Two experiments were conducted to evaluate the influence of genetic resistance and wetness period on the infection and lesion development of common bean (Phaseolus vulgaris) rust. Susceptible, moderately resistant and resistant cultivars were subjected to 4, 8, 12, 16, 20 and 24 h of wetness periods after inoculation with Uromyces appendiculatus. The experiment was conducted in a growth chamber with 12h light/dark period, 22 ± 1 ºC and relative humidity of 70 to 80%. There were significant effects of genetic resistance and wetness periods on the pathogen infection and lesion development. Resistant cultivars did not presented lesions at any wetness period, while susceptible cultivars present an increased percentage of leaf area infected from 4 to 20 h, with a small decrease at the 24 h of wetness period. In these cultivars, the number of lesions increased up to 24 h of wetness. Moderately resistant cultivars also presented increases in leaf area infected and in the number of lesions up to 24 h of leaf wetness. There was no significant effect of 16, 20, and 24 h wetness duration in relation to leaf area infected or lesions per cm². A wetness period of 16 h with a temperature of 22 ± 1 ºC was sufficient for rust level resistance evaluation in common bean. Moderately resistant cultivars presented longer incubation and latent periods than suscetible cultivars. The percentage of sporulative lesions and susceptible lesions criteria better separate the cultivars into susceptible, moderately resistant, and resistant groups.
