Species diversity of <i>Diaporthe</i> on mangroves: Taxonomic novelties, pathogenic associations, and phylogenetic reassessment of endophytes

<i>Diaporthe</i> species are frequently reported as endophytes on mangroves. These species are also known pathogens affecting several important hosts worldwide, but have yet to be explored as pathogens in mangrove environments. In this study, symptomatic leaves and stems of several mangrove species were collected from mangrove forests and estuaries in Thailand. Forty-five <i>Diaporthe</i> strains were isolated from symptomatic leaves and stems of various mangrove species, associated with leaf spots and stem cankers, respectively. A polyphasic identification approach, comprising morphological, multilocus phylogenetic analyses (ITS, <i>TEF1-α</i>, <i>TUB2, CAL</i>, and <i>HIS3</i>), and pairwise homoplasy index tests, identified two new species complexes, 10 <i>Diaporthe</i> species belonging to three sections (Eres, Foeniculina, and Sojae). This included <i>D. mayteni</i> species complex, <i>D. tanakae</i> species complex, three novel species: <i>Diaporthe mangroviorum, D. narathiwatensis</i>, and <i>D. rhizophoracearum</i>, as well as 19 new host-pathogen associations for <i>D. arecae, D. azadirachtae, D. biconispora, D. charlesworthii, D. siamensis, D. ueckeri</i>, and <i>D. vitimegaspora</i>, and two new geographic records for <i>D. azadirachtae</i> and <i>D. charlesworthii</i>. Pathogenicity was confirmed on their original mangrove hosts using detached leaf assays, showing varying levels of pathogenicity. We also present evidence supporting synonymizing of <i>D. eleutharrhenae, D. pseudobauhiniae, D. xishuangbannaensis</i>, and <i>D. yunnanensis</i> with <i>D. vitimegaspora</i>. Furthermore, the taxonomic placement and identity of previously reported mangrove endophytic <i>Diaporthe</i> species have been updated. Based on this and previous studies, a total of 93 strains belonging to 16 <i>Diaporthe</i> species are associated with mangrove species. The findings of this study gave us a more holistic understanding of the <i>Diaporthe</i> species associated with mangroves, their lifestyles, etiology, and host range.