Induction and proliferation of axillary shoots from in vitro culture of Paeonia lactiflora Pall. mature zygotic embryos

Abstract

Zygotic embryos of three herbaceous peony (Paeonia lactiflora Pall.) cultivars (‘Fen Yu Nu’, ‘Zhong Sheng Fen’ and ‘Zhu Sha Pan’) were used to study embryo germination and optimum plant growth regulator (PGR) combinations for in vitro propagation and root initiation. Mature zygotic embryos (>90 days after flowering [DAF]) gave better germination and survival than immature zygotic embryos (50–70 DAF). A protocol for initiating shoot growth and axillary shoot proliferation was established using mature embryos. The best results were obtained when using excised zygotic embryos (EZEs) obtained by removing the testa and endosperm from the seed. The best medium for EZE germination (an embryo with cotyledons) was half-strength Murashige and Skoog (MS) medium (with double-strength CaCl2) supplemented with 0.5 mg L−1 6-benzyladenine (BA) and 0.5 mg L−1 gibberellic acid (GA3). The best medium for axillary shoot proliferation was half-strength MS medium (including double-strength CaCl2) supplemented with 1 mg L−1 BA and 1 mg L−1 GA3. PGR-free half-strength MS was the best medium for promoting root development on seedlings (a germinated EZE with tender leaves) and for robust in vitro seedling establishment. The acclimatization of herbaceous peony remains the most challenging step of the in vitro protocol.