Distribution of mating types of Ascochyta fabae f sp. lentis

The frequency, distribution, and virulence of two mating types of Ascochyta fabae f. sp. lentis were studied under controlled conditions. Crosses of 223 isolates from western Canada and 14 other lentil-growing countries of the world were made with mating type 1 and mating type 2 at 10 degrees C. Pseudothecia were observed on average after 17 days incubation. Both mating types were identified in samples from local and foreign sources with varying frequencies but mating type 1 was the more frequent. Mating type 2 was not identified in a large sample of the 1991 pathogen population from western Canada. Foreign isolates identified as mating type 2 originated from Algeria, Hungary, India, Russia, Spain, and the USA. Seven isolates of each mating type were tested on 10 lentil differentials in the growth chamber. There were significant differences among lentil differentials, isolates, and differential x isolate interactions for incubation period, latent period, and disease severity. The two most resistant differentials (ILL5588 and ILL5684) showed longer incubation and latent periods and low disease severity. Differential x isolate interactions contributed less to overall variation than differentials and isolates. The tests provided no evidence for major differences in virulence between the two mating types.