INVITRO-PROPAGATION OF PRUNUS-TENELLA BATSCH CV FIREHILL - CONTROL OF VITRIFICATION - INCREASE OF THE MULTIPLICATION RATE AND GROWTH BY CHILLING

The effects of different factors on the induction, accentuation and reversion of vitrification during the in vitro propagation of Prunus tenella (cultivar 'Firehill') were studied. High relative atmospheric humidity (RH) of the culture chamber induced vitrification which could be eliminated by reducing RH from 85 to 45% or by omitting 6-benzyl-aminopurine from the culture medium for one passage. The horizontal positioning of the explants on the culture medium induced vitrification. The use of Lepoivre's basal medium produced less vitrification than that of Murashige and Skoog. After several passages of shoot multiplication, a decline of the multiplication rate of non-vitrified explants occurred. The multiplication rate could be restored by applying chilling treatment (5-degrees-C) to the shoots of vitroplants for 30 days. The shoots were rooted in vitro and successfully established ex vitro. A positive after-effect of the cold treatment applied to the shoots in vitro was promotion of the growth of ex vitro established plants. A few months later, all plants flowered and their flowers were identical to those of the original mother stock plant.