Phylogenetic diversity of Colletotrichum species (Sordariomycetes, Glomerellales, Glomerellaceae) associated with plant diseases in Thailand

Colletotrichum is a cosmopolitan fungal genus, and its species are known for their important role as plant pathogens. They also occur as endophytes and saprobes. The genus comprises species complexes, many of which include cryptic species that are morphologically similar but phylogenetically distinct.

Colletotrichum is characterized by globose to subglobose ascomata and acervular conidiomata and hyaline, aseptate ascospores and conidia, although a few species produce septate ascospores. Ascospores are typically cylindrical, oval, or fusiform, while conidia are mostly ellipsoidal to ovoid. Many Colletotrichum species also produce appressoria, which are formed at the tips of germ tubes or directly from the mycelium.

In this study, we collected diseased leaves and pods with spots, blight, and blotches from Chiang Mai, Chiang Rai, and Tak provinces in Thailand. For species identification and delimitation, we employed a biphasic approach incorporating morphological data and multigene phylogenetic analyses of the locus of the internal transcribed spacer (ITS, nuclear rDNA consisting of ITS 1-5.8 S-ITS 2) and the genes encoding for glyceraldehyde- 3 - phosphate dehydrogenase (GAPDH), chitin synthase 1 (CHS 1), actin (ACT), beta-tubulin 2 (TUB 2), histone (H 3), and calmodulin (CAM).

We obtained 20 Colletotrichum isolates representing eight species, among which we propose two new species: Colletotrichum dendrobii (from Dendrobium sp.) and C. musichiangmaiense (from Musa sp.). We also establish 13 new host records (for six species): C. castaneae (on Jasminum grandiflorum), C. chrysophilum (on Terminalia sp.), C. endophyticum (on Artocarpus heterophyllus, Begonia luxurians, Cassia sp., Castanopsis sp., Ficus auriculata, and Schefflera sp.), C. fructicola (on Castanea sp., Hedychium sp., and Rhododendron sp.), C. jiangxiense (on Artocarpus sp.), and C. schimae (on Jasminum sp.).

In addition, this is the first study to present the sexual morph of C. endophyticum.