CFCRA Cropping Systems Cluster: Activity 7 – A pan-Canadian approach to improving soybean Sclerotinia stem rot resistance

Objectives:

• Identify and map Sclerotinia sclerotiorum (soybean stem rot (SSR) pathogen) populations across Canada, evaluate their virulence, and develop genomic tools for the assessment of sclerotiorum isolates to identify a representative multi-isolate S. sclerotiorum panel representing genetic and virulence diversity from across Canada.
• Evaluate resistance in commonly used short season soybean parental varieties against a subset of representative sclerotiorum isolates and compare to the Québec registration trial isolate NB-5 to identify parents with reliably stable resistance.

Impacts:

• Increased understanding of sclerotiorum genetics and diversity across Canada.
• Identification and utilization of suitable SSR isolates for soybean resistance screening programs.
• Design reliable SSR screening methods for readily available implementation into Canada’s SSR nurseries.
• Development of a diverse soybean check panel for maturity group (MG) 0, MG 00, and MG 000 and sclerotiorum isolates for improved evaluation of soybean SSR resistance.
• Identification of suitable parents for stable resistance to SSR and utilization of these parents in soybean breeding programs.

Scientific Summary:

The use of resistant varieties is among the most effective options for minimizing risks associated with soybean Sclerotinia stem rot (SSR) caused by Sclerotinia sclerotiorum. Recent studies demonstrate that soybean resistance can be greatly affected by the S. sclerotiorum isolate used for evaluation, with resistance ranging from susceptible to moderately resistant within a single soybean or canola line. These shortcomings may seriously compromise the efficiency and stability of SSR nursery evaluations as isolates used vary from nursery to nursery, potentially leading to inconsistencies in cultivar evaluations. This may result in variable cultivar responses in the field for the control of soybean SSR, resulting in increased losses or increased reliance on fungicides due to climate change and the growing soybean sector. Additionally, the use of susceptible varieties increases inoculum load in fields, putting at risk other susceptible crops such as canola, sunflower, and legumes. Adding soybean to crop rotations helps reduce greenhouse gas (GHG) emissions via its ability to fix nitrogen (N), but its inclusion in rotations should not compromise other crops. A comprehensive approach to improving and stabilizing soybean SSR nursery evaluations and closing the gap in inconsistencies in resistance levels observed for some soybean varieties will produce stable and reliable evaluations of soybean resistance to SSR, reduce SSR inoculum loads, and help reduce the reliance on fungicides for soybean and other susceptible crops in the rotation.

The experimental approach used to fulfill the objectives will be:

1) Collect and identify S. sclerotiorum populations across Western and Eastern Canada.

2) Selection of a representative S. sclerotiorum multi-isolate panel through resistance and genetic screening on commonly used checks.

3) Assess short season parental varieties against representative isolates to evaluate the degree of resistance against isolates from across Canada.

The direct benefits of this project are that SSR nurseries will be stabilized using multi-isolate screening of isolates representative of S. sclerotiorum diversity across Canada and increasing the profitability of growers due to reliable soybean resistance screening methods.

Using disease loss estimates, SSR causes $20 M in annual losses in Ontario and approximately $41 M across Canada. By stabilizing resistance through improved SSR nursery screening and identifying reliable soybean SSR resistance sources, we estimate that losses due to SSR can eventually be reduced by at least 10%, representing average gains of $2.4 M and up to $3.4 M in epidemic years.

External Funding Partners:

This activity was funded in part by the Government of Canada under the Sustainable Canadian Agricultural Partnership’s AgriScience Program, with industry support from the Canadian Field Crop Research Alliance (CFCRA) whose members include: Atlantic Grains Council; Producteurs de grains du Quebec; Grain Farmers of Ontario; Manitoba Corn Growers Association; Manitoba Pulse & Soybean Growers; Saskatchewan Pulse Growers; Prairie Oat Growers Association; SeCan; and FP Genetics.