The Effect of Grapevine Latent Viruses on Alternative Rootstocks
1993 Final Report – An epidemic of latent virus disease is suspected in new vineyards planted to alternative rootstocks throughout the state. The working hypothesis which explains this observation is that growers have been propagating scion materials selected empirically for virus strains which cause mild symptoms on AXR-1. This hypothesis is supported by widespread observations of severe latent virus symptoms in Northcoast vineyards where field scion selections, which appear healthy on AXR-1, have been grafted to certified alternative rootstocks. Furthermore, Central Valley field selections which have been propagated on their own roots also seem to be affected. Symptoms include severe stunting, internode shortening,leaf discoloration, leaf rolling, abnormal dormancy, shoot tip necrosis, severe pitting and grooving at the graft union, dead tissue at the graft union, discoloration of the rootstock wood, and death 2 to 3 years after planting. The hypothesis that latent viruses are causing these vineyard failures needs to be tested immediately. We propose to do this by field budding latent virus infected scions to a panel of alternative rootstocks and observing the effects. The effect on bench grafts will also be studied. In addition, survey work needs to be conducted as soon as possible to obtain information on the impact of this problem in the nursery and in the vineyard. If this epidemic is severe, faster virus detection techniques will be needed to screen field scion selections. In addition, many California clonal materials which are not certified may need to be treated for virus infection. Last year, 2 5 sites where vineyard replant failure may have been caused by the presence of latent viruses were selected for further work. Wood was collected from vines in those sites and propagated. Observations thus far show that the samples have poor vigor and show many characteristic virus symptoms. ELISA testing and green-grafting, using a mini-chip graft developed by Golino, is in progress. Results are pending. A history of affected vineyards was started and shows that the most severe problems are on 3 3 09 and Freedom. However, this may be coincidental and is still a preliminary finding.