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A Reassessment of the Species Concept in Eutypa lata, the Causal Agent of Eutypa Dieback of Grapevine

First and fourth authors: University of California-Davis, Department of Plant Pathology, One Shields Avenue, Davis 95616; and second and third authors: U.S. Department of Agriculture (USDA), Albany, Berkeley, CA and Western Regional Research Center, USDA-Agricultural Research Service, 800 Buchanan Street, Albany, Berkeley, CA

Eutypa dieback is a vascular disease of several cultivated crops and trees worldwide. The attribution of the name to the agent responsible for branch dieback is ambiguous. Pathogenicity of Eutypa sp. first was reported on apricot and the causal agent was named E. armeniacae. However, no morphological differences were reported with the previously described E. lata, and some authors considered both species synonymous. Others regarded them as distinct species on the basis of pathogenesis and molecular analysis. We further investigated the relatedness of both species by phylogenetic analyses of the internal transcribed spacer region and β-tubulin gene. These analyses included several other taxa placed in the same family (Diatrypaceae), and yielded three groups. The isolates referred to as E. lata in previous work clustered with Diatrype stigma in one group. Isolates of E. armeniacae and E. lata clustered in a second group, supporting the synonymy of these species. The third group included other Eutypa spp. supporting the polyphyletic origin of this genus. Measurements of conidia length and secondary metabolite production of isolates supported the phylogenetic analyses. Secondary metabolites appeared to be a synapomorphic character shared by several taxa including E. lata, E. armeniacae, E. laevata, and E. petrakii var. petrakii.

Additional keywords: vegetative compatibility groups, Xylariales.