Variations in virulence and genome of Mycosphaerella pinodes isolates from field peas in central Alberta, Canada

Eighty-three isolates of Mycosphaerella pinodes collected from diseased field pea plants in central Alberta, Canada, in 2001 were analyzed for their virulence on ten field pea differentials (JI96, JI181, JI190, Eclipse, Carrera, Danto, Radley Miko, Espace, and Majoret). Genetic variation was detected by using the RAPD technique. Six pathotypes were classified according to the average lesion size caused by infection of the differentials. Pathotypes I and II comprised 45% of the isolates and had differential reactions on lines JI181 and JI190; the moderately susceptible cultivars Eclipse, Carrera and Danto were resistant to these two pathotypes, but susceptible to the other four pathotypes. The distribution of isolates causing various levels of disease on susceptible cultivars was near normal. JI96 and Radley were only susceptible to the most aggressive pathotype, V, which represented 7% of the population and also caused large lesions on all other differentials. The most aggressive isolates were mostly collected from the northwest area of central Alberta, where moisture levels are usually higher than in the southeast region. Most of the isolates (74%) from central Alberta displayed similar patterns of aggressiveness among the differential host cultivars. No correlation was found between grouping by genetic variation versus by pathotype.