Dwarf Bunt (Tilletia controversa )

Dwarf Bunt: biology

Dwarf bunt is caused by the fungus Tilletia controversa. It can affect wheat, winter barley, rye and triticale but has its greatest impact on winter wheat. The disease can be both seed-borne or soil-borne and may live for up to 10 years in soil.

Infection takes place from December to February. Once the fungus infects the plant, it grows systemically throughout the plant and in spring, replaces kernels with bunt balls. Favoured by cool soil temperatures, it is found in Ontario and interior British Columbia in areas with prolonged snow cover. There has never been a reported case on the Prairies, likely because the Prairie winters are too cold for its establishment.

Dwarf bunt will cause excessive tillering and stunting of the plant. Leaf lesions begin on the lowest leaves and tend to be irregular in shape, becoming pale, straw coloured and slightly necrotic (more common on winter wheat). It can cause loss of both yield and grade. In severe years, some fields have over 50% bunt-infected plants.

When infected grain is harvested or crushed, bunt balls rupture, releasing their spore contents and, contaminate the grain. The pungent, fishy odour of the spores is another characteristic of the disease. The spore cloud and the distinctive odour are the first signs that a crop may have the disease. Many importing countries have zero tolerance for bunt-contaminated wheat shipments.