Molecular data reveal high host specificity in the phylogenetically isolated genus Massaria (Ascomycota, Massariaceae)

Abstract

Molecular phylogenetic analyses of a four-gene sequence matrix (LSU, SSU, rpb2, tef1) demonstrate monophyly of the genus Massaria, which is placed as most basal lineage within Pleosporales. Data from microscopic morphology, pure cultures, and phylogenetic analyses of partial SSU-ITS-LSU rDNA and tef1 sequences revealed 17 taxa of Massaria, seven of which are described as new (M. ariae, M. aucupariae, M. campestris, M. mediterranea, M. parva, M. platanoidea, M. vindobonensis). Massarina macra is formally combined into Massaria. Synonymy of the genus Aglaospora with Massaria is confirmed, and the generic type Massaria inquinans is lecto- and epitypified. Massaria vomitoria, M. gigaspora and M. pyri, commonly considered as conspecific with M. inquinans, are shown to be distinct species. Due to homonymy, the new name M. gigantispora is introduced for M. gigaspora Fuckel. Several species are lecto- and/or epitypified. A key to all treated species is provided. Most Massaria species revealed by molecular phylogenetic analyses can be well characterised by a suite of morphological traits like ascospore shape, ascospore length and width, ascospore colour in the intact ascus vs. after ejection, size of pseudothecia, presence or absence of a black stromatic zone delimiting the pseudostroma, and staining of the substrate. Two different modes of ascospore germination were observed in pure culture, i.e. hyphal or by ejection of a naked protoplast, the former developing into hyphal colonies and the latter into meristematically growing colonies. Modes of ascospore germination and colony growth were found to be characteristic for the respective species. All species were found to be highly host-specific, disproving the wide host range given for Massaria inquinans in the literature. Biodiversity of Massaria was found to be centred on the genus Acer (seven species), where up to four species can occur on the same host species, and on Rosaceae (four species). Evidence for a hemibiotrophic life style and weak parasitism of Massaria is provided and discussed. Geographic distribution of species is reconsidered, concluding that Europe may be the centre of Massaria biodiversity.