Results of in vitro thermotherapy of apple cultivars

Apple cultivars 'Idared' and 'Sampion' were selected for application of in vitro thermotherapy at 39 +/- 0.5 degrees C. The presence of viruses in selected initial trees was detected by enzyme-linked immuno-sorbent assay (ELISA) and reverse transcription polymerase chain reaction (RT-PCR) before the beginning of thermotherapy. Cultivars 'Idared' and 'Sampion' were both infected with Apple chlorotic leaf spot virus (ACLSV) and with Apple stem pitting virus (ASPV). Cultivar 'Sampion' was moreover infected with Apple stem grooving virus (ASGV). Both apple cultivars were successfully multiplied in in vitro cultures on Murashige and Skoog (MS) medium with 1.5 mg l(-1) 6-benzylaminopurine (BAP). After the end of thermotherapy and transfer to ex vitro conditions, three clones of apple cultivar 'Idared' were free of both viruses (ACLSV, ASPV) according to repeated RT-PCR and ELISA. On the contrary, the same viruses (ACLSV, ASGV and ASPV) as in the initial field-grown trees were detected by RT-PCR in all four clones of cultivar 'Sampion'. Other sanitation and testing of apple cultivars will continue in the following years.