Pathogenic variation of western Canadian isolates of Mycosphaerella pinodes on selected Pisum genotypes

Twenty-two pathotypes of Mycosphaerella pinodes were identified from 275 si ngle spore isolates collected from diseased field pea plants in western Can ada during 1994-96, based on their virulence on 21 differential pea genotyp es (89-195, Bohatyr, Century, Danto, Fortune, JI103, JI1089, JI174, JI181, JI190, JI252, JI296, JI45, JI64, JI96, Majoret, Mike, MP1164, Radley, Ricar do, Triumph). Pathotype 1, which was virulent on all 21 genotypes, was the most frequently detected and comprised 121 of 147 isolates collected in Man itoba, 66 of 76 isolates in Saskatchewan, and 41 of 52 isolates in Alberta. Pathotype 1 represented 74.6, 79.7 and 96.6% of all collections in 1994, 1 995, and 1996, respectively. Pathotype 2 was avirulent on cv. Danto and was the second most frequently detected, comprising 15 isolates. The remaining 20 pathotypes were detected infrequently and comprised one to five isolate s. Although Pathotype 1 was virulent on all pea genotypes, disease severity was significantly lower on cultivars Danto, Majoret, Radley, and JI64 than on the other differentiels. These genotypes are considered moderately resi stant to the disease and are useful sources of resistance for breeding prog rams in western Canada.