Breeding Rootstocks Resistant to Aggressive Root-knot Nematodes
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 2006 we screened 3622 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. These selected seedlings are propagated and then planted into the vineyard. In 2006 we planted 372 nematode resistant rootstock selections in the vineyard. These selections were identified in nematode resistance screening in 2005 and 2004. In 2006 we pollinated 132 clusters of crosses specifically aimed at the breeding of improved rootstocks with resistance to aggressive root-knot nematodes. We tested the propagation ability of 114 nematode resistant selections. We confirmed the resistance of our rootstock selections to aggressive root-knot nematodes and we identified nematode resistant germplasm that may be parents for rootstock breeding.