Alfalfa seed is an important crop in many areas of western Canada. Blossom blight, caused by Botrytis cinerea and Sclerotinia sclerotiorum, is a serious constraint to production when cool, wet weather occurs during flowering. The symptoms caused by B. cinerea begin as small, water-soaked spots on blossoms. The spots coalesce rapidly, affecting the whole flower, and mycelium often grows from flower to flower, quickly attacking all of the flowers in a raceme.
Infected blossoms abscise prematurely without setting seed.
This disease has only recently been recognized in western Canada, so we were interested to determine if locally-adapted cultivars differed in disease reaction. The blight reaction of 12 alfalfa cultivars, representing a range of winter hardiness and plant architecture types, was evaluated in inoculated detached flower trials and growth cabinet tests in 1997-98. Similar differences were observed after 12 and 24 hours of incubation in tests using detached flowers under controlled conditions. However, all of the cultivars in the trial were at least moderately susceptible to infection. The impact of flower orientation and color on infection incidence was also assessed.