Molecular phylogeny of dogwood anthracnose fungus (Discula destructiva) and the Diaporthales

Abstract

Dogwood anthracnose, caused by Discula destructiva Redlin (1991), is a disease of several native dogwood species in North America. A teleomorph has not been found since the first reports of this disease in the 1970s, although the conidial state suggested a relationship to diaporthalean species. Phylogenetic analyses based on nuclear small subunit rDNA sequences of 47 perithecial ascomycetes placed D. destructiva into the Diaporthales with high bootstrap support. A phylogeny of 20 diaporthalean species based on large subunit rDNA inferred three major clades in the Diaporthales. Discula destructiva and four other Discula species formed a clade with Plagiostoma euphorbiae, Gnomonia padicola, G. setacea, Pleuroceras pleurostylum, Linospora capreae, Amphipor-the castanea, Apioplagiostoma aceriferum, Melanconis marginalis, and Apiosporopsis carpinea. Its sister group included Cryphonectria parasitica, Cryptodiaporthe corni, Endothia eugeniae, Valsa ambiens subspecies leucostomoides, and Apiognomonia supraseptata. Diaporthe phaseolorum formed a distinct basal branch. A primer pair (RPB2-P2F and RPB2-P3R) was developed to amplify a part of the gene encoding the second largest subunit of RNA polymerase II (RPB2) based on published pyrenomycete sequences. The RPB2 phylogeny supported the close relationship of D. destructiva and the diaporthalean species. Characters of pigmentation and anamorph agree with the phylogeny to some extent and emphasize the importance of anamorphs and pigmentation in the taxonomy of the Diaporthales. Family concepts based on perithecium position, ascus persistence, and ascospore morphology were rejected, and a new phylogenetic classification is needed.