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Incidence of Botrytis cinerea and Sclerotinia sclerotiorum in seed alfalfa fields of southern Alberta
J. REICH (1), D. Johnson (1), S. Chatterton (2). (1) University of Lethbridge, Lethbridge, AB, Canada; (2) Agriculture and Agri-Food Canada, Lethbridge, AB, Canada

In cool, moist conditions, blossom blight of seed alfalfa, caused by the fungal pathogens <i>Botrytis cinerea</i> Pers.:Fr. and <i>Sclerotinia sclerotiorum</i> (Lib.) de Bary<i>,</i> are the largest contributors to seed yield losses in western Canada. Recently, growers in southern Alberta, the largest seed alfalfa production area in Canada, have experienced reduced seed yields without obvious symptoms of blossom blight. To determine whether blossom blight pathogens may be associated with yield losses, surveys were performed every 2-3 weeks in 19 seed alfalfa fields in the region. Visual ratings of severity and incidence were assigned in the fields, and flower and/or pod samples were plated on selective media. Based on field observations, blossom blight was present at trace levels. Plated samples revealed that, in all fields surveyed, <i>B. cinerea</i> infected 65% of florets at the beginning of July, and levels increased steadily to nearly 100% infected pods at the end of August. In all fields surveyed, <i>S. sclerotiorum</i> infected 10% of florets at the beginning of July, levels peaked in pods at 20% at the end of July, and declined to <10% by the end of August. <i>B. cinerea </i>infected 15% of harvested seeds, but no infection by <i>S. sclerotiorum </i>was observed. Results indicate that <i>B. cinerea</i> inoculum persists throughout the growing season on symptomless plant tissues. Greenhouse studies are under way to determine the impact of symptomless infection by <i>B. cinerea</i> on seed development and yield.

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