INVESTIGATIONS ON NATURAL-RESISTANCE GENE S FOR 2 GRAPEVINE VIRUSES -THE FANLEAF DEGENERATION AND THE LEAFROLL DISEASE

A great number of grapevine varieties (734) belonging to the different classes of the Vitaceae family (American and Asian Vitis, Vitis vinif era, interspecific hybrids) was screened to identify sources of resist ance to fanleaf degeneration (GFLV and ArMV) and to leafroll disease ( GLRaV-1 and 3). Special attention was paid to Middle Eastern Vitis vin ifera sources due to the possibility that GFLV and V. vinifera evolved together in the Middle East. Inoculation was by green grafting. As th e inoculation conditions were difficult to control, we considered a va riety to be susceptible if the virus was found in at least one graft. That was true for all varieties for which the graft with a GFLV or GLR aV inoculum had been successful. It appeared to be more difficult to i noculate ArMV, possibly because the grapevine is not the principal hos t of this virus. In fact, it seems that this inoculation technique is not suitable for this type of investigation. On the one hand, the inoc ulation pressure is too strong. On the other hand, as the virus is in direct contact with the vessels, the technique does not allow to ident ify resistances that might occur in the first stage of a natural infec tion.