This study assesses the importance of infection from soil. It also investigates the conditions that affect the success of infection, especially under the influence of quantitative resistance (QR) and fungicide seed treatment. The information will help understand how relevant this infection route is to blackleg incidence and whether a fungicide seed treatment can mitigate this.
Experiments conducted under controlled conditions showed that blackleg can be caused by soil inoculum at levels higher than 1,000 spores per gram of soil. Wounding roots exacerbated the infection, and this indicates that root injuries by other factors (diseases or insects) may increase the infection from soil inoculum. Current seed treatments did not control the infection from soil but a newly registered seed-treatment product appeared effective. Our next step is to develop a PCR-based protocol to quantify the inoculum level in commercial fields to better understand the risk for infection from soil on the prairies.