Browsing by Author "Ombori, Omwoyo"

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    Determination of Stem Rust Ug99 Disease Severity in Selected Wheat Backcrosses in Kenya
    (2017-05) Tubei, Jackline E.; Ombori, Omwoyo; Njau, Peter N.; Njoka, Fredrick M.
    Stem rust (Puccinia graminis tritici) is a disease of economic importance in wheat (Triticum aestivum L.) worldwide. The objective of this study was to determine the disease severity of the BC1F1 plants in the nursery at Kenya Agricultural and Livestock Research Organization, Njoro. Kingbird (resistant) was crossed with Njoro Bw2 (susceptible) to obtain F1 plants. The F1 plants were backcrossed with Njoro Bw2 to obtain a BC1F1 progeny. Two hundred and forty seeds of the BC1F1 plants, twenty eight resistant and susceptible parents were planted in two replicates and the Modified Cobb’s Scale was used to record their disease severity scores. An excel work sheet programmed with the AUDPC formula was used to compute the Area Under Disease Progress Curve (AUDPC) values for BC1F1 plants. Variation of the disease severity scores and mean AUDPC among the wheat plants was analysed using Analysis of variance (ANOVA). Results showed 47.9% of resistant plants that portrayed the pseudo black chaff (PBC) trait had low disease severity mean scores ranging from 0 to 1.0414 with mean AUDPC values below 99.8. The resistant plants without PBC were 43.3 % and had disease severity mean score ranging from 0.9098 to 1.3686 with mean AUDPC values ranging from 99.8 to 260.The BC1F1 plants that showed susceptibility to stem rust disease were 21 (8.8 %) and had the highest disease severity mean score ranging from 1.3223 to 1.4914 with the highest mean AUDPC values ranging from 282.5 to 431.3. The ANOVA computation showed that, variation in the disease severity and in the mean AUDPC values among the individual plants (P < 0.001) was significant, but variation in mean AUDPC values from one replicate to another (P > 0.001) was not significant. The BC1F1 wheat plants showed a low disease severity score in the field indicating that these
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    Introgression of Stem Rust Resistance into Popular Kenyan Wheat Varieties to Improve Production
    (2018-02) Jackline, Tubei E.; Njoka, Fredrick M.; Ombori, Omwoyo; Njau, Peter N.
    Aim: The objective of this study was to assess the introgression of the stem rust resistance genes into the BC1F1 plants using molecular markers. Place and Duration of Study: Field experiments were carried out in a nursery, at Kenya Agricultural and Livestock Research Organization (KALRO) Njoro Centre, Nakuru, Kenya at 0.3ºS and 35.9ºE and 2185 m above sea level from June 2012 to December 2013. Laboratory work was carried out in the Biotechnology laboratory, KALRO Njoro. Methodology: Polymerase Chain Reaction (PCR) amplifications were carried out to assess the introgression of stem rust resistance genes into the BC1F1 plants. Analysis of genetic variation was done at each locus in terms of the number of alleles observed, heterozygosity, expected heterozygosity, Shannon's diversity index, genetic diversity and gene frequency using genetic analysis package POPGENE Version 1.32. The neighbouring joining method was used to construct a dendrogram from a distance matrix based on Sokal and Michener’s genetic distances, using MEGA4 software 1in Power Marker 3.25. Results: Amplification using PCR showed that wheat BC1F1 plants accessions NP3, NP12, NP89, NP163, NP192 and Kingbird were positive for the Lr34 gene while the susceptible plants and Njoro Bw2 were negative. Evaluation done on three molecular markers showed that CSLV34 was polymorphic across the BC1F1 plant accessions with a total of 2 alleles per locus. The 17 wheat BC1F1 plant accessions and their parents (Njoro Bw2 and Kingbird) were placed into 2 clusters using the markers as a result of introgression, considering that the clustering in this study was purposively based on the presence or absence of the resistance genes. This indicates that the Lr34 gene which is an APR gene was successfully introgressed into five BC1F1 accession plants (NP3, NP12, NP89, NP163 and NP192). Conclusion: The resistant BC1F1 accession plants (NP3, NP12, NP89, NP163 and NP192) showed success in the introgression of the Lr34 gene that gives resistance to stem rust at adult plant stage together with other minor genes including Sr2 and Lr46. These can further be developed in the field, multiplied and the seeds distributed to the farmers as they showed low disease severity to stem rust disease