MOLECULAR AND BIOLOGICAL CHARACTERIZATION OF AN ISOLATE OF APPLE STEM PITTING VIRUS CAUSING PEAR VEIN YELLOWS DISEASE IN TAIWAN
Z.-B. Wu, H.-M. Ku, C.-C. Su, I.-Z. Chen, F.-J. Jan
Symptoms of vein yellows were observed on the leaves of the domestic pear cultivar, Pyrus pyrifolia var. Hengshen, in central Taiwan. A virus with filamentous particles ca 12×800 nm in size (isolate VY1) was recovered from one symptomatic leaf and established in Chenopodium quinoa. VY1 was confirmed to cause pear vein yellows by back inoculation. Sequence analysis of the cloned coat protein (CP) gene of VY1 revealed 80.5-86.7% amino acid identity with comparable genes of 19 reported Apple stem pitting virus (ASPV) isolates. A conserved region of 220 amino acids was identified at the C terminal of the CP genes of these 20 viral isolates (3'-CP region). Three German isolates, two Polish pear and apple isolates as well as 13 other ASPV isolates were divided into four groups, A, B, C and D, respectively. Isolates included in each of the groups A, B, or C shared 97.3-100% amino acid identity in the CP gene. Sequence comparisons of CP genes at the inter-group level, showed 74.8-91.2% and 79.4-93.7% nucleotide and amino acid identity, respectively. However, when the nucleotide and amino acid sequences of the 660 nt 3'-CP conserved regions were compared, sequence identity values rose to 81.1-95.5% and 91.8-99.1%, respectively. Using 3'-CP conserved regions for nucleotide and amino acid sequence identity comparison among ASPV isolates provides better demarcating criteria for the taxonomy of ASPV. This is the first report of ASPV causing pear a disease in Taiwan.