Pathogenicity of the genus Colletotrichum from fruit rot and healthy flowers in Nagasaki prefecture, Japan and identification of C. nagasakiense sp. nov.

Abstract Colletotrichum is the second most common pathogen that causes loquat fruit rot in Nagasaki prefecture, Japan. To clarify the anthracnose disease cycle in loquat trees, pathogens were isolated from collected asymptomatic flowers and rotten fruits. The isolates were identified at the species level based on morphological and molecular phylogenetic analyses. Nineteen isolates were obtained from 148 collected rotten fruits. The isolates were identified as C. fioriniae (12 isolates), C. nymphaeae (2 isolates), C. gloeosporioides (1 isolate), and four unidentified species. From 900 asymptomatic flowers, C. fioriniae (5 isolates), C. gloeosporioides (1 isolate), C. siamense (2 isolates), an unknown species (11 isolates) belonging to the acutatum species complex, and 2 were unidentified. All isolates exhibited pathogenic reactions to leaves and fruits. These results imply that C. fioriniae and C. gloeosporioides infect flowers and cause loquat fruit rot after maturation. However, those in other species remain unclear. We were unable to prove the reason for the differences in the composition of species in fruits and flowers and their proportions in this study. An isolate obtained from asymptomatic flowers that also cause anthracnose disease in loquat was identified as a novel species of Colletotrichum, and was named C. nagasakiense sp. nov.