Evaluation of Grapevine Rootstock Selections

A team of academic, government, and industry partners developed a plan for evaluating nearly 700 rootstock selections from a USDA-ARS rootstock breeding program. All the vines were assessed for desirable traits, including the production of abundant, well-matured canes of adequate diameter, length, and internode spacing, with minimal lateral shoot growth, powdery mildew scars, freeze damage, or fruit production. Based on these criteria, 240 vines having very poor traits were identified and discarded, and 30 selections with very good traits were prioritized for further evaluation. Cuttings from the high-priority selections were distributed to several academic and industry labs, where their rooting ability, nematode resistance, and virus status were tested. These tests narrowed the high priority list to six virus-free stocks which were resistant to aggressive strains of root-knot nematodes (RKNs). Some of the six high-priority vines rooted poorly in one or both cooperator’s labs. Weak rooting is unacceptable, and may confound nematode resistance testing, so we propose to retest these selections, using more cuttings, and benefitting from the expertise of a commercial grapevine nursery. Most of the remaining selections were eliminated because they were found to be susceptible to RKN by one or both labs, or they rooted poorly in both labs. One RKN-resistant selection rooted very well but tested positive for SyV-1 and RSP viruses, so it will be forwarded to Foundation Plant Services for virus elimination; testing on this selection will resume after clean plant material becomes available. Four additional rootstock selections were added to the high priority list based on the performance of Syrah when grafted to those stocks. Cuttings from those four selections will be distributed to the cooperators for advanced testing.