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New Wheat Leaf Rust Races Increasing in Ontario

We have received more reports of leaf rust in Vienna wheat but keep in mind rust levels still remain low in most of these fields but the warmer, humid and wet weather could favour further disease development. Ontario has been participating in a Canadian wheat leaf rust survey for many years through the direction of Dr. Brent McCallum with Agriculture and Agri-Food Canada who is located at the Cereal Research Centre in Winnipeg. The information collected in this project is critical to the employment or inclusion of effective leaf rust genes in Canadian and Ontario commercially available wheat varieties.

Preliminary results indicate a general trend across Canadian to more complex wheat leaf rust races very similar to what we have seen with Phytophthora sojae in soybeans. The most predominant races in Ontario (MLDS, TDBG and TDBJ) accounted for 45.4% of the leaf rust isolates in 2007 and as the overall Canadian graph illustrates these same three races have been increasing in frequency throughout Canada (71.5% of isolates in 2007) . As mentioned earlier these races are more complex and have the ability to bypass or infect varieties which were resistant or tolerant to leaf rust infection in the past. These new races could explain why certain varieties such as Vienna have seen a dramatic increase in susceptibility to leaf rust in a very short time (3 years).

Figure 1- The most common wheat leaf rust races continue to change in Canada. The predominant Canadian races such as MLDS, TDBG and TDBJ are becoming more frequent in the province as well. (Source- Brent McCallum, AAFC).