Colletotrichum (Sordariomycetes, Glomerellaceae) species associated with Citrus in Guangdong Province, China

Colletotrichum species have diverse lifestyles, which can change from endophytic to pathogenic and other lifestyles such as saprobic. However, the exact mechanism of lifestyle changes is unknown. Over 20 Colletotrichum species cause citrus anthracnose worldwide and are also associated with the various Citrus species as endophytes in leaves, shoots, and fruits. The objective of this study was to explore the endophytic diversity associated with four species (Citrus reticulata, Citrus tachibana, Citrus nobilis Lour. Gonggan, and Citrus maxima (Burm.) Merr. cv. Shatian Yu) in Guangdong Province. This study collected 96 leaf and immature fruit samples from four Citrus species. In total, 183 Colletotrichum isolates were obtained, and based on multigene phylogenetic analysis of ITS, act, chs-1, gapdh and tub2 with morphology, nine known species viz. C. citricola, C. fructicola, C. gigasporum, C. gloeosporioides, C. karsti, C. plurivorum, C. siamense, C. tropicicola, and C. truncatum were identified. Herein, we report seven new hosts and six new geographical records. Among these, C. karsti and C. gloeosporioides are the most isolated species. Based on the diversity data analysis, C. gloeosporioides shows more than 0.5 haplotype diversity in the act, chs-1, ITS, and combined data sets. However, C. karsti showed a low haplotype diversity (Hd < 0.5) for single gene regions (ITS, act, chs-1, gapdh and tub2) and combined analysis (ITS + act + chs-1 + gapdh + tub2). Six Colletotrichum species were isolated from Citrus maxima and Citrus nobilis, respectively, five Colletotrichum species were isolated from Citrus tachibana, and three Colletotrichum species were isolated from Citrus reticulata. Our study reflects the rich Colletotrichum diversity associated with Citrus species in China. Furthermore, we emphasise that it is necessary to understand the intra-species diversity of Colletotrichum taxa while introducing new species in the future.