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    Screening Selected Common Bean Genotypes for Resistance to Xanthomonas Axonopodis Pv. Phaseoli Constraining Bean Production in Kakamega County, Kenya
    (Kenyatta University, 2020-07) Chepkemboi, Angeline
    Beans play a significant role in food security owing to its nutritional value and generation of income. However, output of beans in Western Kenya is hindered by diseases, pests, soil infertility and unfavorable weather resulting to low productivity. Of the many diseases of beans, common bacterial blight (CBB) caused by Xanthomonas axonopodis pv. phaseoli (Xap) is a disease of economic importance in common beans (Phaseolus vulgaris L.). Due to the fact that chemicals have not been effective against CBB, the use of resistant genotypes is a central management strategy. The current study was carried out in the field and in the green house of KALRO-Kakamega in 2013 and 2014 to screen nine bean genotypes for resistance to common bacterial blight disease. Experiments were conducted in randomized complete block design with three replications in a 9×2×2 factorial factor during the greenhouse and field screening and 4×2×2×2 field experiment when assessing the role of soil amendments and method of cropping on disease incidence and severity. During growth, data on plant height, number of pods/plant, length of pods and size and number of CBB spots was taken. Yield parameters were also assessed. During the study, the isolates that were recovered from leaf samples were categorized as Xanthomonas like, with regard to their yellow pigment and convex mucoid morphology. Reaction to Xap was assessed as the number of spots on the leaves and diseased leaf area (DLA). The findings from the experiment revealed a significant variation (P<0.05) on the entire traits studied among the nine bean genotypes. The experiment revealed that the mean CBB disease severity was significantly lower in bean plants that were not inoculated compared to those that were inoculated. Disease incidence, distribution and severity differed significantly (P<0.05) among the different bean genotypes. The CBB was significant (P<0.05) in the bean genotypes and was influenced by the soil amendments applied and the method of cropping used either monocropping or intercropping. Data from the field and greenhouse experiments were in conformity. None of the evaluated genotype was immune to CBB. CAL77 and Cal 156A genotypes exhibited high level of resistance to CBB, thus a better variety to use. Seven genotypes namely Cal 285, Cal 256, CAL271A, Cal274, KK 8 and Cal 87 showed moderate resistance. In the green house, it was observed that disease symptoms were severe in beans planted in non-sterile soil and inoculated with Xap compared to those planted in sterile soil and non-inoculated respectively. In the field trials, it was noted that bean plants grown with DAP were significantly (P<0.05) taller, had more number of pods per plant and significantly (P<0.05) higher yield per plot than those grown on soils with chicken manure. Monocropped beans had significantly (P<0.05) higher growth and yield parameters that were studied. This study therefore recommends that further evaluation and screening be done, susceptible genotypes be tried in other locations; establish the factors that confer high levels of tolerance in Cal 77 and Cal 156A and advice farmers on the correct farming methods.
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    Cytogenetic studies of some Kenyan tea clones (camellia Sinensis) l.o. kuntze) karyotype and ploidy.
    (Kenyatta University, 1990) Wachira, Francis Nyamu; Njagi, G.D.E.; Magambo, M.J.S.
    A comparative intraclonal analysis of ploidy states and karyotypes was performed on eight Kenyan tea clones (Camellia sinensis L.O. Kuntze), by examining shoot meristematic cells. C-metaphase chromosomes were studied by acetopropionic orcein staining methods. Several karyotypic variables VJere determined for each clone; chromosome number, short arm length (S), long arm length (L), total chromosome length (TL), arm ratio (r), relative chromosome 1ength (RL), and the presence or absence of secondary constrictions and satell ites (SAT). Clones 7/9, S15/10, 6/8, 31/8, TN14/3 amd 57/15 were all shown to be diploids w it.h chromosome complements of 2n - 2x = 30. Clones 84/2 and 84/1 we re confirmed to be naturally occurring triploids with chromosome complements of 2n=3x=45. Analysis of variances for the means of chromosomal variables, notably total chromosome lengths, indicated that there were significant (P<0.05) differences between chromosome pairs within each complement. Except for a few instances, corresponding chromosomes among the diploids were, however, shown not to differ significantly in length. In this case, therefore, chromosome lengths failed to yield diagnostic mar ke rs related to the six diploid clones and their phenotypes (yield and quality potentials). vi Corresponding chromosomes among the t.wo triploid clones wo re howave r shown to be more variable. The triploid clones similarly had their chromosomes reduced by as much as 14% in length as compared to their diploid counterparts. Arm ratios for the haploid chromosome complements within all the eight clones decreased along w ith chromosome lengths. Using arm ratios to define centromeric positions, all the eight clones were shown to have ch romosomes wh ich we re essent iall y metacentr ics. The decrease in arm ratios with chromosome length therefore meant that the shortest ch romosomes with in each comp 1ement were either perfect or near perfect metacentrics. Secondary constrictions and satellites were also shown to be consistently absent in all the eight clones. Preliminary wo rk on Giemsa staining did not give positive results and had very limited success in resolution of chromosomal structures for all the eight clones.
