Colletotrichum species causing anthracnose disease of Carya illinoinensis in China

Anthracnose fruit rot and leaf blight caused by Colletotrichum species, are significant diseases affecting pecan in the subtropical regions of China. From 2018 to 2021, disease surveys were conducted in the provinces of Zhejiang, Anhui, Shandong, Yunnan, Jiangsu, Sichuan, Jiangxi, and Guangxi, leading to the isolation of 108 Colletotrichum isolates from symptomatic samples. Species identification was performed through multigene phylogenetic analysis of the ITS, ACT, CAL, GAPDH, TUB2, and CHS-1 DNA regions. The isolates were classified within the C. gloeosporioides, C. acutatum, C. gigasporum, and C. orchidearum species complexes, with over 52% belonging to the C. gloeosporioides complex. Twelve Colletotrichum species were identified: C. fructicola (n=48), C. fioriniae (n=18), C. siamense (n=15), C. gloeosporioides (n=5), C. nymphaeae (n=5), C. aenigma (n=4), C. jiangxiense (n=4), C. henanense (n=2), C. gigasporum (n=2), C. conoides (n=1), C. sojae (n=1), and C. cliviicola (n=1). Pathogenicity tests via point inoculations confirmed that C. fioriniae, C. fructicola, and C. siamense showed higher virulence. In wound inoculation assays, leaves inoculated with C. fioriniae, C. conoides, C. fructicola, C. siamense, and Colletotrichum sp. developed larger lesions (diameters ranging from 4.0 to 8.3 mm) compared to those inoculated with C. gigasporum, C. jiangxiense, C. sojae, C. nymphaeae, C. cliviicola, and C. henanense (lesion diameters from 2.0 to 2.5 mm). The prevalence and diversity of Colletotrichum species associated with pecan anthracnose varied among the eight provinces, with relatively greater diversity observed in Yunnan, Jiangsu, Zhejiang, and Anhui. C. fructicola (50.3 %) was the most prevalent species across most pecan-growing regions studied in China, followed by C. fioriniae (15.5 %). This study provides the first report of C. conoides, C. aenigma, C. henanense, C. jiangxiense, C. gigasporum, C. sojae, and C. cliviicola infecting Carya illinoinensis in China.