Micropropagation of a mature colchicine-polyploid and irradiation-mutant of Betula pendula Roth

Tetraploid plantlets were regenerated from cultured apical and axillary buds of a 23-year-old colchicine-polyploid and irradiation-mutant Betula pendula Roth tree. Bud explants were grown on modified Murashige and Skoog medium supplemented with 2.0 mg l(-1) benzylaminopurine (BAP) and 0.01 mg l(-1) 1-naphthaleneacetic acid (NAA). The medium allowed both induction of adventitious buds and development of shoots. The cut ends of new shoots produced new buds and shoots during a 4-week culture period. The micropropagated shoots were rooted on modified Murashige and Skoog medium containing 0.1 mg l(-1) NAA as the sole growth regulator. Plantlets were transferred to a peat/soil mixture (1:1) in the greenhouse, acclimated and then transplanted to a cold frame. The regenerated plantlets had a tetraploid chromosome set (4n = 56) and an altered leaf morphology typical of colchicine-polyploid birches. The leaves were hypertrophied and asymmetrical, with curly leaf margins. The mutant nature of the parent tree was also evident in the light-green color of the leaves of the plantlets.