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2022 HU Guo-jun et al. Journal of Integrative Agriculture 2018, 17(9): 2015–2023 are frequently associated with low virus content in infected plants. Wang et al. (2008) revealed a drastic decrease in the amounts of Raspberry bushy dwarf virus RNA in shoot tips and leaves following 5 d of thermotherapy; moreover, the amounts of viral RNA were barely detectable following 8 d of thermotherapy. The plants likely did not have time to grow significantly in 8 d and the tissues sampled at different time points were essentially the same developmentally. They speculated that it may be explained by enhanced RNA silencing, the cellular mechanism devoted to targeting and degrading viral RNA in plants, at elevated temperatures. Our results supported the same conclusion. Dong et al. (2002) reported 65% virus eradication from virus-infected apple plants using thermotherapy for 27 d. In the present study, none of the virus-free apple plantlets regenerated after high temperature treatment. The result also differed from our previously reported results (Hu et al. 2015a), in which 43.7 and 52.4% of the regenerated plants from (34±0.5)°C and (36±0.5)°C treatments were virus- free. The reasons for this difference in virus elimination efficiency are not known, although factors such as the use of shoot tips from in vitro plants as well as the different apple variety, and, perhaps, virus strain and concentration may have played a role in determining the differences in results. Moreover, the detection method also may have caused this difference (Bayati et al. 2011). In this study, RT-PCR has been used for virus detection, and to ensure accuracy, two primer pairs for each apple virus were used to increase the specificity and sensitivity of detection, while Dong et al. (2002) used enzyme-linked immuno-sorbent assay (ELISA) and indicator plants as a detection method. 5. Conclusion This experimental model allowed us to evaluate the modifications of thermotherapy. 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