Recombination events in RNA2 of GFLV and ArMV in grapevines affected by yellow mosaic

Grapevine fanleaf virus (GFLV) has strains associated with distorting (Mf) and chromogenic (YM) syndromes, which are indistinguishable physico-chemically and serologically, induce the same symptoms in herbaceous hosts and have the same vector (Xiphinema index). Sequences of the RNA-2 A gene (homing protein) of Mf and YM isolates of Italian and foreign origin were compared for detecting possible regions of variability that would allow designing molecular tools (probes and/or primers) for their differential identification. Phylogenetic trees constructed with 2A sequences showed two major clusters, each comprising two subgroups. Sequence alignment of sub-group c (YM) and d (Mf) showed the presence in YM isolates of a short sequence fragment (164 nt) that differed markedly from that of the comparable region of Mf isolates. This region had 100% identity with a comparable fragment of two grapevine isolates of Arabis mosaic virus (ArMV) and no apparent homology with any of the sequenced GFLV isolates. Computer-assisted analysis of 2A sequences showed that subgroup c isolates are recombinants between GFLV and ArMV.