Influence of planting dates on the aggressiveness of common bunt races (Tilletia tritici and T. laevis) to Canadian spring wheat cultivars

Abstract

Cultivars varying in nonspecific resistance to common bunt were evaluated for their reaction to different races of Tilletia tritici and T. laevis following four different planting dates during 1987 and 1988. Percent bunted tillers decreased with successive planting dates from early April to late May. Percent infection in the highly susceptible cultivar HY320 was negatively associated with air and soil temperatures averaged over a 35-day period following seeding in both years. Most western Canadian spring wheat cultivars were resistant when planted during May but only Columbus was consistently rated resistant for all planting dates. However, in 1987, there was an increase in bunt levels in most cultivars on the May 25 planting date, and the highly susceptible cultivars HY320, Owens, and Fielder exhibited a susceptible reaction. Variability in aggressiveness was observed among races: T-19 was the most aggressive and L-16 was the least. The aggressiveness of races interacted with planting dates, indicating that aggressiveness of races was not stable over a range of environmental conditions. The implication of using a composite of races and early seeding for screening spring wheat cultivars for resistance to common bunt is discussed.

Keywords:

• Tilletia caries
• T foetida