Somatic Embryogenesis of Selected Pinus Species: Developmental Stages of Pinus peuce and Pinus heldreichii

Somatic embryogenesis (SE) represents the most efficient and scalable technology for the mass clonal propagation and genetic improvement of superior conifer genotypes, which is crucial for meeting global wood demand and supporting forest adaptation to climate change. Despite its immense potential, SE in the genus Pinus still faces major limitations, including low initiation frequencies, restricted explant availability, and pronounced genotype dependence. This review synthesizes current knowledge on the factors influencing SE in Pinus species, with a specific focus on two ecologically vital Tertiary relicts endemic to the Balkan Peninsula: Pinus peuce (Macedonian pine) and Pinus heldreichii (Bosnian pine). For these species, traditional vegetative propagation methods are difficult or ineffective, making SE the priority approach for clonal propagation. Detailed studies on these species revealed that SE induction is highly dependent on the explant type and developmental stage. Successful embryogenic tissue formation was achieved only from whole megagametophytes containing immature zygotic embryos, within a narrow developmental window spanning 4–10 weeks post-fertilization. Furthermore, medium composition, particularly reduced ammonium concentration, proved critical for P. heldreichii success. These findings underscore the need for continued, species-specific optimization to overcome current bottlenecks and realize the full potential of SE for the conservation and sustainable clonal forestry of these high-value pines.