Virus Effects on Fruit and Wine Quality of Cabernet Sauvignon on Six Rootstocks

The objective of this project is to evaluate vine growth, fruit and wine quality of Cabernet Sauvignon when grafted onto six rootstocks with and without viruses. The trial vineyard was established at the UC Oakville Station in Napa Valley, California. Rootstocks include: Couderc 3309, Kober 5BB, Paulsen 1103, Richter 110, Millardet et de Grasset 101-14, and Rupestris St. George. Viruses include: Grapevine leafroll viruses (GLRVs), corky bark associated virus{Grapevine virus B (GVB)}, Grapevine fleck virus (GFkV), and Rupestris stem pitting virus (RSPaV), in single and mixed infections.

This year was the first year in which fruit yield and pruning weight data was collected. Three vines from each replication were measured for a total of 15 vines from each treatment. Parameters measured on fruit were: Fruit yield, cluster number per vine; berry wt (average from a 100?berry sample); fruit maturity indices (Brix, TA, and pH) per?rep; brix will be measured with a refractometer, TA by means of titration with a NaOH standard, and pH by pH meter. The cluster weight and berries per cluster yield components were calculated. Wine was not made because the vines are not fully mature.

Vine size was highly dependent on the rootstock/virus combination. In general, healthy vines were larger than virus-infected vines. At the third leaf stage, summer, 2004, all vines in the healthy treatments in all six rootstocks were rated either medium or large. In contrast, at least 45%of the vines in each virus treatment were rated small on at least one of the six rootstocks. By the 4th leaf in the fall of 2005, healthy vines were still generally larger than leafroll-infected vines; but healthy and RSP-infected vines were similar in size.

On 1103P and St. George, the two rootstocks that had no significant difference in vine growth, there was also no significant difference between healthy and virus-infected treatments in fruit yield. Yield ranged from 1.73 +- 0.29 to 2.03+-0.35 kg/vine for 11093P. On St. George yield ranged from 1.18 to1.52 kg/vine. Yield was significantly reduced in all virus treatments in 110R, although vine size was not reduced as measured by pruning weight. In Kober 5BB, the LR109 treatment yield was extremely low (0.5 kg/vine) but there was no significant difference between other virus treatments and healthy (2.2, 2.1, and 2.1 kg/vine for healthy, LR101, and RSP115, respectively).

As expected, sugar measurement (degrees Brix) was the one parameter in which there was a consistent significant reduction between the two leafroll virus-infected as compared to healthy in all six rootstocks. Treatment LR109 consistently reduced sugars more than LR101. RSP115 had no affect on sugars in 4 rootstocks and slight reduction in St. George and 3309C.