nitrogen form was pH dependent. Nitrate was preferred at low pH (5.5) and ammonium at high pH (6.5). The N form/pH combination resulting in good plant growth had also less severe effects on nodulation and nitrogen fixation. Improvised glass fronted gutter containers, made from open gutter pipes were used for monitoring taproot elongation. Effect of N2, NO3-, and NH4+ at mol m-3 was assessed. The taproots elongated very quickly but independently of nitrogen for at least the first 70 days. There were also no statistical differences between taproot elongations in three provenances of F. albida tested. In an experiment to find out the effects of phosphorus and nitrogen form of F. albida, phosphorus was found to increase nodulation and nitrogen fixation. High levels (above 3.0 mol m-3) of phosphorus reduced plant growth, nodulation and nitrogen fixation. A statistically significant interaction was observed between nitrogen form and phosphorus levels. The contribution of arbuscular mycorrhizas to growth, nodulation and nutrient uptake in F. albida seedlings at 0.2, 0.5 and 1.0 mol m-3 was not statistically significant. There were no statistically significant differences between F. albida seedlings grown at 0.5, 50.0 and 75.0 mol m-3 NaCl. Percent nitrogen and nitrogen content were statistically lower in plants grown at 75.0 mol m-3. However the ratio of carbon to nitrogen was significantly higher in plants grown at 75.0 mol m-3 compared to 0.5 and 50.0 mol m-3 NaCl. It has been shown in this study that nodulation, nitrogen fixation and growth of F. albida is influenced by nitrogen form and levels, phosphorus levels, pH and salinity. It is also evident from the results that agronomic protocils can be designed to militate against conditions adverse to growth and nitrogen fixation of the tree. It is envisaged that change of agronomic practices in the growth of F. albida coupled with selection of both macro and micro-symbiont for the field conditions will improve growth and nitrogen fixation of the tree.
Distribution, Behavioural Biology, Rearing and Pollination Efficiency of Five Stingless Bee Species (Apidae: Meliponinae) in Kakamega Forest, Kenya.
(2013-08-01) Kiatoko, Nkoba
The study on distribution, behavioral biology, rearing and pollination efficiency of five stingless bee species (Apidae: Meliponinae) in Kakamega forest, Kenya showed that; species diversity was higher at Ivihiga compared to Isiekuti sites. Within habitats, species diversity varied and the indigenous and the mixed indigenous forests had more species diversity than the other habitats. The number of nesting habitats and also the chance of getting a nest of a particular species within nesting habitats varied among the stingless bee species. The nest pattern was under-dispersed for almost all the species nesting in the indigenous forest; mixed indigenous forest and grassland with the indigenous tree species. The nesting pattern for M. ferruginea (reddish brown) and H. gribodoi changed from an under-dispersed and over-dispersed pattern, respectively, to a clumped nest pattern when nesting in the homesteads. Within interspecific species nesting in the same habitat and within the nesting habitats of conspecific species; a difference was observed in the average nearest neighbour distance separating their nest entrances. Three different nesting sites were identified overall species (tree, underground, residential houses). Nest aggregation was observed within four bee species (except M. lendliana) and the average less minimum nearest neighbour distance between nests aggregated on a single substrate varied within conspecific and interspecific aggregation. Daily temperature and humidity influenced the bee flight activities out for foraging or grooming; with temperatures below 22oC and relative humidity above 70% being not ideal for the five bee species to start or maintain their out going flight activity. M. ferruginea (reddish brown) and H. gribodoi were the only species which bite to defend their nests from intruders. M. ferruginea (reddish brown) and M. lendliana were the only species which completely seal the open entrance of their nests at night. Acceptance of the designed hive types varied across bee species. All types of hives designed for M. ferruginea (reddish brown) were accepted at a probability of 0.63 and above. M. ferruginea (black) showed preferences for the two non compartmented hive designs and OATH hive type at a probability of 0,63 and above. H. gribodoi accepted only the icipe 1 hive model compared to the two designs of compartmented hives. M. lendliana preferred nesting only in the hives made out of clay as opposed to wooden hives. Three colonies of M. bocandei were succefully reared in the icipe 1M hive design. The average annual honey production under domestication varied among the five bee species and was higher in the M. bocandei species (3.13 ± 0.21 litres). The hive splitting method was more successful in propagation of colonies of three Meliponula species. Natural enemies recorded in this study included mainly parasites, predators and disturbers. Lastly, flowers of green pepper pollinated by H. gribodoi produced heavier fruits with superior number of seeds and the seeds were bigger compared to those produced by self-pollinated flowers or flowers pollinated by feral insects.
Efficacy of Selected Medicinal Plants Used by the Ogiek Communities against Microbial related Infections
(2014-02-24) Amuka, Omari; Okemo, P. O.; Mbugua, P. K.
Ethnobotany and traditional medicines have been used for bioprospection for modern pharmaceutical in all the world continents. In Kenya the ethnobotanical of several communities has revealed that plants are important source of medicinal products that require further research to establish their validity, efficacy and quality of health services. The Ogiek communities who currently live in harmony with nature and have minimal with modern cultural practices exhibit high potentials for discovery of new pharmaceutical products through ethnobotanical, phytochemical, and microbial strategic studies. Furthermore, such studies have been necessited by newly emerging and reemerging diseases and the development of resistance of diseases to the drugs that are currently in use. The Ogiek community, who has lived in Mau forest for over six centuries, is fast being assimilated into other culturally stronger communities. However, their life is shrouded in secrecy and their rich cultural practices including ethnomedicine are being lost. Ethnobotanical field surveys revealed that over 80% of the Ogiek community has constructive knowledge of the forests and forest products. They have clear knowledge of medicine plants, their pharmaceutical procedures and pharmacological manifestations. It was evident that majority of the human health complaints were parasitic, bacterial, and fungal in nature. Symptomatic areas were the abdomen, chest, and the head. A total of 49 plant species in 33 families were collected. Bioassay of the extracts showed that some of the plant species possessed promising antimicrobial activities. In order to verify the efficacy of the drugs, selected pathogens were selected and in vitro studies carried out on individual crude extracts and essential oils. It emerged that 16 plant species showed reasonable biological activities on the selected human pathogens. Further studies to confirm the efficacies of the drugs were successfully done to establish the susceptibility (MIC, MBC and MFC) individually. Several metabolites known for their efficacy were identified. There is need to further document the Ogiek culture, in situ and ex-situ conservation of the Mau forest complex so as to conserve the biodiversity for the future generations. Further elucidation of the extracts may lead to discovery of new pharmaceutical compounds that could be used in the synthesis of new drugs for the currently challenging medical conditions.

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