Responses of micropropagated peach cultivars to thermotheraphy for the elimination of prunus necrotic ringspot virus

Peach ( Prunus persica [ L. ] Batsch ) shoot - cultures infected with prunus necrotic ringspot virus (PNRSV)were selected for evaluating the responses of in vitro grown shoots of cvs Hermosa and summerset to thermotheraphy. The survival of shoot-cultures during thermotheraphy was improved by selection of the optimum concentration of 6-benzylamino purine in the medium and optimum concentration of 6-benzylamino purine in the medium and optimum age of shoots for treatment. Alternating high and low temperature thermotheraphy regimes were more effective in decreasing virus titre than costant high temperatures. Of the regimes tested, the most effective inhibition of PNRSV combined with a high survival of shoots was obtained by applying 38°C for 16 h in light alternating with 28 °C for 8 h in darkness for 18 days for Hermosa and 22 days for Summerset. Following this treatment 90 of Hermosa and 40 of Summerset shoot-cultures were virus - free as determined by enzyme-linked immunosorbent assay. RElatively large ( about 10 mm ) apices excised from these shots regenerated into virus - free plants. The advantage of the in vitro system for thermotheraphy is discussed