SURVEY FOR SEED-BORNE DISEASES ON WEED SPECIES FROM SCREENING SAMPLESOBTAINED FROM SEED CLEANING PLANTS ACROSS CANADA IN 1987 88/

In search for potential biological control agents for weeds, requests for samples of screenings from seed cleaning were sent out to seed cle aning plants across Canada in order to analyze for seed-borne diseases of weeds. Seven samples of screenings were received: two from Alberta , and one each from British Columbia, Saskatchewan, Manitoba, Ontario, and Prince Edward Island. A large percentage of the seeds (varying fr om 10 to 80%) developed fungal growth, of which very few affected germ inated seedlings. Pathogenic fungi were isolated from diseased seedlin gs of wild oats: Drechslera avenacea, cow cockle: Alternaria alternata , stinkweed: Alternaria raphani, green foxtail: Bipolaris sorokiniana, wild buckwheat: Botrytis sp., from western Canada, and from a grass s p.: B. sorokiniana, and red clover: Colletotrichum trifolii, from east ern Canada. These results show that surveys for weed diseases can be c onducted from samples of screenings submitted by cooperators. It is a quick and a relatively inexpensive method for weed disease surveying. However, as not all weed diseases are seed-borne, it cannot substitute surveys during the growing season.