Somatic embryogenesis of slash pine (Pinus elliottii Engelm.): initiation, maturation, germination and mycorrhization of regenerated plantlets

Slash pine (Pinus elliottii Engelm.), an important economic tree species with a high resin yield, is extensively cultivated in southern China. Somatic embryogenesis (SE) technology could hasten the breeding of P. elliottii through improving seedling quality and number, but mass production of somatic embryos remains constrained by various factors. We described an efficient SE system through indirect route and investigate the effects of genotype, phytohormones and culture condition on SE. Immature zygotic embryos of three open-pollinated mother trees collected during 2020–2023 were utilized for initiation of pro-embryogenic masses (PEMs). The initiation of PEMs was significantly influenced by seed sources (families) (p < 0.05). The addition of 2,4-dichlorophenoxyacetic acid (6 mg/L), 6-benzylaminopurine (1 mg/L) and kinetin (2 mg/L) effectively improved initiation rates by up to 15.67 ± 1.89%. Furthermore, glutamine addition to the maturation medium enhanced the yield of somatic embryos during culture. The optimum concentration range of activated carbon within the germination medium spanned from 3–4.5 g/L. Inoculation with ectomycorrhizal fungus Laccaria amethystea enhanced the root length of regenerated plantlets, reaching 7.92 ± 4.06 cm. The regenerated plantlets inoculated with Pisolithus orientalis and Xerocomus chrysenteron showed improved survival during the acclimatization phase, with 100% survival of mycorrhizae-treated plantlets after 3 months of acclimatization in the greenhouse. We clarified the SE conditions suitable for P. elliottii, and the SE system and mycorrhizal method we used can be applied to mass production of plantlets.