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Genome Diversity and Intra- and Interspecies Recombination Events in Grapevine fanleaf virus

First, second, and fourth authors: Department of Plant Pathology, Irrigated Agriculture Research and Extension Center, Washington State University, Prosser, WA 99350; and third author: United States Department of Agriculture--Agricultural Research Service, Horticulture Crops Research Laboratory, Corvallis, OR 97330.

Grapevine fanleaf virus (GFLV) was documented in self-rooted vines of four grapevine (Vitis vinifera) cultivars in eastern Washington. GFLV was found as mixed infection in cvs. Pinot Noir, Chardonnay, and Cabernet Franc and as single infections in cv. Merlot. Fanleaf disease symptoms were only observed in the first two cultivars. The spatial distribution of GFLV-infected grapevines was random, suggesting primary spread through planting virus-infected cuttings rather than infield transmission. RNA1 sequences of Washington isolates showed 87 to 89% nucleotide sequence identity between them and with strain F13. RNA2 of Washington isolates was variable in size, showing 85 to 99% sequence identity between them and 81 to 92% with other isolates. As in other GFLV isolates, three conserved putative stem-loop structures were present in the 5′ noncoding regions of both RNAs of Washington isolates. Phylogenetic incongruence of GFLV isolates from Washington in 2A^HP- and 2B^MP-based trees and identification of putative recombination events suggested that their genomic RNA2 originated from inter- and intraspecies recombination events between GFLV, Grapevine deformation virus, and Arabis mosaic virus. These results confirm interspecies recombination in RNA2 of grapevine-infecting nepoviruses as an important strategy for GFLV evolution.