Induction of direct somatic embryogenesis and shoot organogenesis and histological study in tree peony (Paeonia sect. Moutan)

Abstract

Tree peony (Paeonia sect. Moutan) is a world famous ornamental and economically important species, but it is recalcitrant to in vitro regeneration. Here, we present a protocol for induction of direct somatic embryogenesis (SE) and direct shoot organogenesis (SO) from zygotic embryos (ZEs) of Paeonia rockii and P. ostii. The results showed that explant genotypes, ZEs stages, sucrose and plant growth regulators (PGRs) have greatly influences on in vitro morphogenesis. The highest frequency of SE (48%) and mean number of somatic embryos (5) was obtained from mature ZE of P. rockii ‘Jing Hong’ when cultured on modified Murashige and Skoog (mMS) medium supplemented with 2.22 µM BA and 0.23 M sucrose.The proliferation can be achieved by recurrent production of embryogenic callus and somatic embryos on mMS medium supplemented with 0.89 µM BA. The germinated rate of somatic embryos was 45% on WPM medium containing 2.22 µM BA and 1.44 µM GA3 after dormancy release at 4 °C under dark for 20 days. In addition, direct SO was obtained firstly in tree peony by using a variety of cytokinins. Morpho-histological analysis confirmed the initiation, development and reserve accumulation of somatic embryos and shoots. The study will be benificial to the propagation and breeding of tree peony. Tree peony (Paeonia sect. Moutan) is a world famous ornamental and economically important species which is recalcitrant to in vitro regeneration. Direct somatic embryogenesis protocol of P. rockii ‘Jing Hong’ was developed and morpho-histological analysis confirmed the initiation, development and reserve accumulation during in vitro morphogenesis. The study will provide valuable reference for propagation and breeding of tree peony.