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    A survey of some cucurbitaceae species in Kenya with an analysis of cucurbitacin content, and an identification guide to poisonous and safe species
    (Kenyatta University, 1992) Njoroge, Grace Njeri
    The Cucurbitaceae is a family of dicotyledonous plants. For a long time the plants in this family have been cultivated as sources of vegetables and fruits. Many of the wild species are reported to be used locally as sources of vegetables. While others are given to domestic animals as fodder. Some of the wild species however. have been reported to poison people as well as domestic animals that may feed on them. Cases of poisoning could be as a result of misidentification of these species . For investigation into this problem a total of 23 cucurbitaceous species were collected from Nairobi area as well as from the surrounding areas. These plants were identified and voucher specimens deposited at EA. Cases of poisoning in cucurbitaceous species have been attributed to the occurrence of a group of triterpenoid compounds called cucurbitacins. The presence or absence of these compounds in the various organs of these cucurbitaceous species is determined firstly by test and triphenyltetrazolium chloride secondly by the infrared precipitate absorption spectrophotometer. Individual cucurbitacins were provisionally identified by thin-layer chromatography with authentic samples. Presence or absence of the toxic cucurbitacina was assessed in the various organs which are used locally as sources of vegetables or herbal medicines. It is possible from this work to distinguish the plant parts with toxic cucurbitacina and identify the plants in the field using the key presented. To make the results of this study available to the local people who use them an identification key was constructed . This key avoided technical botanical terms . which implies that it can be used by people without botanical training to identify the plants in the field. Simple illustrations are included in the key to aid identification. In addition, the local uses, distribution and flowering times of these species were investigated. It is hoped that the results of this work will reduce incidence of poisoning
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    Diversity, ecology and altitudinal distribution of corticolous lichens in Mount Kenya Tropical Montane Forest
    (2013-03-21) Kirika, Paul Muigai
    While recent studies indicate a high diversity of lichens in the tropical regions of the world equaling or even surpassing that of temperate areas, studies of lichens in these regions remain rare and Kenya is no exception. The aim of this study was to enhance our knowledge of lichen diversity in Mt. Kenya forest. Diversity, composition and altitudinal distribution of corticolous lichens was evaluated in Chogoria a wet forest type and Sirimon a dry upland forest. At every 200m elevation starting from the lower forest edge plots measuring 10 x 200m were established, these were further subdivided into 10 x 20m subplots from which two host trees were randomly selected for sampling. Ten sites were studied, six in Chogoria and four in Sirimon using stratified random sampling method. Four ladder quadrats measuring lOx 50 em were placed on the tree trunks 1.5m from the ground on the four compass directions and all lichens occurring inside these quadrats collected. In total 113 host trees of 13 species were sampled, Chogoria recorded higher diversity of host trees than Sirimon. A total of 245 taxa were recorded from 1007 specimens collected, these were classified into 73 genera and 38 families. Sixteen species were new for Africa while seventy three were first records for Kenya, seven new species were discovered. Majority of taxa in the dataset were rare, recorded only once or twice in the samples. Chogoria forest had higher species richness (150) than Sirimon (91). Rarefaction curves were used to compare species richness and abundance in the two forest areas and among study sites. Eight non parametric species estimators were used to approximate the number of species expected from each forest. Sampling effort computed revealed adequate sampling with 67% completeness. To test for differences in lichen assemblages among study sites, MRPP was used while ordination of study sites was performed using NMS. Altitude and vegetation type had a significant influence on lichen richness, abundance and occurrence. Chogoria recorded high abundance of crustose micolichens at lower elevation whereas at higher altitudes macro lichens were more abundant. Beta diversity was high for the two forest areas as well as among the study sites indicating high heterogeneity. Subtle lichen preference for the tree host species was revealed through 1SA. Overall high family, generic and species diversities were observed. Lichen identification was done using morphological and anatomical characters of lichen thalli, apothecia and ascospores in addition to chemistry. Presence of chemical substances on lichen thalli was detected by spotting reagents that give characteristic colour changes and by exposure to UV light to detect substances that fluoresce under UV light giving characteristic colours. Standardized TLC was performed in identification of specific lichen substances. To enable biomonitoring and comparative studies more lichen biodiversity research covering other montane ecosystems is recommended. Lichen metabolites and their derivatives have great potential use in pharmaceutical and agrochemical industries, more research to determine their use in medicine and crop protection is therefore stongly recommended.
