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Reaction of selected common bean genotypes to physiological races of phaeoisariopsis griseola occuring in Kenya
IN Wagara, AW Mwangómbe, JW Kimenju, RA Buruchara, PM Kimani
African Crop Science Journal , 2011,
Abstract: The wide pathogenic variability occurring in Phaeoisariopsis griseola, the causal agent of angular leaf spot of common bean (Phaseolus vulgaris L.), dictates that new sources of resistance be continuously identified. This study was undertaken to determine the reaction of selected bean genotypes to different races of P. griseola in order to identify potential sources of resistance to angular leaf spot. Selected bean genotypes from Eastern and Central Africa Bean Research Network (ECABREN) and National Dryland Farming Research Centre (NDFRC), Katumani in Kenya were separately inoculated with forty-four races of P. griseola and evaluated for disease development under greenhouse conditions. The genotypes included small- and large-seeded types. None of the genotypes was resistant to all the races, indicating a high complexity of the pathogen population. Thirteen genotypes were resistant (disease score 1 to 3) or moderately resistant (score 4 to 6) to at least 40 of the races. Small- seeded bean genotypes ECAB 0754 and ECAB 0617 were resistant or moderately resistant to all races except Mesoamerican race 33-39 and Afro-Andean race 58-18, respectively. Genotype ECAB 0754 exhibited the highest level of resistance, with an average disease severity of 1.1%. All the resistant or moderately resistant genotypes were of the smallseeded bean types which are commercially less popular. The commonly grown large-seeded genotypes were generally susceptible. Among the bean genotypes evaluated, the small-seeded pintos and browns/yellows possessed high levels of resistance. The results of this study indicate that different bean genotypes have varying levels of resistance to angular leaf spot that can be pyramided into appropriate background to provide durable resistance.
Occurrence and Severity of Angular Leaf Spot of Common Bean in Kenya as Influenced by Geographical Location, Altitude and Agroecological Zones
A.W. Mwang`ombe,I.N. Wagara,J.W. Kimenju,R.A. Buruchara
Plant Pathology Journal , 2007,
Abstract: A survey to determine the prevalence, incidence and severity of angular leaf spot of common bean was conducted in Embu, Kakamega, Kiambu, Machakos and Taita Taveta districts of Kenya. The districts were selected based on the intensity of bean production, spatial and ecological location. Angular leaf spot was prevalent in all the districts and was recorded in 89% of the farms visited. The disease was present in all the farms surveyed in Embu, Kakamega and Machakos districts. In Taita Taveta and Kiambu districts, disease prevalence was 80 and 65%, respectively. The disease was prevalent across the lower midland, lower highland and upper midland agroecological zones and altitude ranges of 963-2322 m above sea level (m.a.s.l.). Disease incidence and severity were high (mean values of 49.6 and 21.4%, respectively) and varied significantly (p≤0.05) among districts, farms, agroecological zones and different altitudes. Kakamega and Taita Taveta districts recorded the highest disease incidence and severity, respectively, whereas Embu district had the lowest incidence and severity. Bean fields in the altitude ranges of below 1200 m and 1600-2000 m.a.s.l. had the highest disease severity (33.8%) and incidence (52.9%), respectively, whereas areas above 2000 m recorded lower disease levels. Agroecological zone LM2 and UM4 had the highest levels of disease incidence and severity whereas zones LH1 and UM3 had the lowest levels, respectively. These results indicate that angular leaf spot is severe and highly prevalent in Kenya. The disease spans across all the agroecological zones and altitude ranges where beans are grown. Efforts should, therefore, be geared towards an integrated approach to manage the disease.
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