Characterization of Grapevine Latent Viruses

Work on this project is aimed at three primary objectives: 1) to determine which virus or combination of viruses is responsible for these vineyard failures; 2) to test rootstock selections to determine their relative susceptibility to latent viruses; and 3) to apply new molecular tests to our characterized latent virus selections in hope of developing reliable, fast lab procedures to screen field selections. At the end of our first year of funding, we have made good progress in each area. Testing of latent virus isolates from field selected sites is progressing and useful information is accumulating. Evidence continues to suggest that the CB-100 ELISA test (which reacts with the leafroll isolate now known as French GLRaV-2) is useful in predicting latent virus problems. We have also established that the disease Kober stem grooving (KSG) occurs in the United States and that the ELISA test for GVA seems to detect the causal agent. We are working to optimize both these tests. Grafting experiments with various selected rootstocks and latent virus isolates are underway. Preliminary data was taken from a test grafted last summer, grafting was done for another test, wood was harvested this winter for setting up later tests, and cuttings were propagated for grafting next spring. Finally, good progress is being made in the goal of multiple technology testing of a large panel of latent virus isolates. Ultimately, this work will allow a grower to perform a set of selected tests on a proposed field scion selection, yielding an estimate of the risk of using it before it is grafted, and enabling better decision making when selecting a rootstock. Another valuable result of these studies will be to provide published information correlating new technology with the tests which are currently the regulatory standard. In turn, this will allow the new methodologies to be applied to federal quarantine regulations and grape certification programs. Without this information, the new methodologies will not be available for use in these important areas. Trials of specific latent virus effect on important rootstocks will establish the level of disease impact from specific latent viruses and providing nurserymen and growers with essential information about risk management.