Optimization of factors influencing in vitro immature seed germination in Chionanthus retusus

Chionanthus retusus is a small deciduous tree that is widely used in landscaping due to its beautiful white spring flowers and ornamental value. Conventional propagation through seeds requires one to two years of breaking dormancy. The objective of this study was to determine the conditions of in vitro germination in C. retusus. In vitro embryo culture was carried out to investigate the effects of six factors: basal media (McCown Woody Plant Medium (WPM) and Murashige and Skoog (MS)); plant growth regulators (different combinations and concentrations of naphthaleneacetic acid (NAA), 6-Benzylaminopurine (BA), and gibberellic acid ($GA_3$)); embryo age (collected weekly beginning 36 days after fruit setting); low temperature pretreatment (storing $4^{\circ}C$ for 1, 2, 3, and 4 weeks); coconut additives (100, 200, and $300ml{\cdot}L^{-1}$); and genotype (grouping plants depending on their flowering nature). The basal medium used in this study was WPM with $2mg{\cdot}L^{-1-1}\;GA_3$, $20g{\cdot}L^{-1}$ sucrose, and $6g{\cdot}L^{-1}$ Agar. WPM medium mixed with $GA_3$, resulted in higher germination rate as compared to when using a combination of auxin and cytokinin. $GA_3$ at $2mg{\cdot}L^{-1}$ was the most effective of all combinations and concentrations of PGRs. WPM medium with $2mg{\cdot}L^{-1}GA_3$ resulted in better and faster germination (75.93%). Embryos collected at 57 days after fruit setting had the highest percent of germinated seeds (87.04%) while low-temperature pretreatment of fruits at $4^{\circ}C$ for two weeks produced the highest germination (95.37%). These results of this study could be an open ground for development of an efficient protocol for commercial production of the ornamental tree.