Direct proembryogenic masses initiation and plant regeneration from immature Torreya grandis embryos

Key message This paper provides an important direct proembryogenic mass initiation and plant regeneration method that might be supportive and stable for gene transformation and commercial production of Torreya grandis. Abstract Torreya grandis is an important and commer- cially valuable tree that is utilized as a source of essential oil and nuts. Propagation researches of T. grandis have been focused on micropropagation and somatic embryogenesis which derived from callus but limited data regarding direct somatic embryogenesis and plant regeneration are available in the literature. This study investigated the effects of plant growth regulators combinations on direct proembryogenic masses initiation and plant regeneration. Proembryogenic masses were initiated from cotyledons and hypocotyls of immature zygotic embryos directly. The frequency of direct proembryogenic masses initiation (52.6 %) was signifi- cantly greater than other treatments when the explants were cultured on Schenk and Hildebrandt medium which sup- plemented with 0.1 mg l -1 N6-benzylaminopurine, 0.1 mg l -1 Kinetin and 0.1 mg l -1 2,4-dichlorophenoxy- acetic acid. Combined application of Abscisic acid and Polyethylene glycol 6000 stimulated cotyledons formation and resulted in morphologically superior somatic embryos. Schenk and Hildebrandt medium supplemented with 10 mg l -1 Abscisic acid and 20 mg l -1 Polyethylene glycol 6000 was optimum (88 %) for somatic embryos maturation. Highest germinated somatic embryos percentage (35.6 %) was obtained on Schenk and Hildebrandt medium supple- mented with 2000 mg l -1 activated charcoal, with root and shoot lengths of 2.3 and 1.9 cm, respectively. As proem- bryogenic masses were initiated without the formation of callus, this study will aid to establish stable genetic trans- formationandwillalsobeusefulinimprovingunderstanding of the somatic embryogenesis of T. grandis.