Optimization of miracle fruit (Synsepalum dulcificum) seed germination and mutagenesis

Abstract

Interest in miracle fruit for reducing sugar content in food and beverages is increasing, but miracle fruit genetic improvement is hindered by delayed seed germination, slow seedling growth, and a lack of readily available genetic diversity. Preliminary studies were conducted to optimize the effects of seed surface sterilization, drying time, incubation temperature, and the presence or absence of the seed coat on miracle fruit germination. Optimal 10 days germination rates and seedling growth were realized by omitting surface sterilization, decreasing postharvest drying time, incubating at 30°C, and removal of the seed coat. Removal of the seed coat alone increased germination by 53% after ten days under optimal conditions. Root and shoot lengths were maximized at 8.73 mm and 2.87 mm, respectively, after 10 days incubations under optimal conditions. Experiments using γ-ray mutagenesis were conducted as a means to create genetic diversity in this species. Irradiation levels from 0 to 600 Gy resulted in a calculated LD50 at ~70 Gy with total seed mortality at 400 Gy. Finally, the frequency of seeds with three cotyledons and double seeds (3.8% and 0.43%, respectively) were observed in multiple harvests. These findings describe conditions that increase germination percentage, maximize seedling growth rate, and establish a range of radiation levels to create miracle fruit mutation populations for the genetic improvement of this valuable species.