Colletotrichum macroconidii sp. nov. and six new records of Colletotrichum (Glomerellaceae, Glomerellales) from southwestern China.

Colletotrichum, a genus in the phylum Ascomycota and the family Glomerellaceae, is globally recognized as a significant plant pathogen affecting various hosts. In this study, 31 Colletotrichum strains were isolated from plant hosts in southwestern China, specifically from Guizhou and Yunnan Provinces. Phylogenetic and morphological analyses revealed one novel species, Colletotrichum macroconidii sp. nov., and 11 previously known species. Six of these species represent new host and regional records: C. fioriniae, C. trichellum, C. juglandicola, C. nanhuaense, C. jiangxiense, and C. magnum, in addition to five known species: C. nymphaeae, C. metake, C. fructicola, C. siamense, and C. gloeosporioides. Multilocus phylogenetic analyses placed strains of C. jiangxiense in a well-supported clade with C. nullisetosum, C. oblongisporum, C. gracile, and C. tengchongense, which are here treated as synonyms due to their nomenclatural invalidity, morphological overlap, and phylogenetic evidence. Similarly, C. speciosum and C. simulanticitri clustered with C. nymphaeae and are synonymized with it based on insignificant genetic divergence and invalid nomenclatural status. Species identification was conducted using a comprehensive approach that combined multilocus phylogenetic analysis with detailed morphological characterization. This expanded dataset significantly contributes to our understanding of the genetic diversity and ecological distribution of Colletotrichum in southwestern China.