A Broad Nematode Screen to Evaluate Four Potential Nematode Resistant Rootstocks

The USDA-Fresno was able to provide good quantities of each of the 3 rootstocks by April 1992. We also rooted lesser quantities of various USDA numbered hybrids that appeared interesting and screened those alongside. The complete root knot screening is complete as of this writing, and is presented in Table 1 attached. The Ramsey x Schwarzmann cross provided 800 seedlings. They received their first screening in January, 1993 against a moderately aggressive root knot from the Malaga area. We had 116 of these with no galls and zero root knot build-up. In April 1993 the 116 were divided into 36 of low vigor, 35 of moderate vigor, and 44 of high vigor and each screened against our three most aggressive root knot populations. 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 8-10B performed well against 3 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 2 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 in 10 months. Based on the numbers in Table 1 we already have five rootstocks with broader root knot nematode resistance than the best industry standards. These include 10-17A, 10-23B, 6-19B, 3-3A, and possibly 8-17A. 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. The 3-3A rootstocks is providing good vigor and a healthy-appearing root system. We will need to examine the mode of resistance on this one. This work is well underway and we hope the bulk of it will be completed with only 2 years of funding. In growers’ fields this year we have found at least two new root knot pathotypes which perform similar to but not exactly like the H. arenaria pathotype Harmony. 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.