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Association of Grapevine rupestris stem pitting-associated virus in declining Cabernet Sauvignon grapevines grafted on Schwarzmann in California
T. L. LAWLER (1), A. Rowhani (1), J. K. Uyemoto (2), M. R. Sudarshana (2). (1) UC Davis, Davis, CA, U.S.A.; (2) USDA-ARS, Davis, CA, U.S.A.

In fall 2014 in Napa County, California, four year old grapevines of Cabernet Sauvignon (CS) (<i>Vitis vinifera</i>) on Schwarzmann (<i>V. riparia </i>X (<i>V. rupestris</i>) rootstock, were found to exhibit red canopy and vine decline.  Disease incidence was 15.2% (n=342).  Several affected and healthy vines were uprooted and trunk sections, comprised of scion and rootstock, were excised and brought back to the laboratory.  The trunk specimens were autoclaved briefly and bark removed to expose the woody cylinder.  The rootstocks, but not scions, exhibited extensive stem pitting symptoms.  Nucleic acid extracts were prepared from petioles and tested by RT-PCR or PCR.  Affected grapevines tested negative for eight leaf roll-associated viruses, four vitiviruses and Grapevine red blotch-associated virus.  Affected, but not healthy, vine samples tested positive for the Syrah strain of <i>Grapevine rupestris stem pitting-associated virus</i> (GRSPaV).  Analysis of the nucleotide sequence of the RT-PCR products indicated that the GRSPaV isolate was 92% identical to GRSPaV Syrah strain in California and 98% identical to a GRSPaV isolate in Australia.  The latter strain was detected in Syrah grapevines grafted on 1103 Paulsen (<i>V. berlandieri</i> X <i>V. rupestris</i>) that exhibited symptoms of red canopy, swollen graft union and stem pitting.  This is the first reported incidence of GRSPaV associated with declining CS grapevines on Schwarzmann rootstock.

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