Incidence of Four Important Viral Pathogens in Canadian Vineyards. Donald J. MacKenzie, Centre for Plant Health, Agriculture and Agri-Food Canada, 8801 East Saanich Road, Sidney, BC Canada V8L 1H3. Raymond C. Johnson, and Carol Warner, Centre for Plant Health, Agriculture and Agri-Food Canada, 8801 East Saanich Road, Sidney, BC Canada V8L 1H3. Plant Dis. 80:955-958. Accepted for publication 6 May 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0955.

A national survey was conducted in Canada during 1994 and 1995 for four viral pathogens of quarantine significance in grapevine. A total of 11,417 samples, collected from 637 field sites, was tested for the presence of arabis mosaic virus (ArMV), grapevine fanleaf virus (GFLV), and two viruses commonly associated with grapevine leafroll disease, grapevine leafroll associated virus types I (GLRaV-I) and III (GLRaV-IN). Nationally, the incidence of nepovirus-infected samples was low, 0.53 and 0.25% for ArMV and GFLV, respectively, and higher for the two leafroll associated viruses, 1.67% for GLRaV-I and 10.8% for GLRaV-III. Nepoviruses were found only in samples of varieties of Vitis vinifera origin or hybrid crosses, whereas GLRaV-I and GLRaV-III were found in samples of all variety types. Among the varieties tested, GLRaV-III was found primarily in samples of hybrid (14.8%) or other (including the Labrusca varieties Concord, Niagara, and Elvira) (13.5%) origin, whereas GLRaV-I was found predominantly in samples of V vinifera (4.05%) origin. The widespread occurrence of these viruses in Canada has resulted in a reevaluation of their current quarantine status.