Phylogeny, species diversity and divergence time of Diaporthe causing leaf blight on Acer palmatum in China

The genus Diaporthe (asexual synonym: Phomopsis) encompasses pathogenic, endophytic, and saprophytic species with a broad host range, where certain species can readily migrate between hosts. As pathogens, some species of Diaporthe (asexual synonym Phomopsis) can infect a variety of host plants, resulting in severe fungal diseases. However, the species occurring on Acer palmatum has never been systematically studied. In this study, a total of 251 Diaporthe isolates were obtained from the foliage of A. palmatum showing leaf blight symptoms. Phylogenetic analyses based on five loci (ITS, CAL, HIS3, TEF, and TUB), the species delimitation analysis (ABGD, bPTP, and GMYC method), and morphology revealed that the 70 representative isolates belonged to 10 known species (including Diaporthe arecae, Diaporthe biconispora, Diaporthe caryae, Diaporthe discoidispora, Diaporthe eres, D.ganjae, Diaporthe hongkongensis, Diaporthe sackstonii, Diaporthe sojae, and Diaporthe unshiuensis). Molecular clock analyses suggested that the ancestor of Diaporthe emerged in the late Eocene, with a mean stem age of 52.37 Mya (95% HPD of 50.44-54.33 Mya) and a mean crown age of 43.95 Mya (95% HPD of 36.21-51.01 Mya). Although Koch's postulates confirmed all isolates as being pathogenic, a high degree of variation in pathogenicity was observed. Such a high diversity of Diaporthe on one single host, A. palmatum, raised questions in fungal evolution, ecology, population dynamics, and phytopathology of Diaporthe for future studies. And this provides new evidence for extrapolating global fungal diversity based on the ratio of plants to fungi.