Somatic embryogenesis of Scots pine: cold treatment and characteristics of explants affecting induction

This is the first report on Scots pine (Pinus sylvestris L.) somatic embryo plants regenerated and growing in a greenhouse. The present work focused on improving somatic embryogenesis of the species by studying the factors affecting culture induction. Developmental stage of explants that were immature female gametophytes, including the zygotic embryos with suspensor tissues, was investigated in detail. The genetic background of the material, cold treatments (14 d, 1 or 2 months at +5°C) of cones including explants, as well as the plant growth regulator composition of the initiation medium, were also examined. When initiation of somatic embryogenesis was successful, the zygotic embryos in the explants were either proembryos or early embryos. Cold treatment of the cones had no significant effect on induction, nor were there any differences among the treatments with different duration, thus improving the practical applicability of the culture technique. The explants in cold-stored cones probably retained their initiation capacity due to the conversion of starch to sugars. This was observed as decreased number and size of starch grains in the megagametophytes compared with the controls. The seed family and the medium significantly affected induction success, the medium with auxin (9.1 or 13.6 μM 2,4-dichlorophenoxyacetic acid) and cytokinin (2.2 μM 6-benzylaminopurine) being better than the medium with cytokinin (5 μM 6-benzylaminopurine) alone. The significance of the genetic background of the explants and the initiation medium indicate that it might be possible to improve the initiation rates by using explants from controlled crossings between competent genotypes, and by developing more specific media for important seed families.