In Vitro Thermotherapy and Thermo-Chemotherapy Approaches to Eliminate Some Viruses in Pyrus communis L. cv. ‘Natanz’

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 55, 60, 65, and 70 days in alternating temperatures (32/38°C), then, meristems were cultivated on meristem medium. In thermo-chemotherapy approach, in vitro shoots were incubated for 50 days at 32/38°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 55 days, 83.33% of shoots survived, while it decreased to 33.33% after 70 days. Both ASPV and ApMV were eliminated after 60 days of thermotherapy. Ribavirin at 10 and 20 mg L-1 reduced the percentage of meristem establishment to 50 and 37%, respectively, compared to the control (88.88%). Thermo-chemothery was also effective for ASPV and ApMV eradication from pear shoots.