VITICULTURAL CHARACTERISTICS OF VR HYBRID ROOTSTOCKS IN A VINEYARD SITE INFECTED WITH GRAPEVINE FANLEAF VIRUS

Two Vitis vinifera x Muscadinia rotundifolia hybrids (VR hybrids), 039-16 and 043-43, were tested for resistance to fanleaf degeneration over a 12-year period in the Napa Valley, California. Data comparing the vegetative growth and crop yields of these two VR hybrids to the fanleaf susceptible rootstocks AXR#1, Harmony, St. George and L171-6 (a LIDER selection) are presented for the last 8 years of the trial. Certified virus-tested Cabernet Sauvignon was used as the scion variety. Both VR hybrids became highly infected with grapevine fanleaf virus (GFLV) over the course of the trial, but neither showed the reduced crop yields associated with fanleaf degeneration. Information on the resistance of these two rootstocks to other soil-borne pests is also presented. Preliminary studies indicate that O43-43 may be susceptible to phylloxera, therefore, in sites infected with fanleaf degeneration and with potential for infestation with phylloxera, O39-16 is the only suitable choice.