Evaluation of Grapevine Rootstock Selections

A team of academic, government, and industry partners developed a plan to evaluate rootstock selections from a USDA­ARS rootstock breeding program. In winter 2013-14, potential rootstock selections were assessed for desirable mother vine 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. In spring 2014, 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 selections (PC0349-11, PC0349-30, PC04153-4, PC0597-13, PC0784-334, and PC0790-37) which rooted adequately and were resistant to aggressive strains of root-knot nematodes (RKNs). PC0790­37 tested positive for SyV-1 and RSP viruses, so it was forwarded to Foundation Plant Services for virus elimination; testing on that selection will resume after clean plant material becomes available. Most of the remaining selections were eliminated because they were insufficiently resistant to RKN, or they rooted poorly in both labs. Four additional rootstock selections (PC0333-5, PC0366-27, PC03155-47, and PC0495-51) were added to the high priority list based on the performance of Syrah when grafted to those stocks. In 2015, cuttings from the highest-priority selections were distributed to the cooperators to confirm rootability and RKN resistance. Based on those results, cuttings from six superior selections (PC0333-5, PC0349-30, PC0349-11, PC04153-4, PC0495-51, and PC0597-13) were judged worthy of advancing to field trials to assess their performance as grafted plants in commercial vineyards.