Breeding Rootstocks Resistant to Aggressive Root-Knot Nematodes

AVF Proj. ID: 362 / /Cat.: ,
Primary Investigator(s): Peter Cousins, Ph.Dby

The USDA grape rootstock improvement program, based at the Grape Genetics Research Unit, is breeding grape rootstocks resistant to aggressive root-knot nematodes. We define aggressive root-knot nematodes as those which feed on and damage the rootstocks Freedom and Harmony. In 2007 we screened 2669 candidate grape rootstock seedlings for resistance to aggressive rootknot nematodes. We select only those seedlings which completely suppress nematode reproduction and show zero nematode egg masses. These selected seedlings are propagated and then planted into the vineyard. In 2007 we planted 70 nematode resistant rootstock selections in the vineyard. These selections were identified in nematode resistance screening in 2006 and 2005. We tested the propagation ability of 105 nematode resistant selections and inoculated the 20 easiest rooting selections with aggressive root-knot nematodes to confirm the resistance of these selections. In 2007 we pollinated 1193 clusters of crosses in 87 unique combinations specifically aimed at the breeding of improved rootstocks with resistance to aggressive root-knot nematodes. An additional 305 clusters in 16 cross combinations were pollinated specifically for genetic study. We identified nematode resistant germplasm that may be parents for rootstock breeding. We sent nine nematode resistant elite selections to Foundation Plant Services (FPS) for virus testing; only virus tested plant material of our rootstocks will be released. Virus testing by FPS anticipates the release of some or all of these selections as rootstocks within several years.

Development, Testing and Introduction of Grape Rootstocks with Broad & Durable Nematode Resistance

AVF Proj. ID: 341 / /Cat.: ,
Primary Investigator(s): Howard Ferrisby

We continue toward our goal of developing and releasing grape rootstocks with broad and durable resistance to nematode species that are important in California vineyards. In previous years, we have screened rootstock candidates against the root-knot nematode (Meloidogyne incognita race 3), two strains of root-knot nematode that overcome the resistance of Harmony rootstock (Meloidogyne arenaria strain A and Meloidogyne incognitastrain C), and the dagger nematode (Xiphinema index). Fourteen rootstock candidates exhibit broad resistance to those nematodes. Those fourteen have been narrowed to a group of six with desirable horticultural characteristics and broad resistance across all the nematodes tested. During 2006, we continued to test the breadth of that resistance beyond the range of the primary screen species by evaluating the resistance of the 14 candidates to the ring nematode, Mesocriconema xenoplax, in the presence of other nematode species. We also evaluated ring nematode resistance in the parents of the current rootstock candidates and in some other Vitissources. Only two of the rootstock candidates exhibit any resistance to the ring nematode and that may not be durable when other nematodes are present. We continue to seek new sources of resistance. Field testing of the rootstock candidates continues in fields that were heavily infested with root-knot nematodes. Nematode population levels are declining in the root-zones of all rootstock candidates, indicating that reproduction of root-knot nematodes is not occurring. However, population levels of ring nematodes at the field site are high on most of the selections, underscoring the need for obtaining new sources of resistance to that nematode. Rootstock candidates have also been tested in soils from three vineyards with populations of root-knot and ring nematodes. We initiated a new series of tests to screen for sources of resistance to ring nematode. Those tests will continue in 2007.

A broad Nematode Screen to Evaluate Four Potential Nematode Resistant Rootstocks

AVF Proj. ID: 9401 / /Cat.: ,
Primary Investigator(s): M.V. McKenryby

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.

A broad Nematode Screen to Evaluate Four Potential Nematode Resistant Rootstocks

AVF Proj. ID: 9301 / /Cat.: ,
Primary Investigator(s): M.V. McKenryby

In 1993 we were unable to secure as many plants of 10-17A, 10-23B and 6-19B as we would have liked. We did, however, have enough for six replicates of each rootstock in the presence of two X. americanum populations and one A”, index population. May 1994 root observations reveal tip galls by X. index on the Cabernet Sauvignon and Sauvignon Blanc comparisons but not on the above three rootstocks. May 1994 soil samples revealed inadequate nematode populations to determine the levels of resistance in the rootstocks. This technical problem can be solved with time and more sampling. Sixteen Ramsey x Schwarzmann seedlings are currently being screened against a dozen different nematode species. Two of the 16 seedlings exhibit poor rooting ability. All work should be completed by the target date of January 1995. One can see from Table 1 how some of the more interesting rootstocks performed in comparison to industry standards of Ramsey, Freedom, Teleki 5C and Harmony. In the screening process a number of farm advisors provided us with vineyard soil having root knot nematode problems. These mixed populations revealed that although 8-1 OB performed well against three of our most aggressive root knot populations it did not succeed against common field populations of root knot. It also shows the results of a two-year study involving those rootstocks and ring nematodes indicating that each has performed at least as well as Harmony. Our data for other ectoparasites will be available within months. Based on the numbers in Table 1 we have three rootstocks with very broad nematode resistance. These include 10-17A, 10-23B, and 6-19B. Each of these has differing parentage which is an asset when it comes time to make rootstock decisions at the farm level. The 6-19B rootstock roots well but may have some vigor problems. To have a successful rootstock one must be able to protect against all root knot populations present in the field. That is the “lofty” goal of this work.