Infectivity model for Aphanomyces euteiches in Saskatchewan soils

Aphanomyces root rot was recently detected in pea fields in Alberta and Saskatchewan, and has become a serious threat to sustainable pea and lentil production in the Prairies. Aphanomyces euteiches survives in soil as resilient thick-walled oospores, which are produced in decaying root tissues after infection. The threshold level for disease in raw soils was 50-100 oospores/g soil in all soil types, and severe root rot was observed at above 500 oospores/g soil. Dark brown soils were the most conducive to disease development. The presence of other soilborne microorganisms, such as Fusarium species, increases disease risk. The limit of detection needs improvement so that fields with oospore levels below 100 oospores/g soil do not return false negatives. Disease levels were highest in the top 0-20 cm layer, and decreased with increasing depth. However, horizontal distribution of A. euteiches varied between fields, with some fields showing uniform distribution throughout the 11 sampling sites, and other fields showing a patchy distribution between sites. Our results suggest that assessment of field history and landscape is sufficient to identify sites with A. euteiches inoculum for soil sampling, and that a specific sampling pattern is not required. Further refinement of DNA extraction protocols from different soil types to improve the oospore detection limit is needed to develop a decision support system.