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Project Abstract: Investigating Ways to Improve Management of Root Rot in Soybeans

Root rot is a serious disease of soybean in Canada for which successful control has been elusive. A preliminary examination of soybean roots collected from selected fields in Manitoba and Alberta in 2012 indicated that the predominant pathogens isolated from infected roots were Fusarium spp. The long-term, most economical approach for managing Fusarium root rot is the use of resistant cultivars, but no cultivars with a high level of resistance are available. In Manitoba during 2011-2012, isolations from diseased soybean roots also indicated the presence of Phytophthora spp. Little information was available in western Canada on the prevalence, incidence and pathogenicity of Phytophthora root rot, which is one of the most destructive diseases of soybeans in Ontario. On the Canadian prairies dryland salinity is a major soil degradation problem and can impact crop yield, but whether this predisposes soybean plants to root rot is unknown.

The soybean root rot project includes four research objectives led by researchers at Agriculture and Agri-Food Canada, Alberta Agriculture and Forestry and the University of Alberta. The specific objectives of the study were developed to align with the industry priorities of ensuring that soybean producers have access to high yielding, disease resistant varieties that are adapted to growing conditions in western Canada. These objectives are: 1) To determine the impact of root rot pathogens on yield loss of soybeans in western Canada; 2) To identify the major root rot pathogens of soybean in western Canada; 3) To measure the genetic variation within the populations of soybean root rot pathogens and assess the impact of soil salinity on root rot development and 4) To identify short season soybean cultivars that are resistant to the Fusarium and Phytophthora spp. that occur in western Canada.

Field trials to assess yield loss due to root rot pathogens, surveys of commercial soybean crops for root diseases, research on the development of molecular techniques for pathogen identification and field trials to evaluate soybean cultivars for resistance to root rot pathogens were conducted to achieve the above objectives. The predominant Fusarium spp. associated with soybean root rot in western Canada were identified based on surveys of soybean crops and assessment of diseased roots using conventional and novel molecular diagnostic approaches. All Fusarium spp. generally had a similar impact on productivity with a 10% reduction in yield at Brandon (2016) following inoculation with the root pathogens.

Results from testing soybean cultivars for their response to root rot in saline soil suggest that salinity stress may directly affect the susceptibility of root tissues to pathogen invasion. Differences in the response of soybean cultivars to several root pathogens were observed in screening studies conducted in the field and greenhouse. New information on the identity of soybean cultivars with partial resistance to seedling blight and root rot will enhance breeding activities to develop new soybean cultivars with high levels of resistance to several root pathogens. Using a set of differential cultivars, the common race of Phytophthora sojae in Manitoba was identified as race 4.

As soybean acreage continues to increase across western Canada, there will be selection pressure for the development of new races of the pathogen and continuous monitoring of race diversity and distribution is an important factor for managing phytophthora rot of soybean.

 

For more information, contact Dr. Debra McLaren   (204) 578-6524   debra.mclaren@agr.gc.ca 

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