Establishment and optimization of the embryogenic cell suspension culture system for Taxodium hybrid 'zhongshanshan'

Taxodium hybrid 'zhongshanshan' is an improved variety with significant applications in landscaping, ecological construction and beach afforestation in China, which has a high market demand. Although somatic embryogenesis system of Taxodium hybrid 'zhongshanshan' has been successfully established, it currently lacks automation and large-scale production capabilities. Therefore, we urgently need a method that can increase the output of somatic embryos (SEs) to meet the demands of large-scale production. In this study, we utilized embryogenic tissue (ET) of Taxodium hybrid 'zhongshanshan' as research material to evaluate the effects of initial ET culture time, inoculum density, suspension culture period and orbiting speed on the suspension culture. We observed that the proliferation of ET exhibited an S-shaped curve, with the exponential phase occurring approximately on the 9th day. The cell proliferation and somatic embryogenesis efficiency were influenced by the inoculum density and suspension culture period of ET, reaching their maximum when the inoculum density was 60 mg mL-1 and suspension cultured for 1 week. Additionally, an orbiting speed of 110 rpm proved to be optimal for our suspension culture, yielding the highest fresh weight (FW), dry weight (DW), higher settled cell volume (SCV), and a well-developed embryonic suspensor mass (ESM) structure. The investigation of this suspension culture system provides valuable insights and foundations for further automation and scale culture of somatic embryogenesis in Taxodium hybrid 'zhongshanshan'.