Breeding Rootstocks Resistant to Aggressive Root-knot Nematodes
The USDA Agricultural Research Service grape rootstock improvement program, based at the rape 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. In 2010 we released Matador, Minotaur, and Kingfisher, three root-knot nematode resistant grape rootstocks. We screened 5383 candidate grape rootstock seedlings (representing 45 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. Selected seedlings are propagated and then planted into the vineyard. We planted 352 root-knot nematode resistant rootstock selections into the vineyard at the University of California Kearney Research and Extension Center. We screened an additional 25 seedlings exclusively for nematode resistance genetics studies. We tested the propagation ability of 120 selections (already tested once for nematode resistance) and of these retested 33 selections to confirm nematode resistance in replicated trials. We planted 11 selections, grafted to Syrah, into a new rootstock trial at the University of California Kearney Research and Extension Center and provided 11 rootstock selections to Foundation Plant Services for virus disease testing. We pollinated 393 clusters of crosses in 60 unique combinations specifically aimed at the breeding of improved rootstocks with resistance to aggressive root-knot nematodes.