Effect of early spring birch bud type on post-thaw regrowth after prolonged cryostorage

Early spring buds of silver birch (Betula pendula Roth), collected with and without a female catkin in the middle of April, were cryopreserved using slow cooling followed by immersion in liquid nitrogen at -196°C for 8 days, 6 months, 1 year, 3 years, or 5 years. After fast thawing the buds were cultured in vitro according to the published protocol. The regrowth ability of the two types of buds was different. The regrowth of vegetative buds without a female catkin was good after all the cryopreservation times. There was a significant decrease in the regrowth ability of buds growing in the axil of a female catkin compared with the corresponding unfrozen controls after 1 year in cryostorage. In addition to the effect of the presence of a catkin on the regrowth ability, the late collecting time of the buds also probably decreased the regrowth and regrowth rates of both types of bud. The regrowth rates of buds without a catkin were 66, 67 and 24% after 1, 3, and 5 years of cryostorage, respectively, while those of buds with a catkin were 13.5, 32, and 2.6%, respectively.

Survival and regeneration of dormant silver birch buds stored at super-low temperatures

Cryopreservation was developed for the storage of in vivo buds of silver birch (Betulapendula Roth). The principles of the optimized method were the use of buds already acclimated in nature and slow freezing with a cooling velocity of 10 °C/h down to a terminal temperature of −38 °C. After 24 h at this temperature the buds were immersed in liquid nitrogen at − 196 °C for 8 days, 6 months, or 12 months. After fast thawing, 5 min in a water bath at 37 °C, the buds were surface sterilized and cultured according to the normal laboratory routine. The buds were examined after 2 and 4 weeks of cultivation. There were no significant differences in survival and growth between the unfrozen controls and buds stored in liquid nitrogen for different times. The growth percentage of buds without a female catkin was double that of buds with a catkin. These results indicate that cryopreservation would be an ideal method for the ex situ gene conservation of birch and retention of the juvenility of adult genotypes.

Organ culture with black cottonwood: morphogenetic response of female catkin primordia

Female catkin primordia of black cottonwood (Populus trichocarpa T. & G. ex Hook.) were cultured for 70 days on a modified Murashige and Skoog's (1962) medium in vitro. Explants 2–3 mm long, and with bud scales removed, gave the best results, many of them developing floral structures characteristic of the female sex. There was a general tendency to callus formation with increasing age of the culture, occasionally followed by a reversal to vegetative growth. Catkin primordia raised on Wolter's medium without auxin or kinetin, but with 6-benzylaminopurine, and at 250 ft-c for a 16-h photoperiod, proliferated axillary shoots in loco of pistils.