High-efficiency somatic embryogenesis techniques for different hybrids of cut lilies

Abstract

Somatic embryogenesis (SE) is a unique method of in vitro regeneration for plant reproduction, germplasm resource preservation, and molecular-assisted breeding. Although lily is an internationally valued ornamental plant, its SE technology is still incomplete. Here, the effects of different explants, picloram (PIC) concentrations, and light conditions on somatic embryo induction, development, germination and seedling formation were studied in five Lilium varieties belonging to different hybrids. The embryo histomorphology, development and origins were observed, and a broadly efficient embryogenesis system was firstly established in Lilium. With leaf explants, all varieties tested underwent indirect somatic embryogenesis (SE). With scale explants, the Lilium Asiatic ‘Strawberry and Cream’, Lilium Oriental ‘Double Surprise’, and Lilium longiflorum Thunb. ‘White Heaven’ underwent indirect SE and the Lilium longiflorum × Asiatic hybrid ‘Eyeliner’ and Lilium longiflorum × Oriental ‘Triumphator’ underwent direct SE. Somatic embryogenesis in the above varieties involved four stages: globular, heart-shaped, torpedo-shaped, and cotyledon embryos. Two original SE pathways (endogenous and exogenous) were observed, and their appearance times differed. In indirect SE, exogenous embryos appeared first, followed by endogenous embryos; whereas in direct SE, the order was reversed. The different somatic embryo origins and the proportion of internal and external origins were closely related to the occurrence of somatic embryos by direct or indirect pathways and significantly affected the induction cycle of somatic embryos. Dark culture promoted lily somatic embryo induction, while 16 h/day light culture promoted germination, and the germination rates of all five lily varieties exceeded 90%. Murashige Skoog (MS) medium + (1.5–2.5 mg L−1) PIC + 0.2 mg L−1 1-Naphthaleneacetic acid (NAA) was suitable for SE from lily leaves and scales with an induction efficiency of 88–96%. Our research developed a widely applicable regeneration procedure for different hybrids of lily via somatic embryogenesis. Morphohistological analysis confirmed the origins, developmental stages and dynamic changes of cells during in vitro morphogenesis. This study will provide a valuable reference for the propagation of Lilium.