Plant regeneration by somatic embryogenesis in Pinus thunbergii resistant to the pine wood nematode

Abstract

Pine wilt disease (PWD) is a severe threat to pine forests in East Asia. Screening and breeding of resistant varieties is a very effective way to prevent and control PWD; however, no reliable somatic embryogenesis system has yet been developed for the elite nematode-resistant Pinus thunbergii Parl. line. In this study, we studied the plant regeneration via somatic embryogenesis of nematode-resistant P. thunbergii. Initiation of embryogenic tissue was significantly affected by seed family (p = 0.017), immature zygotic embryo stage (p = 0.032), and initiation medium (p = 0.004). Seed family 37 was the most favorable female parent for initiation of P. thunbergii. Furthermore, the initiation rate increased from the pre-embryonic stage to the cleavage polyembryonic stage. The optimal medium was I2, containing 2,4-dichlorophenoxyacetic acid (9 μmol·L−1) and 6-benzyladenine (4.4 μmol·L−1). A statistically significant interaction between cell line and subculture time (24 months) was observed in the influence on proliferation rate, somatic embryo production, and percentage germination (p < 0.001). In this study, the highest somatic embryo production was achieved using cell line 37-1 (1983 somatic embryos per gram fresh mass), with approximately 83.5% of somatic embryos germinating after transferring to germination medium, of which 77.6% converted into plantlets.