Wheat rust surveillance in South Africa – A molecular approach

Wheat production in South Africa is vulnerable to leaf-, stem- and stripe rust caused by Puccinia triticina, P. graminis f. sp. tritici , and P. striiformis f. sp. tritici , respectively. These diseases negatively affect both yield and quality of the crop. Annual surveys were initiated in South Africa during the early 1980s to monitor pathogenicity changes in the rust pathogens that could affect local wheat production. These conventional methods identified virulence changes based on phenotypes on differential lines carrying specific resistance genes. More recently, molecular tools have been used to study the genetic variability of the rust pathogens, which in turn complemented the traditional phenotyping assays. Genetic analysis confirmed that newly detected virulence is primarily due to either stepwise mutations within a genetic lineage, or foreign introductions into the country. Urediniospores of wheat rusts that originated in mid-Africa, not only spread to southern Africa, but may cross the Indian ocean to Australia on rare occasions and under certain climatological conditions. These findings emphasize the importance of the annual surveys, and the value added by genetic analysis of the three wheat rust populations.