What are the common anthracnose pathogens of tropical fruits?
Species of Colletotrichum are associated with anthracnose of a wide range of host plants including cultivated and wild tropical fruits. The genetic and ecological diversity of species associated with wild fruits are poorly explored, as compared to those associated with pre and postharvest diseases of cultivated fruits. In the present study, isolates of Colletotrichum were obtained from commercially available cultivated fruits, wild fruits (from native trees in natural habitats) and a few herbaceous hosts collected in northern Thailand. These isolates were initially characterized based on analysis of complete sequences of nuclear ribosomal internal transcribed spacer (ITS), into the genetically defined species complexes of Colletotrichum gloeosporioides, C. acutatum, C. boninense and C. truncatum. The isolates were primarily identified in the C. gloeosporioides species complex, based on a strongly supported clade within the ITS gene tree and were further characterized using multi-gene phylogenetic analyses and morphology. Phylogenetic analyses of ITS, partial sequences of actin (ACT), calmodulin (CAL), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), glutamine synthetase (GS) and β-tubulin (TUB2) genetic markers were performed individually and in combination. Colletotrichum gloeosporioides sensu stricto was identified from lime (Citrus aurantifolia) and rose apple (Syzygium samarangense). Colletotrichum fructicola was isolated from dragon fruit (Hylocerous undatus) and jujube (Ziziphus sp.). Colletotrichum endophytica was found only from an unknown wild fruit. We observed a considerable genetic and host diversity of species occurring on tropical fruits within the clade previously known as Colletotrichum siamense sensu lato. The clade consists of isolates identified as pre and postharvest pathogens on a wide range of fruits, including coffee (Coffea arabica), custard apple (Annona reticulata), Cerbera sp., figs (Ficus racemosa) mango (Mangifera indica), neem (Azadirachta indica) and papaya (Carica papaya) and was the dominant group of species among most wild fruits studied. With the exception of one isolate from banana, which grouped in the C. siamense clade, all the other isolates were identified as Colletotrichum musae. A new species, Colletotrichum syzygicola, associated with Syzygium samarangense in Thailand, is introduced with descriptions and illustrations. This study highlights the need to re-assess the evolutionary relationships of Colletotrichum species occurring on cultivated and wild fruits with emphasis on their ecology and cryptic diversification including sampling at regional and global scales.