LAUSR

Colletotrichum leaf disease (CLD), mainly caused by the Colletotrichum gloeosporioides species complex (CGSC), is a serious disease of rubber tree in most rubber-growing countries. Few fungicides are available for rubber farmers to manage this disease. To control CLD effectively, it is important to test the baseline sensitivity and efficacy of fungicides against CGSC isolates. Penthiopyrad is a new succinate dehydrogenase inhibitor (SDHI) that has been registered for use in many countries. In this study, baseline sensitivity to penthiopyrad was established by mycelial growth methods using 91 CGSC isolates collected from rubber trees in China. The EC50 values of penthiopyrad ranged from 0.243 to 3.377 mg/L with a mean EC50 value of 1.685 mg/L. Penthiopyrad greatly decreased the mycelial biomass and increased cell membrane permeability of CGSC isolates. The mycelia were severely distorted, and the number of top branches increased with penthiopyrad treatment. Penthiopyrad inhibited succinate dehydrogenase activity, causing a decrease in the ATP content of CGSC isolates, and significantly inhibited conidia germination and appressorium formation on rubber tree leaves. The protective and curative efficacy of 100 mg/L penthiopyrad reached up to 98.53% and 66.79% against CLD, respectively. Our results demonstrated the high inhibitory activity of penthiopyrad against CGSC isolates and its potential for CLD management on rubber tree.