Development of Grape Rootstocks with Multiple Nematode Resistance

Rootstocks currently available for nematode resistance have either inappropriate horticultural characteristics (such as the inducement of excessive vigor in scions leading to poor production and quality) or they have insufficient resistance against aggressive nematode strains and species. Several species of plant-feeding nematodes are present in most vineyards, however few rootstocks have resistance to more than one species. Sources of resistance to root-knot and dagger nematodes have been detected in several Vitis species. Crosses made among these species in 1989, 1993 and 1994 were screened first for rooting characteristics and then sequentially against three nematode species: the root knot nematode {Meloidogyne incognita race 3), a strain of root-knot nematode that overcomes the resistance of Harmony rootstock {Meloidogyne arenaria), and the dagger nematode (Xiphinema index). We have selected several candidate rootstocks with strong resistance to the individual nematode species, and some with broad resistance to two or more of the nematode species. Candidate selections will progress to field trials for testing of resistance durability and horticultural characteristics in the coming year. Screening of candidate selections against other nematode species, and against combinations of nematode species, will proceed in greenhouse trials. Rootstock candidates evaluated in these studies are selected from Dr. Walker’s rootstock breeding program. This report addresses the nematode screening, not the breeding and horticultural components of that program.