New strategies for in vitro rooting and plantlet acclimatization of the 'Paradox' (Juglans regia × Juglans hindsii) rootstock.

On the acclimatization of micropropagated Juglans plantlets, values fluctuating between 0 and 80% of plant loss can be found in literature, but most studies prefer to ignore the problem. This research focuses on the Juglans hybrid ‘Paradox’ (Juglans regia × Juglans hindsii), exploiting new methodologies to minimize the failure rates on the acclimatization of in vitro rooted plantlets. Data for in vitro rooting and acclimatization are presented. Rockwool cubes, peat pressed pellets and Jiffy Preformas® were tested and compared with the traditional vermiculite moistened with the DKW nutrient solution added with Phytagel, commonly used on Juglans micropropagation protocols. These new approaches allowed the transfer of in vitro rooted plants to acclimatization with a balled-root protection, instead of the traditional bare-root procedure, significantly reducing the post-transplant stress. Information concerning plantlet/mycorrhiza association during acclimatization is also presented