Distribution of apple stem grooving virus and apple chlorotic leaf spot virus in infected in vitro pear shoots

The distribution patterns of Apple stem grooving virus (ASGV) and Apple chlorotic leaf spot virus (ACLSV) in in vitro-cultured pear plants were investigated using in situ tissue-printing hybridization (TPH) and tissue blotting immunoassay (TBIA) to detect viral RNAs and coating proteins. Both ASGV and ACLSV showed high concentrations in the tip of the pear shoots and lower concentrations in the middle stem. The highest viral RNA titers were found in the phloem parenchyma of vascular bundles. Monitoring of viral RNA concentrations was conducted on infected in vitro-cultured pear plants during thermotherapy using TPH combined with X-ray film exposure in serial cross sections. No viral RNA of ACLSV or ASGV was detected in less than 2 mm and 0.5 mm long tips, respectively. The heat treatment was less effective to reduce virus titers in the bottom shoot. The obtained results would assist in the selection of tips with proper sizes from pear shoots pre- and post-thermotherapy for the production of virus-free pear plants by meristem culture. (C) 2010 Elsevier Ltd. All rights reserved.