Unraveling biological characteristics of flower bud differentiation and reproductive organ development, advancing genetic improvement and ameliorating cone yield in Pinus koraiensis

Korean pine ( Pinus koraiensis ) is an important ecological protection and woody oil tree species native to Northeast Asia. Periodic fruiting has a significant impact on Korean pine seed yield. Flower bud differentiation (FBD) and development are the most crucial factors affecting the fruiting of Korean pine, but little detailed report so far. This study characterized the key reproductive processes of Korean pine such as flower bud differentiation, strobilus and embryo development, in Jilin, China (42°49′N, 127°09′E), through morphological and anatomical methods. The results indicated that the physiological differentiation times of the microstrobilus and ovulate strobilus were from early July to the end of July and mid-July to early mid-August of the first year, respectively. The main development period of sex organs and cells (microsporangium, bract scale, ovuliferous scale, megaspore, and microspore) was mid-April to mid-June of the second year. The flowering period was mid-June of the second year and the functional megaspore developed into a female gametophyte after pollination. Egg cell in the female gametophyte matured in mid-June of the third year, and fertilization was completed in mid-late June. Finally, the fertilized zygote developed into a mature embryo through a series of cell division and differentiation processes in mid-September of third year. Overall, our study enriched the basic knowledge of reproductive biology of Pinaceae plants, lay a foundation for further exploring the mechanism of flowering in Korean pine, and may be used in cultural management practice to increase seed yield. • The first report of a comprehensive and systematic analysis of the reproductive biology in Pinus koraiensis. • Identifies the characteristics and phenological information of reproductive organ development of Pinus koraiensis. • Identifies the key period of floral induction to advancing sex determination studies and increase yield.