Molecular quantification of pathogenic Fusarium spp. in soil to predict pea root rot risk in the field

Root rot of field pea causes severe yield loss in the Canadian prairies, where 1.5 million hectares of peas are grown annually. A recent survey revealed that 40 % of fields were positive for Aphanomyces euteiches, while 80-90 % were also infested with Fusarium spp. Pathogenicity tests indicated that while A. euteiches was the most damaging, F. avenaceum and F. solani were also highly virulent. To assess risk of root rot prior to planting peas, the relationship of DNA quantity of Fusarium spp. to inoculum potential and disease severity was evaluated. Soil was inoculated with increasing concentrations of Fusarium inoculum, and an aliquot was removed for DNA extractions prior to planting peas for root rot assessments. DNA quantity in soils was measured using real-time PCR assay, and F. avenaceum and F. solani DNA concentration was correlated to disease severity. This assay was then used to quantify DNA in soil and stubble collected from commercial field samples and related to root rot severity recorded during the growing season. F. avenaceum was detected in soil at concentrations that do not induce disease. However, concentrations in stubble from previously-grown crops were at disease-causing levels. Similar analysis is underway for F. solani. Results are being validated in pea fields during the 2016 growing season, and will be used to develop a soil test to predict risk of developing Fusarium root rot, in conjunction with A. euteiches quantification.