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 strains A and C), and the dagger nematode (Xiphinema index). From these selections, several candidate rootstocks with strong resistance to the individual nematode species, and some with broad resistance to two or more of the nematode species, were selected.
Of the thousands of seedlings produced from these crosses, only 14 have graduated through the rooting trial and individual nematode screening trials. 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, some of the rootstock selections resistant to all four nematodes when inoculated individually were exposed to all of the species at the same time. Preliminary results are puzzling and need to be repeated. When inoculated together there appeared to be some galling. However, there were some logistical problems in conducting these preliminary experiments. We also need to test durability of resistance to root-knot and dagger nematodes when the plants are inoculated with other nematode species, including ring, citrus, pin and lesion nematodes.