Phenotyping grapevine cultivars for resistance to Eutypa dieback

Authors: TRAVADON, RENAUD - University Of California, Davis; Baumgartner, Kendra

Submitted to: Phytopathologia Mediterranea
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/31/2023
Publication Date: 9/15/2023
Citation: Travadon, R., Baumgartner, K. 2023. Phenotyping grapevine cultivars for resistance to Eutypa dieback. Phytopathologia Mediterranea. 62(2):239-253. https://doi.org/10.36253/phyto-14467.
DOI: https://doi.org/10.36253/phyto-14467

Interpretive Summary: Eutypa dieback of grapevine is a trunk disease that impacts vineyard productivity worldwide. Visibly dark-brown discoloration (wood symptoms) appear consistently in the greenhouse, after inoculation of the woody stem of potted plants with the causal fungus Eutypa lata, and so wood symptoms are a common measure of comparing resistance of different grape cultivars. Leaf symptoms also develop in the greenhouse, although because their severity does not always correspond to severity of wood symptoms, some inoculation methods may be better for more consistent comparisons of cultivars (phenotyping). We compared three such methods as possible ‘phenotyping assays’, replicated with two E. lata isolates, for comparing resistance of Vitis vinifera cultivars (‘Black Corinth’, ‘Carignane’, ‘Husseine’, ‘Merlot’, ‘Muscat Hamburg’, ‘Palomino’, ‘Peloursin’, ‘Primitivo’, ‘Thompson Seedless’): Assay 1 (leaf and woody-stem symptoms measured at 1 year post-inoculation on plants propagated from rooted, dormant cuttings), Assay 2 (green-stem symptoms measured at 4 months post-inoculation on plants propagated from rooted, green cuttings), and Assay 3 (leaf symptoms measured at 6 weeks post-inoculation on plants propagated from rooted, dormant cuttings). Leaf symptoms were also rated in a field survey (for 3 years, over 5 years) of the nine cultivars and 1,200 others, in a Vitis vinifera collection (USDA National Clonal Germplasm Repository, Davis, California). Results of Assays 1 and 2 were more consistent with each other, especially with respect to the most resistant cultivars [‘Merlot’ and ‘Primitivo’ (aka ‘Zinfandel’)]’, than they were with those of Assay 3. Compared to resistant cultivars, there was more variation in what was the most susceptible cultivar, including ‘Black Corinth’, ‘Carignane’, ‘Husseine’, and ‘Thompson Seedless’, among assays and between isolates. From the field survey, leaf symptoms were present in at least one study year on 122 accessions, including ‘Husseine’, ‘Muscat Hamburg’, and ‘Thompson Seedless’. A repeatable phenotyping assay is critical for future genetic studies, to hopefully identify genes associated with resistance to this important disease, and then to use detection of such genes as molecular markers.

Technical Abstract: Eutypa dieback of grapevine is a trunk disease that impacts vineyard productivity worldwide. Wood symptoms develop consistently in the greenhouse, after inoculation of the woody stem of potted plants with the causal fungus Eutypa lata, and so wood symptoms are a common measure of host resistance/fungal virulence. Leaf symptoms also develop in the greenhouse, although reports of low correlation between severity of wood and leaf symptoms (for some cultivars and isolates) suggest that some inoculation methods are more robust than others for phenotyping cultivars for resistance. We compared three such methods as putative ‘phenotyping assays’, replicated with two E. lata isolates, for quantifying resistance of Vitis vinifera (‘Black Corinth’, ‘Carignane’, ‘Husseine’, ‘Merlot’, ‘Muscat Hamburg’, ‘Palomino’, ‘Peloursin’, ‘Primitivo’, and ‘Thompson Seedless’): Assay 1 (leaf and woody-stem symptoms measured at 1 year post-inoculation on plants propagated from rooted, dormant cuttings), Assay 2 (green-stem symptoms measured at 4 months post-inoculation on plants propagated from rooted, green cuttings), and Assay 3 (leaf symptoms measured at 6 weeks post-inoculation on plants propagated from rooted, dormant cuttings). Leaf symptoms were also rated in a field survey (for 3 years, over 5 years) of the nine cultivars and 1,200 others, in a Vitis vinifera collection (USDA National Clonal Germplasm Repository, Davis, California). Results of Assays 1 and 2 were more consistent with each other, especially with respect to the most resistant cultivars [‘Merlot’ and ‘Primitivo’ (aka ‘Zinfandel’)]’, than they were with those of Assay 3. Compared to resistant cultivars, there was more variation in what was the most susceptible cultivar, including ‘Black Corinth’, ‘Carignane’, ‘Husseine’, and ‘Thompson Seedless’, among assays and between isolates. From the field survey, leaf symptoms were present in at least one study year on 122 accessions, including ‘Husseine’, ‘Muscat Hamburg’, and ‘Thompson Seedless’. A repeatable phenotyping assay is critical for future association-genetics studies, which may identify genomic regions associated with resistance to this important disease.