Browsing by Author "Omondi, Chrispine"

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    Leveraging on germplasm acquisition for Arabica coffee improvement in Kenya
    (Scienceweb Publishing, 2016-01) Gichimu, Bernard M.; Omondi, Chrispine; Cheserek, Jane; Gimase, James
    The low genetic variability within Coffea arabica species is a major hindrance to its improvement. The emergence of new pathogen races, especially for the prevalent fungus Hemileia vastatrix causing Coffee Leaf Rust (CLR) is a challenge to coffee production worldwide. Two accessions, namely Selection 5A and Selection 6 were received in 2008 from India as part of germplasm exchange in a Coffee Leaf Rust collaborative project involving India and four African countries namely, Uganda, Zimbabwe, Rwanda and Kenya. Seedlings of two Kenyan commercial varieties SL 28 and Ruiru 11 representing susceptible and resistant varieties respectively were also raised alongside the Indian accessions. The seedlings of the four varieties were planted at Coffee Research Institute (CRI) sub-centre in Kisii country and Agricultural Training Centre in Machakos country for field evaluation. Data was recorded on growth and yield parameters before and after crop bearing. Field records were also taken for infection by Coffee Berry Disease (CBD) and Coffee Leaf Rust (CLR). Growth parameters related to crop bearing had stronger correlation with actual berry count and hence yield confirming that potential yield of a coffee variety can accurately be predicted by combining early measurements of growth parameters and yield records. The yield potential of the Indian accessions was found to be lower than the standard Kenyan varieties. However, the accessions were outstandi ng in resistance to CLR which was only comparable to the resistant Ruiru 11 variety. The study confirmed that CLR, if not controlled can erode the high yield potential of elite varieties if conditions are favorable. It was also concluded that the Indian accessions provides an opportunity upon which traditional Kenyan commercial cultivars can be improved to withstand existing and new races of the rust pathogen.
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    Pathogenicity of Colletotrichumkahawae in Kenya
    (2017-05) Njoka, Fredrick M.; Owaka, Margaret; Omondi, Chrispine; Kathurima, Elijah
    This study was aimed at determining the virulence diversity of Colletotrichumkahawae, and their correlation with coffee growing regions and interaction with coffee varieties in Kenya. A total of 34 single conidia isolates were obtained and subjected to variation analysis using DNA banding patterns. The test varieties included Rume Sudan, Catimor, K7 and SL 28 (susceptible). Seedlings were individually scored for disease symptoms and mean grade of infection was computed. The mean grade data was then used to perform Analysis of Variance (ANOVA) using the random effects model. The results were used to determine the correlation between molecular polymorphism and diversity in virulence. The variety x isolate interaction effects although significant (p<0.05) did not conclusively reveal the existence of races because the isolate effect was not significant. The virulence tests revealed that variation was due to main effects of varieties. Rume Sudan was highly resistant with a mean grade of 4.75. Catimor with a mean grade of 7.66 showed medium resistance. K-7 showed medium resistance with a mean grade of 9.97. SL 28 was highly susceptible with a mean grade of 11.75. The growing regions had no influence on the genetic and virulence diversity since C. kahawae isolates from all regions were pathogenic on the tested coffee cultivars. All the isolates were significantly (p<0.05) more aggressive on coffee cultivar SL28, followed by K7 and Catimor in that order. Rume Sudan showed high resistance to all the tested isolates irrespective of the region. It is concluded that variation in Colletotrichumkahawae population is largely due to differences in aggressiveness of the isolates.
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    Quantitative trait loci (QTL) mapping of resistance to coffee berry disease (Colletotrichum kahawae Waller & Bridge) in Coffea arabica L. variety Rume Sudan
    (Academic Journals, 2020-06) Gimase, James M.; Thagana, Wilson M.; Omondi, Chrispine; Cheserek, Jane Jerono; Gichimu, Bernard M.; Gichuru, E. K.
    Coffee Berry Disease (CBD) is a major constraint that limits Coffea arabica production, whose resistance is governed by three genes, T, R that are dominant and recessive k in varieties Hibrido de Timor (HDT), Rume Sudan (RS) and K7 respectively. This study identified the genomic region occupied by R-gene using F2 genotypes from varieties RS and SL28; and Single Nucleotide Polymorphic (SNP) markers obtained through Genotyping by Sequencing. Redundant markers were removed and 699 markers obtained for linkage mapping and quantitative trait loci (QTL) analysis. The Linkage map spread over 5525.39 cM across eleven coffee chromosomes (Chr). The QTL was analyzed by both Interval Mapping (IM) and Inclusive Composite Interval Mapping (ICIM) using SNP markers and CBD resistance mean scores of the F2 genotypes and their parents. Three QTLs, qCBD 1-1 in Chr 1, qCBD 2-1 and qCBD 2-2 in Chr 2 were significantly associated with CBD resistance, detected by both IM and ICIM at LOD ≥ 2.5 (P≤0.05). Two flanking markers that were closer to the three QTLs; 100025973|F|0-59:T>C59:T>C at a distance of 3 centi Morgans (cM) from qCBD 1-1 and 100034991|F|0-44:C>T-44:C>T, that was flanking in both qCBD 2-1 and qCBD 2-2 at 12.5 cM, whose SNPs were significant (P≤0.05), are recommended for validation and use in marker-assisted breeding.