The Effect of Grapevine Latent Viruses on Non-AXR Rootstocks

1994 Final Report – Severe latent virus symptoms have been observed in new vineyards planted to non-AXR rootstocks throughout the state. The symptoms may include severe stunting, internode shortening, leaf discoloration, leaf rolling, stem pitting, disorders of the graft union and death. It is suspected that growers have empirically selected scion materials that have included virus strains which cause only mild symptoms on AXR-1. When these scions are grafted to certified rootstocks, the latent virus symptoms appear. Furthermore, Central Valley field selections which have been propagated on their own roots also seem to be affected. Twenty-six samples were collected from affected vineyards throughout the state during 1992-1993, propagated and planted in the Davis Grapevine Virus Collection, and ELISA tested for eight viruses including grapevine corky bark-associated virus (GCBaV), grapevine leafroll-associated viruses (GLRaV) types I,II, III, and IV, grapevine virus A (GVA), grapevine fanleaf virus (GFLV) and tomato ringspot virus (TmRSV). GCBaV isolate 100 was detected in an unusually large number of samples; 13 of 2 6 tested strongly positive. GLRaV II was detected in 4 of 26 samples. Two samples were positive for GLRaV III, which is considered to be the most common leaf roll type in California. Two selections tested positive for GVA; one selection tested positive for GFLV; and one selection tested positive for GLRaV I. Seven samples tested positive for more than one virus. No samples tested positive for GLRaV IV or TmRSV. Woody indexing and in vitro grafting is in progress. Five additional samples were collected in winter 1993-1994 and are being propagated.