Prevalence and distribution of <i> <scp>G</scp> rapevine leafroll‐associated virus 7 </i> in <scp>C</scp> hina detected by an improved reverse transcription polymerase chain reaction assay

Abstract

To determine prevalence and distribution of G rapevine leafroll‐associated virus 7 ( GLR a V ‐7) in C hina, a total of 213 grapevine ( V itis spp.) samples (92 popular cultivars) from 13 C hinese provinces and regions were tested for the presence of GLR a V ‐7 by reverse transcription polymerase chain reaction ( RT ‐ PCR ) assays and sequencing. GLR a V ‐7 was found in 40·4% of the samples, and shown to be widely distributed in major grapevine growing areas in C hina. GLR aV‐7 was found in more than 50 grapevine cultivars. Some popular grape cultivars showed a high incidence of GLR aV‐7 infection, such as M anicure F inger (100%), C abernet S auvignon (83·3%), M erlot (60%), F ujimineri (60%) and R ed G lobe (50%). The genetic variability of GLR aV‐7 isolates was characterized based on partial nucleotide sequences (nucleotides 945–1329 and 97–598 of the ORF ) of heat shock protein 70 homologue ( HSP 70h ) and 61‐ kD a protein ( p61 ) (nucleotides 1073–1572 of the ORF ) genes. The overall mean values of nucleotide diversity were low (ranging from 0·009 to 0·066), and phylogenetic analysis based on p61 showed that the GLR aV‐7 isolates segregated into three phylogenetic clusters. The results also showed that two previously described primer pairs failed to amplify a wide range of GLR aV‐7 isolates present in China. However, a new primer pair reported here, based on the p61 gene and its associated downstream intergenic region, detected more GLR aV‐7 Chinese isolates. This is the first report on the prevalence and distribution of GLR aV‐7 in China, and also provides an improved RT ‐ PCR assay for detecting the virus.