Annual Research & Review in Biology

Common bean rust (Uromyces appendiculatus) is an etiological agent of bean rust disease of common beans (Phaseolus vulgaris L.) that causes damage and consequent yield losses. The high and wide virulence variability of the rust pathogen poses a major challenge to bean breeding programmes in Kenya with an objective of developing resistant varieties to the disease. This study was undertaken to identify Uromyces appendiculatus races and evaluate the virulence variability of Uromyces appendiculatus races occurring in common beans. The isolates were collected from Nyamira county and Narok South sub county, Kenya using transect line sampling method. Seven single pustule isolates obtained from the two counties were used to inoculate standard differential cultivars in a rust free green house to determine the physiological races of U. appendicultus. The application of a set of 12 standard differential cultivars and the international classification and binary nomenclature system grouped the seven isolates into four different U. appendiculatus races; 29-1, 29-3, 31-3 and 31-11. The race 31-11 was only prevalent in Nyamira county. The races affected the differential cultivars attributed to the Andean gene pool. The Meso american differential cultivars were resistant to most races of the rust pathogen. The races were found to vary in virulence based on their reaction with the standard differential cultivars. The findings from this study informs on the need for regular screening of bean genotypes for tolerance to bean rust as a strategy of effectively developing common bean  varieties with broad resistance to manage bean rust in Nyamira and Narok south, Kenya.