Somatic embryogenesis and plant regeneration in Betula platyphalla

Betula platyphylla is a native tree species in northern China that has high economic and medicinal value.We developed an efficient protocol for the induction of somatic embryogenesis in B.platyphalla from immature zygotic embryos and assessed the effects of explant type,genotype,and plant growth regulators(PGRs)on embryogenic callus induction.Among the various explants evaluated,embryogenic callus was only produced from mature and immature zygotic embryos on medium with added 2,4-dichlorophenoxyacetic acid(2,4-D).Supplementation of 2,4-D-containing medium with cytokinins increased the frequency of embryogenic callus induction.On the 20 days after pollination,immature zygotic embryos that had been collected in mid-May yielded embryogenic tissue at the highest frequency(16.8%)when cultured on half-strength MS medium supplemented with 2.0 mg L^(-1)2,4-D and 0.2 mg L^(-1)6-benzylaminopurine(6-BA).The process of proliferation of embryogenic callus,somatic embryo formation,and subsequent plantlet conversion occurred under optimal culture conditions.When regenerated plants weretransplanted to soil,95%of them developed normally and grew vigorously.This somatic embryogenesis system required 3–4 months for the regeneration of B.platyphalla plantlets from immature zygotic embryos.