Coffee leaf rust (CLR), caused by the fungus Hemileia vastatrix, is among the most important diseases affecting coffee all over the world. In Kenya, it is currently the second most important disease, and breeding coffee to obtain new resistant cultivars has been a priority. Over time, new rust pathogenic races able to infect hitherto resistant coffee genotypes have been registered. To date, 49 races of the pathogen have been characterized all over the world. The most recent races to be characterized are able to infect derivatives of Timor Hybrid (HDT), which is a major source of resistance in breeding programs. This work aimed to identify new races of the pathogen in Kenya, emphasizing infected leaves sampled from CLR resistant varieties and breeding lines collected from two sites (Ruiru and Koru). Twenty-four samples were characterized, out of which 22 samples corresponded to new races of the pathogen. A total of six new races (III, XVII, XXIII, XXXVI, XLI and XLII) were characterized, revealing three new virulence genes (v 1 , v 7 , v 8 ) and possibly a fourth virulence gene, the v 9 . This finding represents a serious threat to coffee production and also a challenge to coffee breeding programs that are in progress in Kenya.
Coffee supports livelihoods of approximately 125 million families worldwide and over 700,000 households in Kenya. The epidemics of Coffee berry disease (CBD), caused by Colletotrichum kahawae, destroy up to 80% of the developing berries on susceptible varieties. The control of the disease using chemicals accounts for 30 to 40% of the production cost and contributes to environment pollution, hence the use of resistant varieties. Resistance to CBD is conferred by three genes; R, T that are dominant and k which is recessive, from coffee varieties Rume Sudan (RS), Hibrido de Timor (HDT) and K7 respectively. Although the T gene has been mapped, there is need for genetic mapping of the other genes to improve selection efficiency. The objective of this study was to evaluate F2 populations of RS x SL28 for their suitability to genetic mapping of the R gene in RS. Resistance to CBD was evaluated by hypocotyl inoculation on their F3 progenies. The data was subjected to Analysis of Variance (ANOVA) and Chi Square (χ²) test. The ANOVA result showed significant differences (P≤0.05) between the genotypes to CBD resistance. The phenotypic ratio of resistance to susceptible plants fitted the 3:1 monohybrid inheritance ratio for a dominant gene using the χ² test (χ² = 1.0565 and P=0.30207, P≤0.05), hence confirming the suitability of the F2 populations for the identification of the DNA marker for R gene in RS.
Given the immense damage and yield loss due to bacterial blight of coffee disease that is caused by Pseudomonas syringae pathovar garcae, this study sought to evaluate the diversity associated to the virulence of Psg isolates on coffee in Kenya. Twelve strains of Psg pathogen were collected from different coffee growing regions in Kenya and characterized using both phenotypic (host-pathogen interaction via laboratory inoculation) and molecular tools using and genomic sequencing. The sequencing was done using 16S ribosomal RNA primers 8 F and 1492 R and sequences were then retrieved for alignment and phylogenetic analysis using MEGA 6 via clustalW. The results revealed high variability of Psg isolates and possible existence of several races of P. s. garcae species. The study provides new knowledge on the nature of virulence of BBC pathogen, and a platform towards breeding for coffee with durable disease resistance in Kenya.
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