Field evaluation of rootstocks for resistance to phylloxera and nematodes
Nine rootstock trials were harvested in coastal. Central Valley and foothill locations. Rootstocks were assessed for basic yield components and simple fruit maturity measurements. In sites where VR hybrid rootstocks are being tested for field tolerance to fanleaf degeneration complex, scions were tested by ELISA for presence of fanleaf virus. In Amador County, the Zinfandel rootstock trial is still maturing and hence crop is still being tightly regulated by pruning. The highest yielding rootstocks are AXR#1 and 1202, neither of which can be recommended for planting. Most of the remaining rootstocks are yielding approximately equivalent amounts, 16.2 to 18.9 lbs/vine. As the trial develops and becomes entirely dry-farmed this response will be monitored for change. In Lake County, the highest yielding rootstocks are 5BB, 5C and 420A, at 40-44 lbs/vine on the quadrilateral trellis. Also, 5BB and 5C, along with 101-14, are amongst the most vigorous (at 4.7 to 5.3 lbs/vine) while 110R is showing the poorest growth (2.8 lbs/vine). Severe shoot stunting was observed for the rootstocks 110R, 3309 and 101-14; the cause is unknown and will be investigated in the 1992-3 season. In Lodi, rootstocks grafted to Cabernet Sauvignon yielded 32 to 35 lbs/vine, except for St. George which yielded only 26 lbs per vine, pricipally because of fewer berries per cluster. Two VR hybrid rootstock trials were harvested in 1991, in Sonoma and Santa Clara counties. The results were similar. VR hybrids showed substantially more growth and yield than the AXR#1 controls in the fanleaf sites; the differences between the VRs and the AXR#I are greater in the older trial in San Jose. ELISA readings show that 039-16 has substantially less infection than either AXR#1 or 043-43. Therefore, 039-16 remains the only viable choice for fanleaf-infested vineyard sites. New rootstock trials have been established in Napa (Oakville Experimental Vineyard), Sonoma, Lake, Mendocino, and Monterey counties. Additional trials for San Luis Obispo, Santa Barbara, Merced, San Joaquin counties are being discussed.