Sudden Vine Collapse May Be Associated with Combination of Virus Pathogens
October 07, 2019
|A Cabernet Sauvignon vine on Freedom rootstock in a 25 year-old Lodi vineyard displays sudden vine collapse
symptoms from collapse during the 2019 growing season. Photos: Ted Rieger
Mystery (or sudden) vine collapse, reported by winegrape growers in the Lodi AVA since 2011, and now observed in other California grapegrowing regions, may be associated with a combination of virus pathogens including leafroll virus and grapevine vitiviruses. It appears that certain rootstocks, notably Freedom, and perhaps others, are more sensitive to these virus combinations and more prone to vine collapse.
The Lodi Winegrape Commission (LWC) presented an update at an October 1 meeting on recent research on sudden vine collapse and the results of lab testing of vines from Lodi vineyards where vine collapse has occurred.
Background and Vine Collapse Symptoms
Since 2011, growers in the Lodi AVA have reported observing individual or small groups of vines on Freedom rootstock collapsing, or suddenly dying, without being able to determine a definite cause. Some growers reported 30 percent of a vineyard block collapsing within two years. By 2018, the vine collapse reached an economic threshold of destruction affecting enough growers financially (20+) to gain more attention.
Dr. Stephanie Bolton, LWC grower communications and sustainable winegrowing director, said, “At least three entire blocks were ripped out because of this and more will follow this winter. I have a growing list of approximately 30 vineyard blocks to include in our case studies from Lodi and beyond.”
Bolton listed the following symptoms of vine collapse as observed in Lodi, in a handout provided at the October 1 meeting:
- Vines may show stunted shoots around May—July, growing to less than half the size of healthy shoots.
- Many vines push out fruit and then collapse.
- Collapsed vines lack feeder roots.
- The entire vine goes from having green shoots to being completely dried up rather quickly (typically in 2-6 weeks).
- The symptoms look similar to Eutypa dieback, but vine death is more rapid and without cankers.
- In many cases, the graft union appears rotten, and when the trunk is sawed at the junction, dark, necrotic tissue is visible.
- The patch of collapse in a block can tend to spread in the direction of the wind, and in a rough circular shape, which can be seen in Google Maps once it gets large enough.
- Cases of sudden vine collapse have also been observed in vineyards in Stanislaus County, and in vineyards in the Central Coast counties of Monterey, San Luis Obispo and Santa Barbara.
Vine Sample Lab Testing Results
Dr. Maher Al Rwahnih, UC Davis (UCD) plant virologist and administrator of the Foundation Plant Services (FPS) diagnostics and research lab, presented results of lab testing for virus infections from vine samples collected from four Lodi vineyards on July 18, 2019. Rwahnih’s lab processed 24 samples using high throughput DNA sequencing to test for viruses of known agronomic significance.
Samples of both rootstock and scion tissues were collected and processed separately from three vines each in four different vineyards showing symptomatic vines. The four vineyards ranged in age from 6 years-old to 25+ years-old and included: a vineyard planted in 1993 with Cabernet Sauvignon on Freedom rootstock, a vineyard planted in 2013 with Pinot Noir on Freedom, and two different vineyards with Chardonnay on Freedom.
Symptomatic vines tested positive for grapevine leafroll-associated virus 3 (GLRaV-3) and many were also co-infected with one or more viruses from the genus Vitivirus. Five vitiviruses have been known and identified for some time, and FPS tests for these known vitiviruses: grapevine virus A (GVA), GVB, GVD, GVE, and GVF. Some of these vitiviruses are associated with rugose wood complex diseases. In grapevines they can cause corky bark, stem pitting and grooving under the bark, swelling at the graft union and stem cracking.
Al Rwahnih cited past and recent research related to virus co-infections in grapevines and their association with grapevine diseases and vine decline.
A research paper co-authored by Al Rwahnih and other UCD colleagues published in 2018 in the European journal of plant pathology, “Synergy between grapevine vitiviruses and grapevine leafroll viruses,” suggested the potential for a synergistic enhancement of grapevine disease in co-infected vines. This paper’s abstract stated: “An interactive relationship between vitiviruses and grapevine leafroll viruses was characterized in grapevine. Grapevine viruses A and B (GVA and GVB) were found more frequently in the presence of co-infecting Grapevine leafroll associated viruses (GLRaV-1, -2 or -3) than in their absence. The titers of the vitiviruses in co-infection with leafroll viruses were found to be higher than were their titers in the absence of leafroll virus infection. The occurrence of vitivirus-associated stem-pitting symptoms was correlated with leafroll virus co-infection. Specific pairing associations on the species level were found between different viti- and leafroll virus species: GVB was associated preferentially with GLRaV-2; GVA was associated preferentially with GLRaV-1 and GLRaV-3.”
Al Rwahnih also cited a recent research paper in the journal, Archives of virology, July 2019, with FPS director Dr. Deborah Golino as a co-author, that identifies and names five new vitiviruses—GVG, GVH, GVI, GVJ, and GVL.
Al Rwahnih also discussed the concept of virus-induced rootstock decline (VIRD), investigated by Golino and UCD colleagues that showed the combination of GLRaV-2 and GVB leads to severe stunting on Freedom rootstock. This work supports the hypothesis that rootstock response to virus infection depends on the rootstock genotype and the virus type. More information on this can be found in a paper co-authored by Golino available at http://iv.ucdavis.edu/files/108796.pdf
In addition, some Lodi vine samples tested positive for viroids—the smallest infectious pathogens known. Viroids are smaller than a virus, consist solely of a single strand of RNA, and can cause disease in certain plants.
Fungal Pathogen Testing
Dr. Akif Eskalen, UCD plant pathologist and UC Cooperative Extension specialist, sampled scion and rootstock tissues for fungal pathogens from the same Lodi vines collected on July 18. Testing revealed a number of fungal pathogens common in grapevines (Eutypa, Botryosphaeria, Phaeominiella and others) but no consistent single fungal pathogen was found among all vine samples.
Although grapevine trunk diseases and pathogens can contribute to vine stress, they are not known to cause the rapid decline or death of an entire vine. Based on observations to date, Eskalen said, “Grapevine trunk diseases are not the main cause of this problem.”
To date, only samples collected from vines on Freedom rootstock have gone through comprehensive lab testing. The researchers believe other rootstocks, such as Harmony, may also be susceptible to collapse. The researchers have not seen evidence of differences in susceptibility based on the scion variety.
At this time, advice to growers for managing sudden vine collapse is similar to management of leafroll viruses in general: reduce and control spread of mealybug vector populations, and reduce and eliminate virus inoculum by rogueing infected vines.
Future Research Plans
Future research on sudden vine collapse will continue to collect case studies, test vines at collapse sites to further determine the cause, elucidate risk factors, investigate possible relationships between co-infections of leafroll viruses with vitiviruses, and identify the susceptibility and resistance of specific rootstocks to collapse.
The LWC will continue to study the issue, pursue research funding, monitor vineyard sites, provide grower outreach, and develop management strategies. Growers who believe they have observed sudden vine collapse in their vineyards are encouraged to contact Dr. Bolton (firstname.lastname@example.org) to report their experiences and be added to the case study list.