Identification and pathogenicity of Colletotrichum truncatum causing yam anthracnose - A new record in China

Yam (Dioscorea spp.) is a significant tuber crop. In October 2022, yam (Dioscorea opposita Thunb.) leaves exhibiting typical anthracnose symptoms were observed at the Yam Germplasm Resource Nursery of Wen County, Jiaozuo City, Henan Province, China. The disease incidence was recorded at 92.05%. The symptoms manifested as brown to dark brown circular or irregular large spots on the leaves, some of which displayed noticeable irregular concentric rings. A total of 23 isolates were obtained, with JCHN023-1 and JCHN003 isolates being the representative. The pathogen was successfully re-isolated from lesions of inoculated leaves, fulfilling Koch's postulates. Morphologically, the conidia appeared colorless, crescent-shaped, circular blunt at both ends, and measured (15.2-) 18.2-30 (-34.1) x (2.1-) 2.3-3.9 (-4.2) mu m in length (average = 24.1 x 3.1 mu m) without septa. The setae were black-brown and exhibited 1-4 septa. Subsequently, a multigene phylogenetic analysis, involving internal transcribed spacer (ITS), partial actin (ACT), chitin synthase 1 (CHS-1) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH), identified the fungus as Colletotrichum truncatum. Inoculation of detached leaves from 10 varieties of D. opposita confirmed their broad-spectrum pathogenicity to yam. This represents the first report of yam anthracnose caused by C. truncatum in China and provides a theoretical foundation for yam anthracnose prevention and control.