The vein-banding disease syndrome: A synergistic reaction between grapevine viroids and fanleaf virus

Viroid-free Vitis vinifera cultivars Cabernet Sauvignon and Sauvignon blanc were established in controlled field trials in California to evaluate the relationship between grapevine viroids and fanleaf virus for induction of the vein-banding disease. Vein-banding symptoms were observed only on vines which contained the three principal grapevine viroids, grapevine yellow speckle viroids (GYSVd-1, GYSVd-2), and hop stunt viroid (HSVd-g), as well as grapevine fanleaf virus (GFLV). Sauvignon blanc vines which contained the single viroid, HSVd-g, and GFLV were non-symptomatic indicating an absence of a correlation between HSVd-g and the vein-banding disease. The intensity of vein-banding symptoms was directly correlated with an enhanced titer of GYSVd-1 and GYSVd-2. Vein-banding and yellow speckle symptomatic as well as non-symptomatic vines in Italy contained two viroids, GYSVd-1 and HSVd-g. However, symptomatic vines displayed a higher titer of GYSVd-1 than non-symptomatic materials and vein-banding symptomatic vines were GFLV infected. These data experimentally demonstrate that expression of the vein-banding disease is induced by an unique synergistic reaction between a viroid, GYSVd-1 and a virus, GFLV