Significance of seed infection on epidemics of mycosphaerella blight in field pea

Mycosphaerella blight (Mycosphaerella pinodes) is the most important disease of field pea (Pisum sativum) in western Canada, occurring in almost every field each year. The objective of the study was to assess the impact of seed infection on epidemics of mycosphaerella blight. In preparation for the trial, seed lots of a susceptible and partially resistant cultivar with different levels of seed infection with M. pinodes were produced at a single site with uniform handling and storage conditions. Field trials were conducted in 2005 and 2006 at three sites in western Canada where levels of external inoculum were high (Vegreville, AB, Saskatoon, SK, Morden, MB), and one site (Bradford, ON) with little external inoculum. For each cultivar, the seed infection treatments were: (i) high seed infection (26-47% of seed infected with M. pinodes); (ii) intermediate seed infection (6-15% of seed infected); (iii) fungicide - intermediate seed lot treated with a fungicide to minimize seed transmission; and (iv) low seed infection (0-2% of seed infected). Seedling establishment was higher in the low seed infection treatment than the other treatments in four of eight station years, but there were no consistent differences among the other treatments. There were small differences in blight severity among treatments in several station years, but no differences were observed at Bradford, the site with minimal external inoculum. We conclude that seed infection with M. pinodes does not contribute substantially to above-ground symptoms in the year of planting. However, very high levels of seed infection reduced seedling establishment, so continued seed testing for germination is recommended. © Her Majesty the Queen in Right of Canada.