Characterization of Ascochyta isolates and susceptibility of pea cultivarsto the ascochyta disease complex in Alberta

The relative virulence of 109 Ascochyta isolates collected from pea fields in Alberta from 1996 to 1998 were evaluated on 10-day-old seedlings by the excised leaf-assay technique. Twenty-eight isolates were avirulent, while t he others produced lesions of various sizes on pea leaves. DNA samples from 86 isolates were amplified by the RAPD technique using PCR with single pri mers. One dominant genotype of Ascochyta pisi was identified throughout Alb erta, but variations in virulence were not clearly differentiated by the RA PD technique. Five Ascochyta isolates, four virulent and one avirulent, wer e used to assess the susceptibility of 20 field pea cultivars available in Alberta, including 13 yellow types and seven green types. Based on symptom development, the yellow-type cultivars Swing, Eiffel and Delta, and the gre en-type cultivar Orb, were the most susceptible. Of yellow-type cultivars, Voyageur, Carneval and Montana were most resistant to Ascochyta infection.