Elimination of apple necrosis mosaic virus from potted apple plants by thermotherapy combined with shoot-tip grafting

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Apple necrosis mosaic virus (ApNMV), a newly found virus in apple, is a pathogenic factor associated with apple mosaic disease. In this study, we evaluated the elimination efficiencies of ApNMV by thermotherapy combined with shoot-tip grafting. Four potted apple varieties, Xiangfu (XF), Xiangji (XJ), Longkou no. 1 (LK), and Longwei (LW) were used as the original materials. ApNMV was detected in XF, XJ, and LK by reverse transcription-polymerase chain reaction (RT-PCR) prior to treatment. These three apple varieties also harbored apple chlorotic leaf spot virus (ACLSV), apple stem grooving virus (ASGV), and apple stem pitting virus (ASPV). The four apple varieties were subjected to thermotherapy at 38 ± 1 °C. The ApNMV titer in LK during thermotherapy was quantified by quantitative real-time RT-PCR. The results showed that the titer of ApNMV markedly decreased after only 1 day of 38 °C treatment and could hardly be detected after the end of thermotherapy, but the virus was able to recover after the plants began to grow normally. The shoot tips were grafted onto rootstock after thermotherapy. The survival rate across all grafted shoot tips was 66.7% (52/78). The average elimination rate of ApNMV was 89.5% (34/38). The four viruses were ranked, from highest elimination efficiencies to lowest, ACLSV > ApNMV > ASPV > ASGV. This combination of thermotherapy and shoot-tip grafting will be helpful for the elimination of ApNMV.