Abstract
Anthracnose (Colletotrichum spinaciae) and powdery mildew (Erysiphe pisi) are important diseases of common vetch (Vicia sativa) and often co-occur in the same plant. Here, we evaluate how C. spinaciae infection affects susceptibility to E. pisi, using sterilized and non-sterilized field soil to test the effect of resident soil microorganisms on the plant's immune response. Plants infected with C. spinaciae (C(+)) exhibited a respective 41.77~44.16% and 72.37~75.27% lower incidence and severity of powdery mildew than uninfected (C(-)) plants. Moreover, the net photosynthetic rate, transpiration rate, and stomatal conductance were higher in the C(-) plants than in the C(+) plants prior to infection with powdery mildew. These differences were not recorded following powdery mildew infection. Additionally, the activities of superoxide dismutase, polyphenol oxidase, and catalase were higher in the C(+) plants than in the C(-) plants. The resident soil microbiota did not affect the plant responses to both pathogens. By uncovering the mechanistic basis of plant immune response, our study informs integrated disease management in a globally important forage crop.