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.
In vitro conservation and propagation of Betula pendula Roth var. carelica (Mercklin) Hamet-Ahti
