Evaluating Grape Rootstocks for Nematode Susceptibility

In California grape production is one of the perennial high-value commodities. Because of the traditional long time period a vineyard is cultivated, soil-borne pests and diseases have ample time and opportunity to build-up and be major yield constraints. Once introduced in vineyard soil, these soil-dwelling parasites can reproduce on susceptible plant roots copiously. Typically multiple species including Meloidogyne spp. (root-knot nematodes), Mescocriconema xenoplax (ring nematode), Xiphinema americanum or X. index (dagger nematode), and Tylenchulus semipenetrans (citrus nematode) and others occur in various combinations in vineyard soil and damage the crop. Once they are established in an existing vineyard they are difficult to manage because they colonize at least the upper 5-ft soil layers. Genetic resistance in rootstocks can offer protection from these culprits, and offer sustainable and efficient protection of the risk of nematode damage. The frequent co-occurrence of multiple plant-parasitic nematode species makes attaining highest levels of resistance against such nematode assemblies tedious. Typically, the resistance towards one species has limited to no effect on a different species. In the current project, selections of grape rootstock genotypes selected foremost under greenhouse conditions were exposed to field populations of nematode assemblies. In 2019, one experimental vineyard was planted following a >30 year old planting of Thompson seedless grape. A total of seventeen experimental rootstocks developed in Dr. Andrew Walkers program were planted alongside repeat entries from prior experimentation and longer-tested GRN1, GRN2, GRN4 (A. Walker) and 1017A. In addition, Zinfandel, St. George, Harmony, Flame, and Salt Creek were planted as commercial controls. In mid-June 2019, rootstocks were planted in randomized complete block design with five replications into this nematode-infested site. A month after planting, each planting site receive additional root-knot nematode-infested soil to boost the infestation levels. In 2020, another nine experimental rootstocks with similar controls were planted, and additionally inoculated with infested soil. First nematode assessments were done in the dormant season. Field testing these rootstock candidates will provide important information on the nematological and horticultural status of them. These activities will allow to identify elites that warrant further characterization, and that could add new so urgently needed rootstocks for the industry.