Development of pea bacterial blight caused by Pseudomonas syringae pv. pisi in winter and spring cultivars of combining peas (Pisum sativum) with different sowing dates

Summary Pea bacterial blight occurred by natural infection in a field trial on peas in 1995. Disease development in the winter cultivars Rafale, Frilene and Froidure was compared with that in the spring cultivars Baccara, Conquest and Bohatyr, each sown on six dates in October, November, December, mid‐March, late March and April. Disease incidence had reached 100% plants affected in all treatments by mid‐July. Disease severity 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 the winter‐sown plots in May and June and the spring cultivars were affected more severely than the winter cultivars. Comparison of areas under the disease progress curves for both disease incidence and severity also showed that the winter‐sown peas were more affected by disease than spring‐sown peas and that spring cultivars were more severely affected 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 tha‐1 occurred for each 10% increase in canopy area affected by pea bacterial blight.