MONOGENIC AND EPISTATIC RESISTANCE TO BEAN RUST INFECTION IN COMMON BEAN

In order to determine the relationship between resistance genes and hydrolytic enzyme induction, the interaction between two Phaseolus vulgaris cultivars (Sierra and Olathe) and two Uromyces appendiculatus races (47 and 55) were analyzed. Resistance of Sierra to race 55 was expressed as hypersensitive flecking, whereas the resistance of Olathe to race 47 was not associated with macroscopic symptoms and was classed as immunity. The Sierra/race 47 and Olathe/race 55 interactions were compatible. An analysis of a F-2 population and F-3 families demonstrated that a monogenic factor controlled resistance to race 47 while two genes controlled the interaction with race 55. At one locus determining resistance to race 58 resistance is dominant to susceptibility, and al the second locus hypersensitive resistance is dominant to immunity. Both alleles at the second locus are hypostatic to the susceptibility allele at the first locus. The induction of the hydrolytic enzymes beta-1,3-glucanase and chitinase was monitored for the four interactions over a ten-day period. For the compatible interactions, the hydrolytic enzyme activities increased slightly over time. This pattern was also noted for the Olathe/race 55 immune-resistance interaction. In contrast, the beta-1,3-glucanase and chitinase activity for the Sierra/race 55 hypersensitive-resistance interaction was significantly greater from day 2 through day 10. These results suggest the possibility that induction of hydrolytic enzyme activity may be associated with hypersensitive, but not immune resistance in the bean/bean rust interaction. (C) 1995 Academic Press Limited