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 2005 we screened 6201 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. We have 367 nematode resistant selections that will be ready for vineyard planting in spring 2006. In 2005 we planted 38 nematode resistant rootstock selections in the vineyard. These selections were identified in nematode resistance screening in 2004 and 2003. In 2005 we pollinated 857 clusters of crosses specifically aimed at the breeding of improved rootstocks with resistance to aggressive root-knot nematodes.