Effects of high vineyard temperatures on the grapevine leafroll associated virus elimination from Vitis vinifera L. cv. Napoleon tissue cultures

In vitro culture of shoot tips and axillary buds was used for virus elimination from the Spanish autochthonous table grapevine cultivar Napoleon which was infected by Grapevine leafroll associated virus-3 (GLRaV-3) and Grapevine fanleaf virus (GFLV). High percentages of GLRaV-3-free plants (91–100%) were obtained by establishing shoot tip cultures from infected mother plants of the 29-228, 74-16 and 77-266 clones. Lower percentages of virus-free plants (71–87%) were obtained by in vitro culture of the first, the second and the third axillary buds of the growing distal shoots. Percentages of virus-free plants obtained with both shoot tips and axillary buds varied according to the time of the year when the explants were collected and the bud position on the shoot. A increased efficiency of in vitro tissue culture methods was observed when cultures were established in summer and it was due in part to the high vineyard temperatures reached in the southeast of Spain during the hot season. GFLV- and GLRaV-3-free plants were only obtained by thermotherapy in combination with tissue culture methods from co-infected plants of the clone 39-29.