Abstract

The combined effect of thermotherapy and tissue culture was evaluated on Red Globe variety infected with Grapevine leafroll associated virus 2 Red Globe strain (GLRaV-2-RG). Five plants, derived from a positive mother stock plant to GLRaV-2-RG, previously verified by RT-PCR were subjected to 20, 40, 60, 80 and 100 days at 38°C and 75% RH. In each period, shoots were excised from a newly formed shoots and the apical buds of the new shoots were established in vitro. Thereafter they were subsequently transferred to a rooting medium and acclimated in a greenhouse. Ten acclimated plants were obtained for each thermotherapy period and when once the plant canes were lignified, the phloem was used to carried-out DAS-ELISA test. Plants which resulted negative for this test were submitted to a RT-PCR test. Shoot growth was observed after 20 days on thermotherapy, and the highest shoot growth was obtained after 60 days. After this maximum growth, plants began to fade towards at 80 and 100 days heat treatment. After 20 days of thermotherapy, 10% of GLRaV-2-RG-free plants were recovered and 60% after 40 days. None of the other periods produced healthy plants. This result shows that not only the exposure time to high temperatures is effective to obtain GLRaV-2-RG - free plants, but the shoot growth rate is also important. Thus, it becomes evident that the combination of thermotherapy with tissue in vitro culture is an effective tool to obtain GLRaV-2-RG-free Red Globe plants.