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 5212 candidate grape rootstock seedlings (representing 34 different populations) for resistance to aggressive root-knot nematodes. We select only those seedlings which completely suppress nematode reproduction and show zero nematode egg masses. The nematode resistance evaluation total includes 494 seedlings of a genetic study population that also are qualified for consideration as rootstocks. Selected seedlings are propagated and then planted into the vineyard. We tested the propagation ability of 123 selections (already tested once for nematode resistance). We evaluated 22 selections, grafted to Syrah, in replicated rootstock trials at the University of California Kearney Agricultural Research and Extension center. We pollinated 412 clusters of crosses in 48 unique combinations specifically aimed at the breeding of improved rootstocks with resistance to aggressive root-knot nematodes and collected 33,530 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.