Wiping Out White Mould In Soybeans

The problem is being addressed by a research team led by Daina Simmonds of Agriculture and Agri-Food Canada (AAFC). Other members of the team include AAFC's Elroy Cober, Terry Anderson, Pauline Donaldson, Sheryl Hubbard, Jiping Zhao, and Isabelle Joanisse, as well as University of Guelph Plant Agriculture Prof. Istvan Rajcan, and Sylvie Rioux of Laval University.

They've been working since 1996 to develop a transgenic soybean line that is resistant to a fungus called white mould, which reduces yields and costs about six million dollars each year. The team has transferred a wheat gene, which was discovered by Prof. Byron Lane of the University of Toronto, into soybean plants. This gene produces a protein called oxalate oxidase (OxO), which the team has found to be effective in preventing white mould.

White mould proliferates in cool, wet or humid weather, conditions that are typical in Ontario during late summer months. The fungus is a double-edged pathogen that affects soybean yields in two ways. White mould secretes an acid called oxalic acid, which weakens soybean plant cell walls and makes the cells more prone to infection. Once plant tissues are infected with white mould, seed growth and maturation are retarded, thus reducing yield. Fungus maturing on soybean plants also produce sclerotia -black pebble-like hard bodies - inside the stem of the plant. Sclerotia are then harvested with the soybean, reducing its market value.

There are currently no commercial soybean cultivars with a high level of resistance to white mould. A resistant soybean cultivar could benefit growers by improving yield and allowing recovery of clean seed (without sclerotia). Seed free of sclerotia are highly valued in food-grade soybeans, giving exporters a market advantage.

The ability of modified soybean plants to resist white mould was tested under growth-room conditions. For the study, soybean plants were wounded and then infected with the white mould pathogen. Plants modified with OxO showed greater resistance to fungal invasion than non-modified lines.

Two years of field-testing at Ottawa, Ste. Foy and Elora also confirmed that modified lines can effectively resist white mould invasion and contamination with sclerotia. But these varieties aren't completely resistant to white mould infection.

"A small number of plants still develop a low level of disease," says Simmonds. "Ultimately, our goal is to produce soybean lines with complete resistance to white mould."

The team will be introducing other defense genes into modified soybean lines to further improve resistance against white mould in the future.

This research was sponsored by the Ontario Soybean Growers and by the Ontario Research Enhancement Program, a $4-million federally funded research initiative administered by the Research Branch of AAFC with input from the agriculture and agri-food sector, universities and the province. OREP supports 25 research projects in universities and research centres across the province, with the University of Guelph as a major participant. Projects focus on two key areas identified by the agriculture and agri-food community:consumer demand for higher quality safe products and ensuring crop production management systems that are environmentally sustainab