DEVELOPMENT OF PEA BACTERIAL-BLIGHT CAUSED BY PSEUDOMONAS-SYRINGAE PVPISI IN WINTER AND SPRING CULTIVARS OF COMBINING PEAS (PISUM-SATIVUM)WITH DIFFERENT SOWING DATES

Pea bacterial blight occurred by natural infection in a field trial on peas in 1995. Disease development in the winter cultivars Rafale, Fri lene and Froidure was compared with that in the spring cultivars Bacca ra, Conquest and Bohatyr, each sown on six dates in October, November, December, mid-March, late March and April. Disease incidence had reac hed 100% plants affected in all treatments by mid-July. Disease severi ty was greater in winter-sown (October, November or December) than in spring-sown peas of each cultivar at each assessment. Significant (P < 0.05) differences in disease severity occurred between cultivars in t he winter-sown plots in May and June and the spring cultivars were aff ected more severely than the winter cultivars. Comparison of areas und er the disease progress curves for both disease incidence and severity also showed that the winter-sown peas were more affected by disease t han spring-sown peas and that spring cultivars were more severely affe cted than winter cultivars. Yield was strongly correlated with disease severity. A Linear regression model suggested that, for peas sown in October, November or December, a yield loss of 0.5 t ha(-1) occurred f or each 10% increase in canopy area affected by pea bacterial blight.