Effects of light leaf spot (Pyrenopeziza brassicae) infection on canopy size and yield of winter oilseed rape (Brassica napus)

摘要

Mechanisms of yield loss from light leaf spot (LLS, Pyrenopeziza brassicae) and effects of tebuconazole fungicide regimes were examined in winter oilseed rape at Rothamsted in 1997/98. There was no evidence that light leaf spot decreased plant populations, although disease-related winter kill can decrease yield. The best light leaf spot control was with routine or autumn/spring applications of tebuconazole, with responses greater for cv. Bristol (susceptible) than cv. Capitol (resistant). Cv. Capitolhad a greater pod green area index (GAI, estimated from light interception measurements) than cv. Bristol and routine tebuconazole treatments produced largest GAIs for both cultivars. Cv. Capitol yielded more than cv. Bristol and routine treatments increased yield most (by 1.29 and 1.93 t ha~(-1), respectively). Other treatments increased yield, with best responses for treatments including a spring fungicide application. Yield was positively related to pod GAI in June, indicating that the main mechanism of yield loss from LLS was reduction in numbers of pods and canopy GAI (which reduced capacity to capture light).