First report of Colletotrichum spaethianum causing anthracnose disease on Bletilla striata

Abstract Bletilla striata is a traditional Chinese medicine plant. Guizhou Province is the largest producer of B. striata, with the biggest cultivation area and highest yield in China. Anthracnose is the main disease affecting the crop. In July 2021, an anthracnose outbreak occurred in Shibing County, Guizhou Province, seriously affecting the yield and quality of B. striata. Thirty samples of B. striata anthracnose were collected from Shuangjing, Niudachang, and Yangliutang towns in three main planting areas of Shibing County to clarify the causal agent of B. striata anthracnose. Fifty anthracnose strains were isolated by tissue isolation and single-conidium culture. Through morphological observation and multigene phylogenetic analysis of the internal transcribed spacer, actin, beta-tubulin, glyceraldehyde-3-phosphate dehydrogenase and chitin synthase genes, the isolated strains were identified as Colletotrichum spaethianum. The infection process of C. spaethianum on B. striata leaves was observed by cell tissue staining. The results showed that at 25°C, the conidia of C. spaethianum on B. striata leaves began to germinate after 3 h, and the peak period of conidia germination was 8 h. Appressoria formation peaked after 24 h. During 48–72 h, the hyphae randomly expanded horizontally and vertically on the host surface, gradually forming a reticular distribution. This study is the first report of C. spaethianum causing anthracnose in B. striata. Our study clarifies the infection and development process of C. spaethianum on B. striata leaves, thus providing a theoretical basis for further study on the monitoring of B. striata anthracnose.