Polyphasic identification of two novel Colletotrichum species causing leaf spots on mangroves in Thailand

Mangroves play a significant part in the marine ecosystem and harbour a plethora of microorganisms vital for various ecological functions. However, they remain vulnerable to disruptive impacts caused by fungal plant pathogens. In this study, leaves with anthracnose symptoms were collected from mangrove forests in Prachuap Khiri Khan, Thailand. Three species were identified using a polyphasic approach namely two new species – Colletotrichum avicenniae from Avicennia marina, Colletotrichum lumnitzerae from Lumnitzera racemosa, and a known species Colletotrichum tropicale. Combined analysis of ITS, gapdh, chs-1, act, and tub2 sequence data coupled with Genealogical Concordance Phylogenetic Species Recognition Analysis (GCPSRA) supported the two strains as two distinct species within the gloeosporioides species complex. The three Colletotrichum species were compared and differentiated with closely related taxa. Koch’s postulates were proven, demonstrating that C. avicenniae, C. lumnitzerae, and C. tropicale cause anthracnose leaf spots in mangroves. Understanding the classification and etiology of these fungal pathogens will contribute to a more comprehensive knowledge of mangrove biology within the marine ecosystem.