Diversity among grapevine leafroll-associated virus 2 isolates detected by heteroduplex mobility assay

Grapevine leafroll-associated virus 2 (GLRaV-2) was detected by serological and molecular analyses in several grapevine accessions of different varieties from Italian, Greek, French and Brazilian vineyards in a 2001-2002 survey. In order to study the genetic variability among GLRaV-2 isolates in the open reading frame (ORF) coding the coat protein (CP), heteroduplex mobility assays were performed on 17 isolates and six strains used as reference. Eight diverse GLRaV-2 variants were identified among the infected grapevines tested. The most common variant was found in the majority of the samples characterized; it was indistinguishable from the reference strains from the Semillon and Pinot noir 95 accessions. GLRaV-2 variants found in Italian cvs Negro amaro and Vermentino were identical to the reference strain from cv. Muscat de Samos (Greece). Three other GLRaV-2 variants from Southern and Central Italy were different from all the reference strains. A grapevine accession from Tuscany was found to contain two diverse GLRaV-2 variants. None of the variants tested sample identical to the American strain H4 or the reference strains from cvs Chasselas 8386 (Switzerland) or Alphonse Lavallee 224 (France); the latter three accessions were different from one another. The estimated nucleotide homology in CP gene among 23 GLRaV-2 isolates was in some cases <88%.