Prevalence and distribution of Grapevine leafroll-associated virus 7 in China detected by an improved reverse transcription polymerase chain reaction assay

To determine prevalence and distribution of Grapevine leafroll-associated virus 7 (GLRaV-7) in China, a total of 213 grapevine (Vitis spp.) samples (92 popular cultivars) from 13 Chinese provinces and regions were tested for the presence of GLRaV-7 by reverse transcription polymerase chain reaction (RT-PCR) assays and sequencing. GLRaV-7 was found in 404% of the samples, and shown to be widely distributed in major grapevine growing areas in China. GLRaV-7 was found in more than 50 grapevine cultivars. Some popular grape cultivars showed a high incidence of GLRaV-7 infection, such as Manicure Finger (100%), Cabernet Sauvignon (833%), Merlot (60%), Fujimineri (60%) and Red Globe (50%). The genetic variability of GLRaV-7 isolates was characterized based on partial nucleotide sequences (nucleotides 945-1329 and 97-598 of the ORF) of heat shock protein 70 homologue (HSP70h) and 61-kDa protein (p61) (nucleotides 1073-1572 of the ORF) genes. The overall mean values of nucleotide diversity were low (ranging from 0009 to 0066), and phylogenetic analysis based on p61 showed that the GLRaV-7 isolates segregated into three phylogenetic clusters. The results also showed that two previously described primer pairs failed to amplify a wide range of GLRaV-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 GLRaV-7 Chinese isolates. This is the first report on the prevalence and distribution of GLRaV-7 in China, and also provides an improved RT-PCR assay for detecting the virus.