A broad Nematode Screen to Evaluate Four Potential Nematode Resistant Rootstocks
In 1994 we completed our three-year screening effort for “Broad Nematode Resistance.” We have identified three USDA-Fresno rootstocks having completely different parentages but each possessing broader resistance to nematodes than any of the 20 conventional rootstocks we have screened to date. In this final year our work was primarily to finish screening among the ectoparasitic nematodes Xiphinema index and several X. americanum populations. In conducting these studies we used X. index containing grape fan leaf virus. Based on ELISA tests conducted by Andy Walker we learned that three years after inoculation grape fan leaf virus was not yet present in samples from USDA 6-19B. After two years’ exposure the USDA 10-23B was ELISA positive and USDA 10-17A was ELISA negative. There are at least two exciting aspects to our results. First, in comparison to “tolerance,” which is nematode buildup without vine damage, “resistance,” which is low or no nematode buildup, reduces the opportunity for biotype development. At this time we are not aware of any nematode species of statewide importance with the ability to reproduce satisfactorily on these three rootstocks. Second, the commonality of nematode biotype development has prompted our notion that the rootstock selected to follow one vineyard should not have parentage similar to the previous rootstock. For example, we would suggest that parentage such as V. rupestris in the first vineyard should not be followed by V. riparia x V. rupestris parentage in the second vineyard. These three new rootstocks provide options for growers wishing to follow such a pest management strategy. These three rootstocks are now ready for field evaluation. Almost nothing is known about their viticultural characteristics or their susceptibility to other soil pests or soil problems.