Efficiency of virus elimination from potted apple plants by thermotherapy coupled with shoot-tip grafting

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Four varieties of potted apple were subjected to thermotherapy (37 ± 1 °C) coupled with shoot tip grafting. Using reverse transcription-polymerase chain reaction assays prior to treatment, mixed infections with Apple chlorotic leaf spot virus (ACLSV), Apple stem pitting virus (ASPV), Apple stem grooving virus (ASGV), Apple mosaic virus (ApMV) and Apple scar skin viroid (ASSVd) were detected in 95.8 % of treated plants. It was found that the sprouts of Dahongrong (DHR) and Qiyuetianxian (QYT) variety buds were inhibited by high temperature, although some buds of these two varieties were able to sprout, the growth was slow. The average survival rate of shoot tips cut after thermotherapy was 41.2 % (61/148). The survival rate of DHR (63.2 %) was highest among the four varieties. Sixty-one surviving apple plants were detected over two periods, indicative of an average elimination rate of 65.6 % (40/61) for new leaves (June) and 37.7 % (23/61) for dormant branches (November). The difference of elimination rate for DHR between the two periods was the most obvious. Detections rates of viruses were also different in the two periods; ASGV in dormant branches were 27.8 % higher than those in new leaves, and ASPV (90.6 %) remained the same over the two periods.