Taxonomy and diversity of freshwater ascomycetes fungi in Thailand and Southern China

Abstract

Lignicolous freshwater fungi are those that grow on submerged woody debris in freshwater streams, ponds, lakes, tree hollows, peat swamps and dams. They play an important role in nutrient and carbon cycling, biological diversity and ecosystem functioning of freshwater ecosystems with their ability to decompose lignocellulose in woody litter, softening the wood and releasing nutrients. Fungi in freshwater represent a phylogenetically varied Ascomycota group that may be thought of as an ecological assembly rather than a taxonomy category that reflects the presence of freshwater fungus throughout various lineages. Freshwater ascomycetes are ascomycetous fungi that have been found in freshwater habitats. We are carrying out a survey on the diversity of lignicolous freshwater fungi in Thailand and Southern China. In this study, 97 species were introduced based on phylogenetic analysis and morphological characters, of which 36 from Thailand and and 61 from China. The 97 species belong to two classes (Dothideomycetes and Sordariomycetes) of ascomycota, based on evidence from DNA sequence data and morphology, 54 new species, 37 new records, six new collections are introduced. In addition, three new combinations were introduced and molecular data of two fungal taxa were provided for the first time. Descriptions, illustrations and phylogenetic tree for these species were provided. Diaporthomycetidae is one of the seven subclasses of Sordariomycetes and contains 30 lineages that are only known from freshwater. The subclass is therefore of interest when considering the evolution of freshwater fungi. Several lineages of Diaporthomycetidae are morphologically unique and taxa cluster with strong support, but have weak support at the base of the trees. The phylogenetic and MCC trees generated in this study indicate that Aquapteridospora, Barbatosphaeriaceae, Bullimyces, Cancellidium, Ceratolenta, Conlarium, Phialemoniopsis, Pseudostanjehughesia and Rhamphoriaceae are distinct genera/families that evolved in the family/order time frame. The new orders Barbatosphaeriales (177 MYA), Cancellidiales (137 MYA), Ceratolentales (147 MYA), Conlariales (138 MYA) and Rhamphoriales (133 MYA) and six new families, Aquapteridosporaceae (110 MYA), Cancellidiaceae (137 MYA), Ceratolentaceae (81 MYA), Bullimycetaceae (81 MYA), Phialemoniopsaceae (59 MYA), and Pseudostanjehughesiaceae (111 MYA) are introduced with evidence from phylogenies, divergence estimates and distinct morphologies. Of these families, Aquapteridosporaceae, Cancellidiaceae, Bullimycetaceae, and Pseudostanjehughesiaceae are only known from freshwater. In addition, three new collections of Cancellidium from streams in China and Thailand were made and isolated them into culture, extracted DNA and carried out multigene phylogenetic analysis and divergence time estimation which placed the genus in Diaporthomycetidae. In addition, we introduce three additional species to Cancellidium. Hypocreomycetidae is a highly diverse group with species from various habitats. Species in this subclass have been reported as pathogens, endophytes, parasites, saprobes, fungicolous, lichenicolous, algicolous, coprophilous and insect fungi from aquatic and terrestrial habitats. In this study, we focused on freshwater fungi of Hypocreomycetidae which resulted 41 fresh collections from China and Thailand. Based on morphological and phylogenetic analyses, we identified 26 species belonging to two orders (Hypocreales, Microascales) and six families (Bionectriaceae, Halosphaeriaceae, Microascaceae, Nectriaceae, Sarocladiaceae and Stachybotryaceae). Ten new species, 13 new habitats and geographic records are introduced. Mariannaea superimposita, Stachybotrys chartarum and S. chlorohalonatus are recollected from freshwater habitats in China. Based on phylogenetic analysis of combined LSU, SSU, ITS, rpb2 and tef1-α sequences data, Emericellopsis is transferred to Hypocreales genera incertae sedis; Pseudoacremonium is transferred to Bionectriaceae; Sedecimiella is placed in Nectriaceae; Nautosphaeria and Tubakiella are excluded from Halosphaeriaceae and placed in Microascales genera incertae sedis; Cancellidiales and Faurelina are excluded from Hypocreomycetidae. In addition, phylogenetic analysis and divergence time estimates showed that Ascocodina, Campylospora, Cornuvesica and Xenodactylariaceae formed distinct lineages in Hypocreomycetidae and they evolved in the family/order time frame. Hence, a new order (Xenodactylariales) and three new families (Ascocodinaceae, Campylosporaceae, and Cornuvesicaceae) are introduced based on phylogenetic analysis and divergence time estimations. Ancestral character state construction performed for different habitats (freshwater, marine and terrestrial) of this subclass indicates that Hypocreomycetidae evolved from terrestrial ancestor whereas marine and freshwater fungi have been independently evolved. The results further support that early diverging clades of this subclass mostly comprises terrestrial fungi and freshwater and marine fungi have been secondarily derived while the crown clade (Nectriaceae) fairly represents all three habitats. The evolution of various morphological adaptations towards their habitual changes have also been discussed. Fungi associated with aquatic plants are poorly been studied. Few freshwater endophytes have been reported. While, there are little studies about freshwater plant pathogens. In this study, two fungal pathogens were isolated from aquatic plants of Alternanthera philoxeroides and Oryza sp. respectively. Based on phylogenetic analysis and morphological characters, the two species were identified as Curvularia sorghina and Nigrospora oryzae, the detailed descriptions and illustrations are provided for these two species.