Planting a vineyard with vines that are not infected with common grapevine viruses is essential to the bottom line. It can be challenging enough to keep over 1000 vines per acre relatively free from the normal canopy and trunk diseases such as grapevine powdery mildew and Eutypa dieback. Those diseases are caused by infections that occur naturally after vines are planted and can be controlled with proper farming practices.

It doesn't work that way with diseases caused by viruses. Farming practices can rarely mitigate the effect a virus has on fruit quality. Grapevine viruses are primarily spread by grafting - when either the rootstock or the variety grafted onto the rootstock is infected - or by vegetative propagation.  Some viruses are also spread by specific insects or nematodes which acquire a virus when they feed on a diseased vine and then transmit it to other vines by feeding. Virus diseases are not curable and once a vine is infected, it will always be diseased.

Grapevine leafroll virus is an example of a common virus that can be avoided – at least initially – by planting certified vines. It is one of the viruses that cause the leaves of red-berried varieties to turn red in the fall. (The red “fall color” seen in photos of grapevines is not a good sign.) In white-berried varieties visual symptoms are more difficult to identify because the leaves do not turn red. Leafroll disease is widespread throughout the world and prevents the normal ripening process from occurring.

Unknowingly planting vines infected with leafroll virus is possible and very damaging because the virus is spread by mealybugs and scale insects. Starting with infected vines makes a bad situation worse because the incidence of diseased vines in a block quickly increases. Growers invest significant resources to control the insect vectors of leafroll, remove diseased vines and replant with clean stock.

UC Davis Foundation Plant Services

Starting out with “clean” vines is critical. And clean in this context means not infected with grapevine viruses that are known to reduce grape yield or quality. So it is important to plant a vineyard with vines that are far less likely to be infected on the day they are planted. In reality virus-free cannot be guaranteed.

To obtain the cleanest plants possible using normal nursery production practices, most growers purchase certified vines from grapevine nurseries and the source of those vines can be traced back to Foundation Plant Services (FPS) at UC Davis.

FPS provides the Foundation vines for the California Grapevine Registration and Certification Program in the California Department of Food and Agriculture (CDFA).  Nurseries obtain cuttings of Foundation vines to start their registered increase blocks. Cuttings taken from registered vines are used to create grafted or rooted vines that are sold to growers as certified vines. CDFA regulations govern the location of registered and certified blocks, and the annual inspection and testing of vines in those blocks for the targeted viruses.

Vines are planted into Foundation Blocks at FPS only after undergoing a battery of virus tests – some of which can take two or more years - as prescribed by the CDFA regulations as well as pass other evaluations. The FPS lab continually tests for viruses in the Foundation Blocks; each vine is tested every three years. For nematode transmitted viruses, each Foundation vine is tested every two years.

Protocol 2010

Nearly 10 years ago, FPS began to develop a new Foundation Block that met newly established national standards for grapevine foundation plants in the US.  The Russell Ranch Vineyard (RRV) at UC Davis contains Foundation vines which have all been propagated using a technique called microshoot tip culture – in which a 0.19 inch (0.5 mm) or smaller slice of the growing tip of a shoot is used as the starting material for a grapevine. These vines start out in small boxes on growth media. After a vine has grown large enough for tissue to be collected and tested for viruses, it must test negative for over 30 grapevine viruses.

Why so many? Because other countries have grapevine viruses that we don't have in the US, thus creating a testing protocol that includes those viruses helps to insure they are not in US Foundation Blocks. The testing protocol used to establish the RRV is known as “Protocol 2010” and it was made possible by funding in the 2008 Farm Bill that established the National Clean Plant Network (NCPN).

National Clean Plant Network

The purpose of the NCPN is to protect plants of economic value by diagnosing for plant pathogens, curing those plants, and to protect starter plants and make them available to industry. The goal of the NCPN is to sustain national funding for clean planting stock programs of key horticultural crops. There are five Grape Clean Plant Centers and they are located at UC Davis, Florida A&M University, Missouri State University, Cornell University and Washington State University. Clean Plant Centers also exist throughout the US for fruit trees, berries, citrus, hops, sweetpotatoes and roses. UC Davis FPS is also a Clean Plant Center for fruit trees, sweetpotatoes and roses.

“The National Clean Plant Network is an association of clean plant centers, scientists, educators, state and federal regulators, large and small nurseries and growers of specialty crops that work together to ensure that plant propagation material is clean and available.”

For more information on the National Clean Plant Network, visit nationalcleanplantnetwork.org

To learn more about Foundation Plant Services at UC Davis, visit fps.ucdavis.edu