COMPONENTS OF PARTIAL RESISTANCE IN PHASEOLUS BEANS AGAINST AN ETHIOPIAN ISOLATE OF BEAN RUST

Phaseolus bean cultivars, obtained from the Ethiopian national breeding programme, and cultivars widely grown in the country, 15 in total, were tested in a greenhouse for five components of partial resistance to one isolate of bean rust. The single-pustule isolate came from Ambo, a site where bean lines are tested against rust because the climate is conducive to bean rust. The components examined include latent period (LP(50)), infection efficiency (IE), sporulation capacity (SC), infectious period (IP) and pustule size (PS). Differences in cultivar responses were found for all PR components. Differences were largest, however, for infection efficiency and sporulation capacity. Cultivars Exrico 23, A 176, Veracruz 10 and BAT 1198 had a high level of PR to the isolate tested. Mexican 142, a widely grown cultivar in Ethiopia was intermediate, whereas Red Wolaita, an important cultivar in the south, showed a low level of PR. Linear correlations between LP(50) and IE, and between SC and PS were high. Linear correlations between IE, SC, or PS with IP were not significant. Though differences in cultivar response were found for all components, any one parameter may not suffice to explain the PR potential of a particular cultivar. The study suggests that latent period, infection efficiency and pustule size should be used in selection for PR. For the evaluation of large numbers of bean cultivars in the greenhouse, IE and PS are preferable to minimize labour requirements.