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Title: CHARACTERIZATION OF PHOMOPSIS SPP. INFECTING GRAPES IN THE MIDWESTERN AND NORTHEASTERN US

Author
item Erincik, O
item Castlebury, Lisa
item Schilder, A M C
item Rossman, Amy
item Ellis, M

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/14/2005
Publication Date: 6/20/2005
Citation: Erincik, O., Castlebury, L.A., Schilder, A., Rossman, A.Y., Ellis, M.A. 2005. Characterization of Phomopsis spp. infecting grapesvines in the Great Lakes region of North America. Plant Disease 89:755-762.

Interpretive Summary: Phomopsis viticola is the causal agent of Phomopsis cane and leaf spot in grapes causing moderate to severe yield losses in the midwestern and northeastern US. The variability in genetics, morphology, and pathogenicity among isolates of Phomopsis on grapes in this region is not known. In this research eighty isolates of Phomopsis on grapes were obtained and evaluated. Based on molecular sequence data all but two of the isolates were determined to be P. viticola. Among the subset tested, there was considerable variability in their virulence on different plant tissues. Virulence on fruit and rachises, but not leaves and canes, was positively correlated with rate of mycelial growth. Two other species of Phomopsis were isolated from grape but neither of these were pathogenic to that host. This research will be used by plant scientists breeding new varieties of grapes that are resistant to Phomopsis cane and leaf spot disease.

Technical Abstract: Eighty isolates of Phomopsis were isolated from grapes (Vitis spp.) primarily from the northeastern United States. Isolates were grouped on the basis of DNA sequences from intron regions in the translation elongation factor 1- a and calmodulin genes. According to DNA sequencing and by comparison with the type isolate, all isolates except for two were determined to be P. viticola. Thirty representative isolates were evaluated for morphological characters and for pathogenicity on grapevine (Vitis interspecific hybrid 'Seyval') leaves and canes, and 13 of these isolates were also evaluated for pathogenicity on fruit and rachises. All isolates of P. viticola caused disease on grape. However, they differed in virulence on the different grape tissues. Some isolates that were not virulent on leaves were highly virulent on fruit and rachises. Others that were highly virulent on leaves and internodes were less or not virulent on fruit and rachises. Virulence on fruit and rachises, but not leaves and canes, was positively correlated with rate of mycelial growth of the selected isolates. These data demonstrate some specialization with respect to host tissues; however, differences are mostly of a quantitative nature, which makes it difficult if not impossible to assign biotypes. For the two isolates that did not group with a P. viticola reference strain, the internal transcribed spacer regions of the nuclear ribosomal DNA were sequenced for identification purposes. Based on the best match available in GenBank, one isolate was determined to be close to Diaporthe phaseolorum while the other isolate was Phomopsis eucommicola, a tentative species. Both isolates had significantly higher mycelial growth rates and smaller conidia than the P. viticola isolates. Neither of these species have been previously reported on Vitis. These non-P. viticola isolates were only slightly or not pathogenic to Vitis.