Virulence of Ascochyta fabae f sp. lentis on lentil

Virulence patterns of Ascochyta fabae f. sp. lentis were determined by testing 84 isolates collected from western Canada and 16 isolates from 13 other countries on 10 lentil lines and cultivars (differentials). Western Canadian isolates collected in 1978 and 1985 were less virulent than 1992 collections. The greatest difference was observed on the widely grown cv. Laird, which changed from moderately resistant to the 1978 isolates to susceptible to 1992 isolates. Cluster analysis grouped the isolates into weak, intermediate, and high virulence forms (Clusters 1-3). The virulence pattern did not relate to specific geographic locations. Foreign isolates were present in all three groups. Both analyses of variance and cluster analysis showed a general lack of specific host differential x isolate interactions, suggesting the absence of cultivar specificity. Principal components analysis confirmed that the major trend in the data was a continuum of increasing virulence among isolates from Cluster 1 to Cluster 3.