New Grapevine Virus Detected in California: Grapevine Pinot Gris Virus Discussed at UCD FPS Meeting
November 13, 2015
A grapevine virus formally recognized in 2012 by Italian researchers as grapevine Pinot Gris virus (GPGV) and associated with disease symptoms in Pinot Gris/Grigio in Italy since 2003, was recently detected in California grapevines in Napa Valley.
Virus testing was performed by Agri-Analysis, a laboratory testing service company based in Davis, that tested 96 randomly selected grapevine samples that the lab already had in its possession to test for grapevine red blotch-associated virus. According to Agri-Analysis lab manager Dr. Alan Wei, seven vines tested positive for GPGV that included selections of Cabernet Sauvignon, Cabernet Franc and Chardonnay from three separate vineyards in Napa Valley. This is believed to be the first reported detection of GPGV in the U.S.
Much is still unknown about this virus, and its detection in a grapevine does not necessarily mean disease symptoms are present or will occur in the future that will affect vine health. It is one more issue for grapegrowers to be aware of when evaluating grapevine health. The major California grapevine testing labs now have, or will have, the ability to test for GPGV.
The news was announced November 10 at the annual meeting of the UC Davis Foundation Plant Services (FPS), held for the first time at the recently completed Trinchero Family Estates Building at the FPS facility in Davis. Dr. Maher Al Rwahnih, FPS project scientist, provided an update on GPGV based on information presented at the recent International Congress on Viruses of the Grapevine (ICVG) held in Ankara, Turkey in September.
Disease symptoms now associated with GPGV were first observed in vineyards in Italy’s Trentino Alto Adige region in 2003. In 2012, GPGV was introduced as a new virus. Disease symptoms include chlorotic leaf mottling, leaf stunting and deformation, delayed vine growth, stunted canes, and reductions in yields.
GPGV has now been reported in symptomatic and asymptomatic wine and table grape varieties in many countries, including: Italy, France, Greece, Turkey, Spain, Portugal, Slovenia, the Czech Republic, Slovakia, Croatia, Serbia, Montenegro, Bosnia, Macedonia, Ukraine, Romania, China, and Japan.
To date, GPGV and disease symptoms have been most associated with varieties such as Pinot Gris/Grigio, Gewurztraminer, Pinot Blanc, Pinot Noir, Tocai Friulano and Glera (used for Prosecco) in Italy. GPGV has also been detected in Merlot and Cabernet Sauvignon in other European vineyards.
Studies show that the virus, and disease symptoms, can be graft transmitted. Some studies indicate that the eriophyid mite may be a vector of GPGV, but this is not confirmed. Al Rwahnih said, “Biological and molecular assays suggest that there may be symptomatic and asymptomatic GPGV isolates.” In his summary, he also said, “The effects of the GPGV infection on grapevines are still unknown and, in most cases, the virus was reported in plants with multiple virus infections.” Other viruses found in vines with GPGV can include: grapevine rupestris stem pitting-associated virus, grapevine rupestris vein feathering virus, grapevine syrah virus 1, and grapevine yellow speckle viroid 1.
Al Rwahnih emphasized that the relationship between GPGV and disease symptoms appears to be quite complex and is not yet understood. Posing some issues for possible future research he said, “Since GPGV commonly occurs with other viruses, is it a combination of viruses, the specific isolate of the virus, the titer level of the virus, or something else that determines whether disease symptoms appear?”
FPS Material Being Screened for GPGV
FPS recently added GPGV to its routine panel of tests for viruses and diseases to monitor Foundation plant material as part of its regular testing schedule. Al Rwahnih presented test results from screening performed to date for GPGV in the FPS collection. Of 254 vines screened in the Russell Ranch 2010 Protocol vineyard, zero vines tested positive for GPGV.
In the older FPS Classic Foundation Vineyard, 1,760 vines were screened with one vine testing positive for GPGV. This vine, a selection of Touriga Nacional imported from Portugal in 1981 and planted in 2001, showed no disease symptoms or health problems. As a precaution, FPS tested 20 other vines adjacent to this vine and no virus was detected in any, and there was no indication of virus spread. Al Rwahnih said the good news is that this Touriga selection has never been distributed to growers.