Submitted to: Mycological Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2006
Publication Date: 12/11/2006
Citation: Green, S., Castlebury, L.A. 2006. Connection of Gnomonia Intermedia to Discula Betulina and its relationship to other taxa in the Gnomoniaceae. Mycological Research. 111:62-69. Interpretive Summary: Fungi cause serious diseases of hardwood trees throughout the world. An asexual or clonal fungus causes a disease of birch trees in the summer and fall while the sexual state of a fungus occurs on birch leaves in the spring. In this study, it was discovered that these two seemingly different fungi actually represent two states in the life cycle of the same fungus. This paper also shows that that the spores from either state can cause disease. Using DNA sequence data the fungus on birch trees in Europe was determined to be related to a fungus causing a disease on butternut trees in North America. This information will be used by forest pathologists and horticulturalists who need to identify fungi causing diseases of birch trees.
Technical Abstract: Discula betulina is a foliar pathogen on birch (Betula) and Gnomonia intermedia is found on overwintered birch leaves. Perithecia of G. intermedia developed in vitro on colonies of D. betulina isolated from birch tissues in late summer, and single ascospores of G. intermedia consistently developed into colonies similar to D. betulina, producing typical D. betulina conidia. Isolates of D. betulina could be grouped into two mating types, which produced fertile perithecia of G. intermedia when mated with each other. Mycelia from single-ascospore and single-conidial isolates were inoculated onto shoots of downy birch, causing lesions and die-back from which D. betulina was consistently isolated. Internal transcribed spacer region ribosomal DNA sequence analysis confirmed the results of the morphological and mating studies and found that the closest known relatives of G. intermedia/D. betulina are Gnomoniella nana and Sirococcus clavigignenti-juglandacearum. The conclusion from these studies is that D. betulina is the anamorph of G. intermedia.