Grapevine fanleaf virus and Other Old World Nepoviruses

Eleven of the 15 Vitis-infecting nepoviruses are thought to have an Old World origin, either Eurasian, i.e., Grapevine fanleaf virus (GFLV); European, i.e., Arabis mosaic virus (ArMV), tomato black ring virus (TBRV), Grapevine chrome mosaic virus (GCMV), Grapevine Bulgarian latent virus (GBLV), raspberry ringspot virus (RpRSV), artichoke Italian latent virus (AILV), and cherry leaf roll virus (CLRV); north African (Tunisia), i.e., Grapevine Tunisian ringspot virus (GTRSV); and Asiatic (Turkey and Iran), i.e., Grapevine deformation virus (GDeV) and Grapevine Anatolian ringspot virus (GARSV). Only four of these viruses (GFLV, ArMV, RpRSV, and TBRV) have ectoparasitic longidorid nematodes belonging to the genera Xiphinema, Longidorus, and Paralongidorus as recognized vectors. Whereas mechanical transfer to herbaceous indicators is readily achieved with all these viruses, their transmission through pollen and seeds is rare and does not seem to occur in grapevines. Some of these viruses (GFLV, GBLV, GCMV, GTRSV, GDeV, and GARSV) are apparently restricted to Vitis, while AILV, CLRV, RpRSV, and TBRV have a host range that includes woody and herbaceous crops, as well as weed species. All these viruses cause systemic, symptomatic infections in grapevines. Depending on the strains involved, infection with these viruses induces either chlorotic mottling and deformation of leaves and canes (by the distorting strains) or bright yellow discolorations of the leaves (by the chromogenic strains). Like all known nepoviruses, the grapevine-infecting ones from the Old World have a bipartite genome and require both genomic RNAs for infection. Planting selected stocks that have undergone sanitation and certification procedures in soils free of the nematode vectors should guarantee the sanitary conditions of new plantings for the lifespan of the vineyards. This is not the case for plantings in nematode-infested soils because removal of the roots from the previous stand and prolonged fallow period do not prevent the resurgence of the infection.