Sclerotinia disease severity and sclerotia formation in various cover crops, flower strips, and weed species inoculated with diverse isolates of Sclerotinia sclerotiorum

Abstract: Cover crops and flower strips are used in agricultural fields as components of
integrated pest management strategies. However, their potential role as secondary hosts of
soilborne pathogens such as Sclerotinia sclerotiorum in oilseed rape cultivation remains
incompletely understood. In this present study, we assessed the impact of pathogen virulence on the progression of Sclerotinia stem/leaf rot and sclerotia production across 33 plant species belonging to 11 botanical families, utilizing two S. sclerotiorum isolates. Additionally, we examined the influence of sclerotial size on carpogenic germination. The findings revealed a significant effect of pathogen virulence on the incidence and severity of Sclerotinia stem/leaf rot and subsequent sclerotia production. Among the tested plant species, 26 exhibited heightened susceptibility to the highly aggressive S. sclerotiorum isolate, which produces larger and more numerous sclerotia in 17 species compared to the less aggressive isolate. Furthermore, a stronger positive correlation was observed between the relative lesion length of plants inoculated with the highly aggressive isolate and the sclerotia production of this isolate (rs = 0.572; p = 0.004). Moreover, we found that larger and heavier sclerotia displayed earlier and more prolific stipes and apothecia development compared to smaller ones. Significantly, the heavyweight class demonstrated the highest carpogenic germination rate (82.4 %), followed by the average (67.2 %) and lightweight classes (59.5 %). These findings underscore the imperative for further exploration of the potential risks associated with cover crops, weeds, and flower strips serving as secondary hosts of soilborne pathogens in agricultural settings.