Production of Plum Pox Virus-Free and Prunus Necrotic Ringspot Virus-Free Regenerants Using Thermotherapy and Meristem-Tip Culture in Prunus persica L.

The plum pox virus (PPV) and Prunus necrotic ringspot virus (PNRSV) diseases contribute to profound annual decreases in total yield and fruit quality in Prunus persica L. In this study, the effects of thermotherapy (24, 27, 28, and 39 degrees C) for two durations of exposure (10 d and 15 d) followed by culturing different sizes of meristem-tip (0.2, 0.5, and 1.0 mm) explants were assessed on the elimination of both viruses in three varieties ('Alberta,' 'Redtop,' and 'Dixired'). Preliminary double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) testing indicated that among the three varieties, only 'Redtop' and 'Dixired' had already been infected by both viral diseases. Therefore, only these two varieties were subjected to virus elimination. The survival rate of explants declined drastically with increasing temperature, and the highest and lowest viabilities were observed upon exposure to 24 degrees C and 39 degrees C, respectively, in both durations and varieties tested. Although the highest viability (100%) and shoot regeneration (85%) were also observed in the 1.0-mm meristem-tip explant, the results of DAS-ELISA and reverse transcription polymerase chain reaction (RT-PCR) revealed that the greatest number of virus-free plants was achieved with 0.5-mm explants cultured following 38 degrees C thermal treatment in both varieties tested. This study indicates that virus-free plants can be efficiently obtained in P. persica L. when appropriate thermal treatment is applied and the proper sizes of meristem-tip explants are subsequently cultured.