Browsing by Author "Ateka, E.M."

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    Additive main effects and multiplicative interaction analysis of genotype x environmental interaction among sweetpotato genotypes
    (2009-04-08) Mwololo, J.K.; Muturi, Phyllis W.; Mburu, M.K.; Njeru, R.W.; Kiarie, N.; Munyua, J.K.; Ateka, E.M.; Muinga, R.W.; Kapinga, R.E.; Lemaga, B.
    Sweetpotato is an important food, feed and cash crop in Eastern Africa. Highly stable and adaptable genotypes are important in sweetpotato productivity and evaluation across sites would form a basis for breeding varieties that are stable. Seventeen sweetpotato genotypes were evaluated for two seasons in three sites which have differentials in sweetpotato virus disease prevalence and climatic conditions in the coastal region of Kenya to determine their stability and adaptability in the region. The experimental design was randomized complete block design. Harvesting was done at four and half months after planting and tuber yield was determined. Data was analysed using the additive main effects and multiplicative interaction model (AMMI) to establish the genotype x environmental interactions (GEI). There was wide variation across the environments in the two seasons. Stability and adaptability was identified among sweetpotato genotypes. Varities Jonathan, Exshimba, SPK 004 and Kemb 10 were highly adapted across all the environments whereas Ejumula, Jewel, Jubilee, Bungoma, and sponge were stable. The highly adapted genotypes can be used as a basis for further improvement through breeding by crossing with the stable genotypes.
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    Evaluating diversity among Kenyan sweet potato genotypes using morphological and SSR markers
    (2010) Karuri, H.W.; Ateka, E.M.; Amata, R.; Nyende, A.B.; Muigai, A.W.T.; Mwasame, E.; Gichuki, S.T.
    Genetic diversity of 89 sweet potato genotypes was evaluated using morphological and molecular markers. Eighteen aerial and sixteen storage root characters were used in the morphological characterization. Analysis of variance showed that all the characters evaluated were significantly different (P<0.01) between the genotypes. The dendrogram obtained using phenotypic characters separated the genotypes into two major clusters with a Euclidean distance ranging from 0.0 to 6.98. Twenty three unique alleles, ranging from 3 to 6 per locus were detected using six simple sequence repeats (SSR) markers. Cluster analysis showed a Jaccard coefficient ranging from 0.5 to 1.0 indicating high genetic diversity. Comparison between morphological and molecular data using the mantel test revealed a low correlation (r = -0.05) between the two data sets. Despite the poor correlation both techniques showed a high degree of variation among the genotypes suggesting great genetic diversity in Kenyan sweet potato genotypes that can be utilized in breeding programs.
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    Mitochondrial DNA variation of Bemisia tabaci (gennadius) (hemiptera: aleyrodidae) infesting cassava in Kenya
    (2011) Atuncha, H.; Monjero, K.; Ateya, L.; Mbogo, I.; Mwirichia, Romano K.; Amata, R.; Ateka, E.M.
    Bemisia tabaci is a widely distributed crop pest affecting the yield of a broad range of agricultural, fiber, vegetableand ornamental crops. It is an extremely polyphagous pest that causes direct damage and can act as a vector ofviral plant diseases. Populations of Bemisia tabaci that are morphologically indistinguishable and with differentbiological traits have been known to exist; they show differences in rates of development, host range, insecticideresistance and virus transmission efficiencies. The objective of this study was to investigate the biotype identity ofB. tabaci infesting cassava in Kenya using the mitochondrial cytochrome oxidase I (mtCOI) sequence as a molecularmarker. The mitochondrion cytochrome oxidase one gene fragments were phyologenetically analyzed usingneighbor joining method. Results revealed two distinct haplotypes of cassava associated B. tabaci in Kenya. Thefirst haplotype consisted B. tabaci collected from the Eastern and Coast provinces of Kenya in a sub-cluster with 68boot strap value. They closely resembled B. tabaci genotypes from the southern parts of Africa (Mozambique,South Africa, Swaziland and Zambia) and B. tabaci isolate from West Africa (Ghana). The second haplotypecomprised of B. tabaci collected from cassava growing regions in Nyanza and Western provinces of Kenya in a subclusterwith 94 boot strap value. They shared close sequence homology with cassava B. tabaci from Uganda andTanzania. The findings of this study form part of important documentation on B. tabaci biotype status in Kenya forpest management purposes and for the prevention of invasive biotypes which may be more dangerous.
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    Survey of sweet potato viruses in Western Kenya and detection of cucumber mosaic virus.
    (2010) Opiyo, S.A.; Ateka, E.M.; Owuor, P.O.; Manguro, L.O.A.; Karuri, H.W.
    Sweet potato is an important food crop worldwide, but several pests and diseases limit its production. In eastern Africa, virus-induced diseases rank second to weevils in causing yield reduction. Symptomatic sweet potato cuttings (327) were collected from Nyanza and Western Provinces in western Kenya in 2009. The samples were tested for Sweet potato feathery mottle virus (SPFMV), Sweet potato chlorotic stunt virus (SPCSV), Sweet potato mild mottle virus (SPMMV), Sweet potato chlorotic fleck virus (SPCFV), Sweet potato latent virus (SPLV), Sweet potato caulimo-like virus (SPCa-LV), Cucumber mosaic virus (CMV), C-6, Sweet potato virus G (SPVG) and Sweet potato mild speckling virus (SPMSV) using nitrocellulose membrane enzyme-linked immunosorbent assay (NCM-ELISA). SPFMV, SPCSV, SPCFV, SPMMV and CMV were detected and 89% of the samples as a whole were found to be infected. SPFMV was detected in all infected samples followed by SPCSV (55%). Multiple infections were detected in the majority of the samples (80%) and the most common dual infection was with SPFMV and SPCSV (52%). The occurrence of CMV was low (5%) but was confirmed by RT-PCR with amplification of a 670 bp coat protein gene fragment from total RNA. This is the first record of CMV in sweet potato in Kenya