Cold storage of in vitro cultures of hybrid poplar shoots (Populus alba L. x P. grandidentata Michx.)

Shoot cultures of P. alba x P. grandidentata Crandon were maintained for more than 5 years at 4°C with minimal growth. The highest survival after 2 years and 5 years of cold storage were 70% and 25% respectively using 1-month of pre-storage culture on MS medium containing 1.33 M BA. When 5-year-old cold-stored shoot cultures were transferred to the greenhouse, color variations were observed. The frequencies of albino and red pigmented plants were 0.25% and 12.8%, respectively. A rosette type growth pattern was also observed on 0.3% of the long-term cold-stored plants. During long-term cold storage there were local disruption of cambium connections and the accumulations of chemicals in some cells, as observed by light microscopy.