SHOOT FORMATION AND PLANT-REGENERATION OF VEGETATIVE PEAR BUDS CRYOPRESERVED AT -150-DEGREES-C

Vegetative winter buds of pear (Pyrus communis L. cv. Beurre d'Amanlis ) were successfully cryopreserved at - 150 degrees C after pre-freezin g to - 30 degrees C. Meristems were excised from the buds and cultured on medium (WPM) containing 1.0 mg.liter(-1) 6-benzylamino-purine (BA) , 25 g.liter(-1) sucrose and 0.8% (w/v) agar. Partial dehydration at 2 5 degrees C prior to pre-freezing at - 30 degrees C improved the subse quent shoot formation rate. The optimal water content of the dehydrate d buds was about 41%. Pre-freezing with a daily decrease at 5 degrees C increments to -30 degrees C followed by slowly thawing in air at 0 d egrees C was effective for producing the highest rate of shoot formati on. Micrografting of the cryopreserved vegetative buds on young seedli ngs also induced normal shoot growth. This procedure was successfully applied to twelve other cultivars of pear. Thus, this protocol of usin g vegetative buds is a simple, reliable method for cryopreserving pear germplasm.