SUMMARY 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 recov- ered 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, respec- tively. 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%, re- spectively. 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. Key words: ASPV, genetic diversity, phylogenetic analysis, pear disease, Foveavirus. INTRODUCTION Pear vein yellows (PVY) disease was believed to be induced by a virus without ultimate evidence until 1971 (Hibino and Schneider, 1971). PVY frequently occurs Corresponding author: F.-J. Jan Fax: +886.4.22854145 E-mail: fjjan@nchu.edu.tw in pear-growing areas and is caused by Apple stem pit- ting virus (ASPV) (Cameron, 1989; Jelkmann, 1994; Leone et al., 1995). ASPV, which was first reported from apple (Malus sylvestris) in 1954 (Smith, 1954), has a worldwide distri- bution in pome fruit trees (Sutic et al., 1999). ASPV is transmitted mechanically to a limited herbaceous host range and has no known vector (Brunt et al., 1996; Yanase et al., 1989). Although ASPV infections to com- mercial pome fruit trees are usually latent, susceptible ap- ple (Malus spp.), pear (Pyrus spp.), quince (Cydonia ob- longa and Pyronia veitchii), hawthorn (Crataegus monogy- na) and rowan (Sorbus discolor) (Kundu and Yoshikawa, 2006; Martelli and Jelkmann, 1998; Sutic et al., 1999) may react with growth reduction and yield losses (Stouf- fer, 1989; Yanase et al., 1990). Symptoms in apple consist of green crinkle and star crack (Desvignes et al., 1999), stem pitting of Virginia crab, and epinasty and decline of Spy 277 (Stouffer, 1989). In addition to PVY, stony pit (PSP or red mottle disease) (Nemeth, 1986; Sutic et al., 1999) and necrotic spot (PNS) (Kishi et al., 1976) are in- duced by certain ASPV strains in various pear cultivars (Nemeth, 1986; Paunovic et al., 1999). Sooty ring spot and fruit deformation in quince have also been correlated to ASPV infection (Mathioudakis et al., 2009; Paunovic and Rankovic, 1998). A survey of ASPV incidence in Czech and Moravian apple orchards showed that 28% of the trees were infected (Kundu, 2003a). Samples collect- ed from symptomless apple and pear trees in Greek or- chards revealed a 96% and 43% incidence of the virus, respectively (Syrgianidis, 1988). In China, the largest pear-producing country, about 62% of the main pear cul- tivars are infected by ASPV in the pear-growing areas of northern districts (Wang et al., 1994). ASPV is the type species of the genus Foveavirus, family Flexiviridae (Martelli and Jelkmann, 1998; Adams et al., 2004). It has flexous filamentous particles about 12×800 nm in size (Koganezawa and Yanase, 1990; Martelli et al., 2007), which contain a single- stranded positive sense RNA genome of ca. 9.3 kilobas- es with five open reading frames (Adams et al., 2004; Jelkmann, 1994; Martelli et al., 2007). High genetic vari- ability among ASPV isolates/strains was observed in the nucleotide sequences of the replicase (Rodoni and Con- Journal of Plant Pathology (2010), 92 (3), 721-728 Edizioni ETS Pisa, 2010 721 MOLECULAR AND BIOLOGICAL CHARACTERIZATION OF AN ISOLATE OF APPLE STEM PITTING VIRUS CAUSING PEAR VEIN YELLOWS DISEASE IN TAIWAN Z.-B. Wu 1 , H.-M. Ku 2 , C.-C. Su 3 , I.-Z. Chen 4 and F.-J. Jan 1 1 Department of Plant Pathology, National Chung Hsing University, 40227 Taichung, Taiwan 2 Department of Agronomy, National Chung Hsing University, 40227 Taichung, Taiwan 3 Taiwan Agricultural Chemicals and Toxic Substances Research Institute, Wufong, 41358 Taichung, Taiwan 4 Department of Horticulture, National Taiwan University, 10617 Taipei, Taiwan