Abstract
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. In this study, we developed a method for inoculating pods in vitro by soaking in a mycelial suspension. We optimized the crucial components, including the mycelial suspension concentration (40 to 60 mg mL−1), the maturity of the sampled pods (15 days after flowering), and the post-inoculation incubation period (5 days). Application of the mycelial suspension by soaking rather than spraying improved the efficiency of inoculation and made large-scale evaluation possible. Using this method, we evaluated 589 soybean germplasm resources (275 cultivars, 233 landraces, and 81 wild accessions). We identified 25 highly resistant cultivars, 11 highly resistant landraces, but only one highly resistant wild accession. Our results will aid future research on soybean anthracnose resistance, including gene discovery, the elucidation of molecular mechanisms, and the breeding of resistant cultivars.
Highlights
Anthracnose, caused by Colletotrichum truncatum, is a major fungal disease of soybean (Glycine max (L.) Merrill) [1]
Our findings provide a foundation for the discovery of resistance genes, the elucidation of their associated molecular mechanisms, and the breeding of resistant cultivars
No significant differences were observed within the range of 30 to 50 mg mL−1 over the entire incubation period, except at 3 days post-inoculation (DPI)
Summary
Anthracnose, caused by Colletotrichum truncatum, is a major fungal disease of soybean (Glycine max (L.) Merrill) [1]. All the aboveground parts of soybean plants can be infected at any stage of development by C. truncatum. During the early stages of infection, typical distinctive symptoms of anthracnose are irregularly shaped brown blotches on cotyledons, stems, petioles, leaves, and pods, which gradually develop into dark, depressed, and irregular lesions. In the top eight soybean-producing countries (Argentina, Bolivia, Brazil, Canada, China, India, Paraguay, and the USA), grain-yield losses of 25.4 million tons have been reported, including a record 16.6 million tons in China in 2006 [7]. China is the largest producer and exporter of vegetable soybean worldwide, with a cultivated area of 1.0–1.5×107 ha and pod yields of 5.0×105 tons per year [8]. Vegetable soybean production in China is concentrated in the southeastern coastal area, where anthracnose frequently occurs because of the warm, humid climate. In Zhejiang Province, the anthracnose incidence of soybean plants is about 50% and that of soybean pods is about 30% in typical fields; in severely infected fields, the incidence can increase to >90% of soybean plants and >50% of soybean pods [9,10]
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