Mating type markers reveal high levels of heterothallism in Leptographium sensu lato

Abstract

Species of Leptographium sensu lato (Ophiostomatales, Ascomycetes) are sap-stain fungi vectored by bark beetles (Coleoptera, Scolytinae) and some species cause or are associated with tree diseases. Sexual states have been reported for more than 30 species in this group and these have been treated in the sexual genus Grosmannia. No sexual state is known for at least 59 additional species and these reside in the genus Leptographium. The discovery of sexual states for species of Leptographium relies mainly on the presence of fruiting bodies on host tissue at the time of isolation and/or intensive laboratory mating studies, which commonly have a low levels of success. In this study, markers were developed to diagnose mating-type and to study sexual compatibility of species in Leptographium sensu lato using these markers. To achieve this objective, available mating type sequences for species of Leptographium sensu lato and Ophiostoma were obtained, aligned and used to design primers to amplify MAT genes in Grosmannia and Leptographium species. Using these primers, it was possible to amplify portions of the mating type genes for 42 species and to determine thallism, in many species for the first time. Surprisingly, the results showed that heterothallic and putatively heterothallic species are abundant (39 out of 42 species) in Leptographium sensu lato, and only three species were confirmed to be homothallic. The mating-type markers developed in this study will be useful for future studies concerning mating type and sexual compatibility of species in this genus.