Blossom Blight Reaction of Alfalfa Cultivars in Growth Cabinet Trials
Zhiwen Lan and Bruce D. Gossen
Saskatoon Research Centre, Agriculture and Agri-Food Canada, Saskatoon, SK S7N 0X2
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. There were consistent differences among cultivars in degree of susceptibility; cvs DK 135, OAC Minto, and Iroquois were significantly less susceptible than cvs Algonquin, Apollo II and Heinrich. For example, in whole plant inoculation tests, the incidence of flower infection after 48 hours of incubation, of Iroquois, OAC Minto and DK 135 was 36%, 36% and 40%, respectively, and 75%, 79% and 71% for Algonquin, Apollo II and Heinrich. 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. Parallel studies are being conducted by Dr. Holley at Brooks AB. The impact of flower orientation and color on infection incidence was also assessed. Flowers of cv Vernal that faced upward had a much lower incidence of infection (16% infected) than downward facing flowers (86%). Purple flowers of cv Iroquois had a lower incidence of infection than white flowers (61% vs. 81%) after 24 hr incubation in a detached flower study, but there were no differences associated with flower color in Apollo II (purple vs. white flowers) or AC Nordica (purple vs. yellow). Trials are underway to assess cultivar reaction in field trials at Saskatoon SK and Brooks AB. It may be possible for growers in regions where blossom blight frequently occurs (e.g. the Peace River region of northern Alberta) to reduce the risk of serious yield loss by selecting cultivars that are less susceptible to blossom blight.
References
Gossen, B.D., Smith, S.R. and Platford, R.G. 1994. Botrytis cinerea blossom blight of alfalfa on the Canadian prairies. Plant Dis. 78: 1218
Holley, J.D. 1997. Assessing the potential of cultivar resistance as a control for alfalfa blossom blight. Pg. 15 in Proc. 18th Annual meeting Plant Pathol. Soc. of Alberta, Nov. 17-19, 1997, Brooks, AB.