Variability of the coat protein gene of Grapevine leafroll-associated virus 3 in Brazil

Leafroll is an economically important disease affecting grapevines (Vitis spp.). Nine serologically distinct viruses, Grapevine leafroll-associated virus-1 through 9, are associated with this disease. The present study describes the coat protein gene sequence of four GLRaV-3 isolates occurring in the São Francisco River basin, Northeastern Brazil. The viral RNA was extracted from GLRaV-3 ELISA-positive plants and the complete coat protein gene was amplified by RT-PCR. Sequences were generated automatically and compared to the complete coat protein sequence from North American (NY1) and Chinese (Dawanhong No2 and SL10) GLRaV-3 isolates. The four studied isolates, named Pet-1 through 4, showed deduced amino acid identities of 98-100% (Pet-1 through 3) and 95% (Pet-4) with North American and Chinese isolates. A total of seventeen amino acid substitutions was detected among the four characterized isolates in comparison to the NY1, Dawanhong No.2 and SL10 sequences. The results indicated the existence of natural variation among GLRaV-3 isolates from grapevines, also demonstrating a lack of correlation between sequence data and geographic origin. This variability should be considered when selecting regions of the viral genome targeted for reliable and consistent virus molecular detection. Additional keywords: Closteroviridae, Ampelovirus, GLRaV-3. RESUMO Variabilidade do gene da proteína capsidial do Grapevine leafroll-associated virus 3 no Brasil O enrolamento da folha é uma doença economicamente importante que afeta videiras (Vitis spp.). Nove vírus sorologicamente distintos, Grapevine leafroll-associated virus-1 a -9, estão associados à doença. Este estudo descreve a seqüência do gene da proteína capsidial de quatro isolados do GLRaV-3 encontrados no Vale do Rio São Francisco, Nordeste do Brasil. O RNA viral foi extraído de plantas positivas em ELISA para o GLRaV-3 e o gene da proteína capsidial completo foi amplificado por RT-PCR. As seqüências foram geradas automaticamente e comparadas a seqüências completas do gene da proteína capsidial de isolados Norte-Americano (NY1) e Chineses (Dawanhong N°2 e SL10) de GLRaV-3. Os quatro isolados estudados, denominados Pet-1 a 4, exibiram identidades de aminoácidos deduzidos de 98-100% (Pet-1 a 3) e 95% (Pet-4) com os isolados Norte-Americano e Chineses. Um total de dezessete substituições de aminoácidos foi detectado entre os quatro isolados caracterizados em comparação com as seqüências do NY1, Dawanhong No.2 e SL10. Os resultados indicaram a existência de variação natural entre os isolados de GLRaV-3 de videiras, demonstrando também a falta de correlação entre dados de sequência e origem geográfica. Esta variabilidade deve ser considerada quando se selecionam regiões do genoma viral para uma detecção molecular confiável e consistente. Palavras-chave adicionais: Closteroviridae, Ampelovirus, GLRaV-3. COMUNICAÇÕES / COMMUNICATIONS Leafroll occurs in all major grapevine growing regions of the world, reducing productivity and quality of both wine and table grapes. It is estimated that leafroll accounts for 62% of the world losses of grape production due to viruses (Little et al., 2001; Gugerli, 2003). In Brazil, grapevine leafroll is an economically important disease in the São Francisco River basin, one of the main tropical suppliers of table grapes for exportation, with 8,000 ha dedicated to grape production. Numerous reports have shown that flexuous, filamentous closterovirus-like particles ranging from 1,400 to 2,200 nm in length and ca. 12 nm in diameter are closely associated with grapevine leafroll disease. Currently, there are nine serologically distinct viruses, collectively referred to as grapevine leafroll-associated viruses and designated GLRaV-1 through GLRaV-9. GLRaV-1 and -3 are the most widespread and economically important of these viruses (Martelli et al., 2002; Gugerli, 2003).