Soybean Research

Molecular diagnostics as a component of soybean rust sentinel plot program
DETECTION AND TRACKING OF THE AIRBORNE FUNGAL PATHOGEN PHAKOPSORA PACHYRHIZI FOR EARLY-WARNING DISEASE PREDICTION
Dr. Sarah Hambleton, Agriculture and Agri-Food Canada

Soybean production in North America has been threatened since the first confirmation in the southern United States (2004) of Asian Soybean Rust, a potentially devastating disease caused by the rust fungus Phakopsora pachyrhizi.

The Ontario Soybean Rust Sentinel Plot program was established in 2005 to monitor the potential spread of this disease into Canada through intensive scouting for symptoms and field evaluations in test plots. A molecular diagnostics component was implemented at AAFC to track the movement of airborne spores by screening samples from a network of rainfall and air collectors using a species-specific PCR-based DNA test. The first detection of soybean rust spores in Canada was during the 2007 growing season. In 2008, the network comprised 14 collection sites from Alberta to Quebec, including the collection and testing of samples from nine sites in Ontario.

Positive detections from a wide geographical distribution, from Saskatchewan to Eastern Ontario, occurred in late June/early July, while positive results for the remainder of the season were limited and scattered. Although there were several other periods of major storm activity into Canada, rust spore loads had not built up in the south due to unfavourable conditions for disease development. Spore trapping results were provided to OMAFRA for risk assessment and the development of management strategies if warranted. The results were also included in computer model analyses of North American sentinel plot data for disease forecasting.

Canadian production will be vulnerable if favourable environmental conditions result in the long range dispersal of viable spores from the US at the most critical time of crop development, during flowering. Real-time data for airborne pathogen spore dispersal patterns can be used to alert stakeholders of impending disease threats, in effect providing an early warning system to manage risk and avoid unnecessary fungicide applications.