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    Some genetic effects of agrochemicals on nitrogen fixing bacteria
    (2012-05-08) Budambula, Nancy
    Ambush (Cypermethrin), Delan (Dithianon) and Dithane M-45 (Nabam) are widely used agrochemicals (pesticides). Their lethal doses (LD50) are well known. The three induce C-metaphases, micronuclei, anaphase bridges, condensation and mitostasis in V. faba but information is lacking on their effects on nitrogen fixing bacteria. This study aimed at assessing the genetic effects of the three agrochemicals on nitrogen fixing bacteria. This was done by investigating the induction of forward and reverse mutations in the laboratory and field strains of Rhizobium phaseoli strain 445, 446 & CC-511, Derxia gummosa and Azotobacter chroococcum. The effect on nodulation and dry weight was also investigated with Phaseolus vulgaris. The spot and direct tests were conducted. In the spot test sterile filter discs, 6 mm in diameter, soaked in solutions of each agrochemical at concentrations 10-6 to 10-4 ppm were placed at 9 separate points on media on which separate strains had previously been plated. Control samples of discs soaked in sterile water were used. Genetic activity was assessed in terms of proportion of discs around which growth occurred out of the total number used. Toxicity was assessed by scoring zones of inhibition of growth. In the direct test, killing effect (toxic) was assessed by plating approximately 400 cells suspended in the respective agrochemical on complete medium and assessing the emergent colonies out of the total number expected. In an attempt to map the genome of R.phaseoli 445, 446 and CC-511, the bacteria were grown minimal media supplemented with amino acids eliminated one at a time. Antibiotic resistance/sensitivity was assessed by introducing discs of antibiotics to bacterial cultures inoculated on complete media. The effects of Ambush, Delan and Dithane M-45 on nodulation by P. vulgaris were investigated by applying the agrochemicals at 103 ppm (the recommended rate), 105 ppm and 101 ppm every 10 days for 56 days. Every week for four consecutive week two plants per replicate were selected and the number of nodules was scored and the dry weight was determined. No agrochemical was applied in the controls. Ambush, Delan and Dithane M-45 reduced colony emergence and inhibited growth of R. phaseoli, D.gummosa and A. chroococcum at high agrochemical concentration (104 ppm). At low concentration (10-6 to 100 ppm) the 3 agrochemicals induced selective growth of R.phaseoli around filter discs but had no observable effect on the growth of A. chroococcum and D. gummosa. Experiments with amino acids did not elucidate the nature of growth probably due to auxotrophic pre-emption. Dithane M-45 induced antibiotic resistance and/or sensitivity in R. phaseoli 445, R. phaseoli CC-511, and in A. chroococcum in the antibiotic resistance test. High concentration (105 ppm) of Ambush, Delan and Dithane M-45 significantly (P 0.05) reduced the dry weight and number of nodules of P. vulgaris especially during the sixth to eighth week of growth. Overall the results indicate that Ambush, Selan and Dithane M-45 at high concentration are toxic to nitrogen fixing bacteria. Selective growth of R. phaseoli suggests genetic activity of the three agrochemicals. Dithane M-45 at low concentration induces antibiotic resistance and/or sensitivity in R. phaseoli 445, R. phaseoli CC-511, and in A. chroococcum. There is also evidence for reduction of nodulation and dry weight of P. vulgaris by Ambush, Delan and Dithane M-45.