Special rootstocks which resist both the nematode and the virus which have been produced at the University of California, Davis, California. In France genetic engineers have modified standard rootstocks to resist GVF infection, but these are not yet available for commercial use. Forntunately, the nematode vector for GVF is not present in New York, and the disease has not been a problem to our growers. These two viruses present in many of our native and weedy plant species, and the virus can be vectored by the nematode, Xiphenema americanum which is also widely distributed in New York. Work by Dr. Dennis Gonsalves at Cornell's Geneva Plant Pathology department indicates that most commonly used New York phylloxera resistant rootstocks are almost immune from infection by the ringspot virus complex.
Resistant rootstocks have a hypersensitive reaction to the virus.
When a nematode injects the virus into root tissue, the affected cells usually die preventing infection. Apparently most Vitis vinifera varieties have a similar reaction. The worst possible case is to graft a hypersensitive scion to a susceptible rootstock. When the rootstock becomes virus infected and the virus moves upward to the graft union, the hypersensitivity causes the death of reactive scion tissue. The result is graft union necrosis and vine death.