S. Karimpour - Department of Horticulture, Faculty of Agriculture, Ferdowsi University of Mashhad, Mashhad, Islamic Republic of Iran.
G. Davarynejad - Department of Horticulture, Faculty of Agriculture, Ferdowsi University of Mashhad, Mashhad, Islamic Republic of Iran.
M. Zakiaghl - Department of Plant Protection, Faculty of Agriculture, Ferdowsi University of Mashhad, Mashhad, Islamic Republic of Iran.
M. R. Safarnejad - Department of Plant Viruses, Iranian Research Institute of Plant Protection, Agricultural Research Education and Extension Organization (AREEO), Tehran, Islamic Republic of Iran.

Production of virus-free stocks is crucial for efficient management of plant viruses in cultivation of pome fruits. Regarding the importance of producing the pre-basic stocks of valuable fruit trees, pear cultivar ʽNatanzʼ, an important local pear cultivar in Iran, was selected for virus eradication. In the present study, tissue culture combined with in vitro thermotherapy and thermo-chemotherapy techniques were used for elimination of Apple Stem Pitting Virus (ASPV) and Apple Mosaic Virus (ApMV). In thermotherapy approach, in vitro shoots were initially incubated for ۵۵, ۶۰, ۶۵, and ۷۰ days in alternating temperatures (۳۲/۳۸°C), then, meristems were cultivated on meristem medium. In thermo-chemotherapy approach, in vitro shoots were incubated for ۵۰ days at ۳۲/۳۸°C, and then meristems were cultivated on a medium containing ribavirin. Virus detection by RT-PCR using specific primers was carried out after rooting and adaptation of the regenerated shoots. The percentage of survived shoots and meristem establishment were depended on thermo-duration. After ۵۵ days, ۸۳.۳۳% of shoots survived, while it decreased to ۳۳.۳۳% after ۷۰ days. Both ASPV and ApMV were eliminated after ۶۰ days of thermotherapy. Ribavirin at ۱۰ and ۲۰ mg L-۱ reduced the percentage of meristem establishment to ۵۰ and ۳۷%, respectively, compared to the control (۸۸.۸۸%). Thermo-chemothery was also effective for ASPV and ApMV eradication from pear shoots.

Meristem culture, Pear, Ribavirin, RT-PCR, Virus elimination.