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Analysis of two Grapevine virus B (GVB)-infected LN33 hybrid grapevines revealed that a plant exhibiting clear symptoms of corky bark (CB) disease was infected with two molecular variants of the virus, whereas a plant exhibiting no disease symptoms was infected with only one variant. Sequence results indicated that the single variant in the CB-negative grapevine was also one of the two present in the CB-affected hybrid. Plant extracts from these two grapevines were used to successfully transmit the virus to N. benthamiana. After further cloning and sequencing, two clearly divergent variants were identified. Comparative molecular analysis of the variants, named here GVB 953-1 and GVB-H1, respectively, transmitted from CB-affected and consistently CB-negative plants, revealed short genomic regions, most of them highly divergent, that encoded amino acid sequences, containing significant amino acid substitutions altering the net charges of their respective proteins. Interestingly, a comparison of these variants to genome sequence data of GVB variants GVB Italy and GVB 94/971 available from the GenBank, revealed that these significant amino acid substitutions were the same for, and unique to, the variant pairs GVB 953-1/GVB Italy and GVB-H1/GVB 94/971. This despite the variants of each pair being otherwise clearly different at nucleotide and amino acid levels. In addition, both sets of variants differed substantially in their respective 3'-non-translated (3'NTR) regions. The relevance of these findings is discussed.

Grapevine leafroll-associated virus 2 (GLRaV-2), a member of the genus Closterovirus within Closteroviridae, is implicated in several important diseases of grapevines including "leafroll", "graft-incompatibility", and "quick decline" worldwide. Several GLRaV-2 isolates have been detected from different grapevine genotypes. However, the genomes of these isolates were not sequenced or only partially sequenced. Consequently, the relationship of these viral isolates at the molecular level has not been determined. Here, we group the various GLRaV-2 isolates into four strains based on their coat protein gene sequences. We show that isolates "PN" (originated from Vitis vinifera cv. "Pinot noir"), "Sem" (from V. vinifera cv. "Semillon") and "94/970" (from V. vinifera cv. "Muscat of Alexandria") belong to the same strain, "93/955" (from hybrid "LN-33") and "H4" (from V. rupestris "St. George") each represents a distinct strain, while Grapevine rootstock stem lesion-associated virus.