Variation in virulence within the cool temperature biotype of Stemphylium vesicarium (Wallr.) Simmons, a lucerne leaf spot pathogen

Abstract

This paper confirms the existence of variation in virulence within the cool temperature biotype of Stemphylium vesicarium, the causal agent of a lucerne leaf spot disease. The new strain shows high levels of virulence on an experimental line of lucerne (SS2) that was developed by selecting for resistance to S. vesicarium within the winter-active cultivar Sequel. The experimental line UC1250 (semi-dormant), which was bred for resistance in the U.S.A. and was resistant upon initial testing in Australia, remained relatively resistant to the new race, as did a selection (TS2) made from cv. Trifecta (semi-dormant). UC1249 (winter-active), which was also selected for resistance to S. vesicarium in . the U.S.A., was relatively susceptible to the new race.