Abstract
Background: Anthracnose caused by Colletotrichum truncatum is a major fungal disease of soybean, especially vegetable soybean (edamame). Studies of this disease have mainly focused on resistance evaluation, but the primary methods used—in vivo inoculation of pods or plants under greenhouse or field conditions—have limitations with respect to accuracy, stability, scale, and environmental safety. Result: In this study, we developed a method for inoculating pods in vitro that entails soaking in a mycelial suspension. We optimized the crucial components, including the mycelial suspension concentration (40 to 60 mg mL-1), maturity of sampled pods (15 days after flowering), and post-inoculation incubation period (5 days). Application of the mycelial suspension by spraying rather than soaking improved the efficiency of inoculation and made large-scale evaluation possible. Using this method, we evaluated 589 soybean germplasm resources [275 cultivars (C), 233 landraces (L), and 81 wild-type accessions (W)]. This screening resulted 37 highly resistant (25 C, 11 L, and 1 W), 148 resistant (100 C, 43 L, and 5 W), 210 moderately susceptible (116 C, 77 L, and 17 W), 91 susceptible (23 C, 52 L, and 16 W), and 103 highly susceptible (11 C, 50 L, and 42 W) materials. Conclusions: The resistance levels of soybean germplasm resources were effectively distinguished by the method we developed. We thus identified many resistant cultivars but only a few resistant landraces and wild-type germplasm resources. Our results will greatly aid future research on soybean anthracnose resistance, including gene discovery, elucidation of molecular mechanisms, and the breeding of resistant cultivars.