GRAPEVINE LEAFROLL-ASSOCIATED VIRUSES AND GRAPEVINE VIRUS-A IN SELECTED VITIS-VINIFERA CULTIVARS IN NORTHERN ITALY

The occurrence of grapevine leafroll-associated virus 1 (GLBaV-1), gra pevine leafroll-associated virus 3 (GLRaV-3) and grapevine virus A (GV A) was demonstrated in a viticultural region of northern Italy (Emilia -Romagna) using immunoelectron microscopy. Virus incidence was subsequ ently assessed using ELISA. A total of 60.6% of the 150 clone selectio ns tested, from 18 local Vitis vinifera cl cultivars, were found to be infected. ELISA did not reveal the presence of grapevine leafroll-ass ociated virus 2 (GLRaV-2) or grapevine leafroll-associated virus (GLRa V-5). GLRaV-1, GLRaV-3 and GVA were found individually and in various combinations. The most common findings were GLRaV-1 alone (25.3%) and associated with GVA (33%). Serological data confirmed that the majorit y (91%) of the clones known to be affected by grapevine leafroll (GLR) , on its own or in association with rugose wood (RW), contained viruse s, On the other hand, where the RW phenomenon was present on its own, only 40% of these clones were ELISA-positive. The implications for the biology of GLR and RW are discussed and the complex aetiology of thes e grapevine diseases is confirmed.