Development of Grape Rootstocks with Broad and Durable Nematode Resistance
Several species of plant-feeding nematodes are present in most vineyards, however few rootstocks have resistance to more than one species. Our goal is to develop grape rootstocks with broad and durable resistance to important nematode species. We have screened rootstock candidates against the root knot nematode (Meloidogyne incognita race 3), two strains of root-knot nematode that overcome the resistance of Harmony rootstock (Meloidogyne arenaria strain A and Meloidogyne incognita strain C), and the dagger nematode (Xiphinema index). Of 6,000 seedlings produced from crosses, only 12 graduated through the rooting trial and individual nematode screening trials with broad resistance to all four nematodes tested separately. Some of the 12 rootstocks exhibit slight root symptoms when exposed to all of the nematode species concurrently. Two remain free of any nematode symptoms. These are extremely valuable plants. We know of no other examples of rootstocks for perennial crops selected for broad (multi-species) nematode resistance. To test the durability of the resistance, the rootstock selections resistant to all four nematodes when inoculated individually were exposed to the ring nematode, Mesocriconema xenoplax. Several appeared to have some resistance to this nematode as well. Preliminary experiments suggest that the resistance to root-knot and dagger nematodes may break down at high soil temperatures in some of the selections. Further research will be necessary to define the thermal ranges for each rootstock candidate.