Browsing by Author "Dida, Mathews M."

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    Exploring the Changes of Resistant Genes Expression in Groundnuts (Arachis Hypogea) In Response to Aspergillus Flavus Exposure at Seedling Stage
    (2020-07) Okayo, Robert O.; Andika, Darius O.; Dida, Mathews M.; K’Otuto, George O.; Gichimu, Bernard M.
    Aspergillus flavus infect groundnut seeds and produce secondary metabolites, aflatoxins. The aflatoxins are associated with various diseases in domestic animals and humans globally. Mitigating the aflatoxin contamination in crops through the development of cultivars tolerant to fungus colonization and aflatoxin contamination has been considered the most costeffective measure. This research was conducted to ascertain that the resistance genes identified in the previous transcriptome analysis were involved in groundnut defense mechanisms to A. flavus infection. Eight genes were selected for additional scrutiny through the real time PCR on a groundnut seedling at an interval of 2 days within a 7-day period. The results indicate a network of gene expression patterns in a sequential order in both resistance and susceptible lines at a seedling stage. The peak expression level per gene indicates the time gene action was crucial. We conclude that these genes are involved in groundnut resistance to A. flavus infection and provide important targets for the molecular marker screening.
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    Morphological and Molecular Characterization of Toxigenic Aspergillus flavus from Groundnut Kernels in Kenya
    (Hindawi, 2020-09) Okayo, Robert O.; Andika, Darius O.; Dida, Mathews M.; K’Otuto, George O.; Gichimu, Bernard M.
    Pathogenesis of Aspergillus flavus on important agricultural products is a key concern on human health due to the synthesis and secretion of the hazardous secondary metabolite, aflatoxin. &is study identified and further characterized aflatoxigenic A. flavus from groundnuts sampled from sundry shops in Kenya using integrated morphological and molecular approaches. &e groundnuts were plated on potato dextrose agar for isolation and morphological observation of A. flavus based on macroscopic and microscopic features. Molecular characterization was done through amplification and comparison of the partial sequence of the ITS1-5.8S-ITS2 region. &e expression analysis of aflR, aflS, aflD, aflP, and aflQ genes in the aflatoxin biosynthesis pathways was conducted to confirm the positive identification of A. flavus. &e gene expression also aided to delineate toxigenic isolates of A. flavus from atoxigenic ones. Morphologically, 18 isolates suspected to be A. flavus were identified. Out of these, 14 isolates successfully amplified the 500 bp ITS region of A. flavus or Aspergillus oryzae, while 4 isolates were not amplified. All the remaining 14 isolates expressed at least one of the aflatoxigenic genes but only 5 had all the genes expressed. Partial sequencing revealed that isolates 5, 11, 12, 13, and 15 had 99.2%, 97.6%, 98.4%, 97.5%, and 100% homology, respectively, to the A. flavus isolate LUOHE, ITS-5.8S-ITS2, obtained from the NCBI database. &e five isolates were accurate identification of atoxigenic A. flavus. Precise identification of toxigenic strains of A. flavus will be useful in establishing control strategies of the fungus in food products.
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    Morphological Characterization of Some Wild and Cultivated Watermelon (Citrullus Sp.) Accessions in Kenya
    (2009-03) Gichimu, Bernard M.; Owuor, B.O; Mwai, Gideon N.; Dida, Mathews M.
    Genetic diversity and relatedness were assessed among three most common commercial watermelon cultivars in Kenya; one newly introduced commercial cultivar from the U.S., one Kenyan landrace and one wild (Citrullus colocynthis) accession. The six accessions were grown in the field for two seasons under sub humid tropical conditions. Randomized Complete Block Design (RCBD) with three replications was used. Data was collected on morphological features of watermelon which include vine, leaf, flower, fruit and seed characteristics. A descriptor list with 21 morphological (qualitative and quantitative) characters was adopted from Diez et al., (2005) and Jarret and Griffin, (2007) and was refined and used in characterization. The data was used to calculate genetic similarity and to construct a dendrogram using the unweighted pair-group method with arithmetic average (UPGMA). Data on quantitative characters was subjected to Analysis of Variance (ANOVA) using SAS statistical package and effects declared significant at 5% level. The procedure PRINCOMP was then used to perform a principle component (PC) analysis using six quantitative variables and accessions plotted on two dimensions using the first two principle components (PC1 and PC2). The cluster analysis results demonstrated high morphological diversity (54-42%) between unimproved accessions (wild accession and landrace) and commercial cultivars and low morphological diversity (8-27%) among commercial cultivars. The ANOVA conducted on quantitative characters of cultivated accessions demonstrated highly significant variation between accessions. Results of the principle component analyses for the six quantitative traits indicated that the first two PCs explained 68% and 29% (a total of 97%) of the total variation. The low morphological diversity observed among commercial cultivars emphasizes the need to expand the genetic base of the cultivated watermelon in Kenya.