Epidemiology of bean rust in Ethiopia.

Field and greenhouse experiments were conducted to study the epidemiology of rust ( Uromyces appendiculatus ) on beans ( Phaseolus vulgaris L.) in Ethiopia. The experiments were conducted under low input conditions reflecting the traditional bean production practices. Surveys identified five major diseases. Bean rust, bacterial blight and anthracnose were widely distributed. Angular and floury leaf spots were prominent in the humid west. Disease severities depended on regions, cropping practices and seasons. Strong associations between sowing date and rust severity and between bacterial blight and weediness or plant density were found. Artificial differences in rust epidemics produced large differences in crop growth, yield and yield loss. Multiple regression models were developed to estimate yield and yield loss. Yield and yield loss were best estimated by leaf area index and rust severity during flowering and late pod setting stages. Differences were found in the velocity of focus expansion (3 to 16 cm day <sup>-1</SUP>) when susceptible and resistant bean cultivars were mixed at different proportions. The velocity of focus expansion increased linearly with the logarithm of the fraction of susceptible in the mixture. Five components of partial resistance were evaluated in a bean rust pathosystem. Differences between cultivars were largest for infection efficiency and sporulation capacity. Correlations existed between latency period and infection efficiency, infection efficiency and pustule size, and sporulation capacity and pustule size. Latency period, infection efficiency and pustule size can be used in screening for partial resistance