CRYOPRESERVATION OF IN-VITRO GROWN SHOOT TIPS OF 2 INTERSPECIFIC PRUNUS ROOTSTOCKS

Shoot tips of two in vitro grown interspecific Prunus rootstocks, Fere ley-Jaspi (R) and Ferlenain-Plumina (R), were successfully cryopreserv ed using a two step freezing method. Excised shoot tips from hardened plantlets were precultured for 24 h on solid medium (modified half str ength Murashige and Skoog medium (MS)) supplemented with 5% dimethylsu lfoxide and 2% proline. They were transferred to 1.2-ml cryotubes and treated with 0.5 ml of modified PVS2 cryoprotective solution for 20-40 min. Cryotubes were then cooled at 1 degrees C/min to -40 degrees C b efore being immersed in liquid nitrogen (LN(2)), After 1 min warming a t 40 degrees C, shoot tips were rinsed with MS medium containing 1.2 M sucrose and then plated. First regrowth occurred after 5 days and was evaluated 21 days after plating. The average rate of shoot formation was 69% and 74% for Fereley and Ferlenain respectively, compared with 86% for controls of both hybrids, The roles of several factors, especi ally hardening procedures and meristem size, in the improvement of sur vival rates, were discussed.