FIELD SCREENING OF GRAPE ROOTSTOCK SELECTIONS FOR RESISTANCE TO FANLEAF DEGENERATION

Fifty-five grape rootstock selections produced by L. A. Lider, nine Vi tis vinifera X Muscadinia rotundifolia (VR) hybrids produced by H. P. Olmo (both of the University of California, Davis), and three fanleaf degeneration-susceptible grape rootstocks were planted in 1979 in a si te in the Napa Valley, California, known to be infested with grapevine fanleaf virus (GFLV) and viruliferous Xiphinema index. All of these r ootstock selections were field-budded with V. vinifera cv. Cabernet Sa uvignon. The site was chosen because of the relatively uniform distrib ution of virus and vector. Shoot tips from the scions were first asses sed for the presence of GFLV in 1981 with enzyme-linked immunosorbent assay (ELISA). Yearly ELISA assessments continued through 1991. GFLV w as detected in scions on all rootstocks, but not for 10 yr in scions o n VR O39-16.