Identification and evaluation of a critical time for assessment of slow rusting in pea against Uromyces fabae

Field and polyhouse studies were conducted to determine the appropriate time for the assessment of slow rusting in pea to Uromyces fabae (Pers de Bary). Early and late assessments of rust disease led to differential estimation of resistance under field conditions. The critical time occurred when disease severity on the susceptible (check) genotype HUVP 1 had crossed 90% but was <20% on the resistant (check) genotype FC 1. The rust response of germplasm lines at the critical time were in accordance with their known performances both in field and polyhouse. The disease assessment at critical time revealed precise differentiation between resistance and susceptible reactions in the F2 generation of the cross HUVP 1/FC 1. Moreover, AUDPC estimates based on only two disease assessments, including one assessment at the critical time provided comparable information to those based on six assessments. Reduction in 100-seed weight of inoculated F3 progeny rows showed high correlation with rust severity at the critical time and AUDPC based on two assessments in the field. Significant reduction in 100-seed weight was observed only for susceptible lines whereas, reductions in moderately resistant and resistant lines were not significant.