Breeding Rootstocks Resistant to Aggressive Root-Knot Nematodes

The USDA Agricultural Research Service grape rootstock improvement program, based at the Grape Genetics Research Unit, is breeding 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. We screened candidate grape rootstock seedlings for resistance to aggressive root-knot nematodes. We select only those seedlings which completely suppress nematode reproduction and show zero nematode egg masses. Selected seedlings are propagated and then planted into the vineyard. We tested the propagation ability of 168 selections (already tested once for nematode resistance). We also screened a population, which also is qualified for consideration as rootstocks, for nematode resistance marker development. We evaluated 22 selections, grafted to Syrah, in replicated rootstock trials at the University of California Kearney Agricultural Research and Extension center. We pollinated 661 clusters of crosses in more than 60 unique combinations specifically aimed at the breeding of improved rootstocks with resistance to aggressive root-knot nematodes and collected rootstock cross seeds. Matador, Minotaur, and Kingfisher rootstocks, released by this USDA ARS grape rootstock breeding program in 2010, are being distributed by Foundation Plant Services and planted by California nurseries.