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Investigating Seed Dormancy in Pinus bungeana Zucc. ex Endl.: Understanding the Contributions of Enclosing Tissues and Temperature on Germination

Pinus bungeana Zucc. ex Endl. is an endangered conifer tree species that is endemic to Western Central China. With the aim to confirm whether the Pinus bungeana seeds were dormant or not, an isolated embryo was cultured and seed coat interference with imbibition was examined by the water uptake test; the contribution of enclosing structures to germination inhibition and the effect of different temperatures (10 °C, 15 °C, 20 °C, 25 °C, and 30 °C) on seed germination were investigated by the germination test, then total germination percentage (TGP) and mean germination time (MGT) were calculated. Results showed that the Pinus bungeana seeds were non-dormant, seeds without any prechilling treatment germinated readily and achieved high germination (approximately 90%) at favorable temperatures (15 and 20 °C). At 25 °C, seed germination was inhibited and intact seeds exhibited 5% germination, but an interference with imbibition was not responsible for this result. In the seed tissue removal experiment, cracking the seed coat did not improve germination effectively, removing the seed coat and leaving the nucellar membrane either intact or having a quarter of it removed both elicited greater germination (34.7% and 40%, respectively). Meanwhile, removing the seed coat and removing either half or all of the nucellar membrane both promoted higher germination (approximately 80%), with germination rates that were nearly the same as that for the isolated embryos (86%). Germination inhibition was mainly induced by the enclosing structures and the nucellar membrane played an important role in inhibiting germination.