Different eradication effects of latent viruses by combining thermotherapy with shoot tip culture or cryotherapy in four apple cultivars
Li Liu, Xuqiang Chen, Leiyu Yan, Yuankai Jin, Lulong Sun, Yazhou Yang, Yuanji Wang, Zhengyang Zhao
Virus disease is a serious problem affecting the fruit quality and production of apple, and solutions are being actively and urgently explored. The cultivation of virus-free propagules is an important method to combat virus problems facilitating the propagation of excellent apple cultivars. In this study, the apple cultivars 'Ruiyang', 'Ruixue', 'Rui Xianghong' and 'Qinyue' were used as source materials to eradicate the latent viruses (Apple chlorotic leaf spot virus, ACLSV; Apple stem grooving virus, ASGV; Apple stem pitting virus, ASPV), investigated the different virus eradication effects of combining thermotherapy with shoot tip culture (STC) or cryotherapy. Viral status of in vitro shoots of the four apple cultivars was detected using a reverse transcription-polymerase chain reaction before an alternating temperature of 38 degrees C (day) and 30 degrees C (night) were thermo-treated. Results showed that ASGV and ACLSV present from all four cultivars, 'Rui Xianghong' and 'Qinyue' were additionally infected with ASPV. The shoot survival and regrowth rates of combining thermotherapy with cryotherapy were lower than those of STC, and decreased with the time duration of thermotherapy. The virus eradication in each of the cultivars increased with the time duration of thermotherapy, and virus eradication effect of combining thermotherapy with cryotherapy was better to eradicate the latent viruses than that of STC. Combining 4 weeks of thermotherapy with cryotherapy achieved a 100% eradication of ASPV and ACLSV, and 53% to 92% of ASGV. This study provided the best treatment method for developing new virus-free apple cultivars that will support the propagation and popularization of virus-free plant and sustainability of the apple production industry.