Evaluation of winter wheat genotypes and seed treatments for control of dwarf bunt in Ontario

Dwarf bunt, caused by Tilletia controversa, is a destructive disease of winter wheat (Triticum aestivum) in Ontario. The development of resistant cultivars and identification of effective seed treatment fungicides would be beneficial for controlling this disease. Two hundred eighty-five selected cultivars and germplasm lines were evaluated in T controversa inoculated hill-plot field experiments and in the greenhouse from 2002 to 2005 to identify sources of resistance. Twenty-one genotypes, including the cultivars 'Blizzard', 'Carlisle', and 'Tarso, were identified with resistance to T controversa. To determine the efficacy of seed treatments, T controversa inoculated field trials were conducted at two locations in central Ontario for 3 years on eight winter wheat cultivars representing various market classes. The control agents included three rates of Dividend XL RTA (R) (difenoconazole + metalaxyl-M), Vitaflo-280 (R) (carbathiin + thiram), and bioagent ACM941, a strain of Clonostachys rosea. All seed treatments significantly (P <= 0.05) reduced disease incidence compared with the untreated controls. The three rates of Dividend XL RTA were all highly effective, providing 98%-99% control. Vitaflo-280 and ACM941 were partially effective, reducing disease incidence by 50% and 35%, respectively. The chemical seed treatments increased emergence by 5%-8% and yield by 2%-4%, which were significantly different from the untreated control. Bioagent ACM941 was less effective for disease control than the chemical seed treatments and had no effect on yield but increased emergence. There were no significant cultivar x Dividend XL RTA treatment interactions for all measured parameters, suggesting that it is an effective fungicide for controlling dwarf bunt in all winter wheat cultivars tested.