Investigation of the Colletotrichum gloeosporioides Species Complex Causing Peach Anthracnose in South Carolina.

Colletotrichum gloeosporioides, C. acutatum, and C. truncatum are causal agents of anthracnose disease of peach in South Carolina, but more recent investigations show that C. gloeosporioides is a species complex that has not yet been investigated among peach isolates. A total of 28 Colletotrichum spp. isolates associated with peach fruit anthracnose were collected in 2012 from Chesnee (10 isolates), McBee (10 isolates), Monetta (2 isolates), and Ridge Spring (6 isolates), South Carolina. Morphological characteristics indicated that all 28 isolates belonged to the C. gloeosporioides species complex. Phylogenetic analysis of the combined calmodulin (CAL), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and ß-tubulin (TUB2) gene sequences identified two species, C. siamense and C. fructicola. Cultural characteristics such as colony growth rate, shape and size of conidia, and appressoria from representative isolates of the two species largely matched previous descriptions for C. siamense and C. fructicola. Koch's postulates for C. siamense and C. fructicola were fulfilled, confirming pathogenicity of the two species on peach. A new, two-step multiplex PCR assay was developed to facilitate differentiation of the four known Colletotrichum spp. causing anthracnose of peach in South Carolina, including C. acutatum, C. truncatum, C. siamense, and C. fructicola. The first step distinguished C. acutatum from C. truncatum and the two members of the C. gloeosporioides species complex. The second assay distinguished C. siamense from C. fructicola isolates.