2019 ASHS Annual Conference

A rootstock trial was planted in the Alexander Valley in Sonoma County, CA in 2012, one year after the previous vineyard was removed due to yield loss caused by grapevine fanleaf virus (GFLV). Dagger nematode, Xiphinema index, and ring nematode, Mesocriconema xenoplax, were present in the previous vineyard. The trial site remained fallow for one year and the trellis system was left in place; no pre- or post-plant nematicide applications were made. Vine spacing is 2.1 x 3.0 m (vine by row). Eleven rootstock treatments were planted as green benchgrafts in a randomized complete block design with eight replications of five vine plots. The rootstocks evaluated were GRN1, GRN2, GRN3, GRN4, GRN5 and O39-16, which are resistant to X. index and RS-3, RS-9, Schwarzmann, 1616C and 1103P, which have medium or low resistance. Vines were trained to bi-lateral cordons and spur pruned. Pruning weights increased for nearly all rootstocks over four years (2015 to 2018) with a significant treatment by year interaction. In 2018, vines on O39-16 and GRN2 tended to have the greatest pruning weights with 4.15 and 3.46 kg/vine respectively and vines on GRN1 had the least growth of the GRN rootstocks (1.88 kg/vine). Pruning weights of RS-9, RS-3 and 1616C were 9%, 13% and 23% of those of O39-16 respectively. In 2018, vines on GRN2, GRN3 and O36-16 had the greatest yields ranging from 12.2 to 13.9 kg/vine and RS-9 and RS-3 had the lowest with 3.6 and 4.5 kg/vine respectively. Nematodes were sampled by plot in December 2018: X. index was counted in eight and M. xenoplax counted in 25 of the 48 plots for the five GRN rootstocks and O39-16. Xiphinema index was counted in 25 and M. xenoplax counted in 24 of the 40 plots of RS-3, RS-9, Schwarzmann, 1616C and 1103P. In 2017, shoot tips were sampled from each vine, and composite samples analyzed by plot for GFLV by ELISA. At least 75% of all plots of Schwarzman, 1103P and 1616C tested GFLV-positive and 38% of all plots of RS-3 and RS-9 tested positive. Combined, 45% of the GRN plots tested GFLV-positive; GRN1 had one infected plot and the remaining GRN rootstocks each had three or more. In 2018, 60% of the GRN plots tested GFLV-positive. No O39-16 plots tested positive in either year. GRN rootstocks have maintained growth and yields under GFLV pressure.