STUDIES OF TILLETIA CONTRAVERSA, THE CAUSE OF DWARF BUNT OF WINTER WHEAT

The occurrence and distribution of dwarf bunt of winter wheat in Ontario since 1952 is noted. While the severity of the disease has not been great, indications are that it is present in most areas of the province where winter wheat is produced in quantity and thus is of concern particularly to growers of seed wheat.The germination of T. contraversa was studied with a view to determining the prerequisites for infection, and the development of dwarf bunt. Chlamydospores incubated on water agar and on ordinary soil at controlled temperatures between 0° and 15 °C. germinated only after incubation for 3 to 4 weeks at relatively low temperature, and required almost 8 weeks to reach a maximum of over 50% of the spores germinated.The germination process to the end point of sporidium development was dependent on light and a temperature about 5 °C. for maximum development. A slightly acid soil reaction favored spore germination, but soil moisture was a more critical factor.In field tests, a correlation was also shown to exist between temperature, light, and soil moisture, and the severity of dwarf bunt infection resulting in winter wheat seeded on infested soil. In continuing tests, chlamydospores have survived 3 years on the surface of soil with very little loss of viability.