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Poster: Diseases of Plants: Disease Detection & Diagnosis


Association of Grapevine rupestris stem pitting-associated virus and Grapevine Pinot gris virus in declining grapevines on Schwarzman rootstock.
H. MCCOWN (1), S. Bag (1), M. Eng (1), M. Sudarshana (2) (1) University of California, U.S.A.; (2) USDA-ARS, U.S.A.

In the fall of 2014, in Napa County, California, four-year-old grapevines of Cabernet Sauvignon (Vitis vinifera) on Schwarzmann (V. riparia X V. rupestris) rootstock were found to exhibit red canopy and vine decline. Upon examination of the woody cylinder, the rootstocks, but not the scions, had extensive stem pitting. To investigate the causal agent(s), nucleic acid extracts from affected grapevines were analyzed for viruses by RT-PCR assays. These vines tested positive for the Syrah strain of Grapevine rupestris stem pitting-associated virus (GRSPaV-Syrah) and negative for five leafroll-associated viruses, three vitiviruses, and Grapevine red blotch-associated virus. Further examination by deep sequencing of a cDNA library, prepared from the dsRNA fraction of cambial scrapings from the affected trunks, and subsequent bioinformatics analysis, revealed the presence of Grapevine Pinot gris virus (GPGV) in addition to GRSPaV-Syrah. Canopy surveys conducted in the fall of 2015 indicated that >40% (n=342) of the vines had declined. It is likely that the association of GPGV and GRSPaV may have a synergistic effect resulting in the stem pitting symptom.