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Oospore dose-response and spatial distribution of the pea root rot pathogen, Aphanomyces euteiches, in Saskatchewan soils

S. Chatterton, A. Erickson, and S. Banniza. Oospore dose-response and spatial distribution of the pea root rot pathogen, Aphanomyces euteiches, in Saskatchewan soils. Annual Meeting of the Canadian Phytopathological Society, Moncton NB, June 12 – 15, 2016. (oral presentation)

Abstract

Aphanomyces root rot, caused by Aphanomyces euteiches Drechs., was first detected in pea fields in Saskatchewan and Alberta in 2012 and 2013, respectively, and can cause significant crop loss in both provinces. In order to determine oospore dose-response relationships, soils were collected from brown, dark brown and black soil zones in Saskatchewan, and sterilized or used as is (raw). Oospores were added to soils to provide final concentrations from 0 - 2000 oospores/g soil, A. euteiches DNA quantified using real-time PCR (qPCR), and then used to grow pea plants for root rot assessments. The threshold level for disease in raw soils was 100 oospores/g soil in all soil types, which was also the limit of detection using qPCR. For black and brown soil types, the threshold level for disease was 750 oospores/g soil in sterilized soils, demonstrating that other soilborne microorganism increase disease risk. To determine spatial distribution of oospores in the field, soils were collected from 0-20, 20-40 and 40-60 cm depths at 11 sites from 3 pea fields in each of the 3 soil zones in Saskatchewan. Peas were grown in each soil sample and rated for root rot. Disease levels were highest in the top 0-20 cm layer, and decreased with increasing depth. Horizontal distribution of A. euteiches varied between fields. Real-time PCR analysis to quantify A. euteiches DNA levels in these soil samples is underway. Results will be used to develop sampling protocols and soil tests to determine root rot risk.

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