In Vitro Induction and Development of Somatic Embryos from Nucellar Embryo Explants of ‘Gunung Omeh’ Mandarin (Citrus reticulata Blanco)

Gunung Omeh mandarin (Citrus reticulata Blanco var. ‘Gunung Omeh’) is a promising local citrus cultivar from Indonesia, valued for its sweet flavor, distinct aroma, and good postharvest storability. However, its production is constrained by pest and disease pressures, including fruit flies, scale insects, and citrus vein phloem degeneration (CVPD), along with limited availability of high-quality culturing material. Somatic embryogenesis offers an effective strategy for mass propagation and as a long-term platform for genetic improvement. This study aimed to develop a somatic embryogenesis protocol using nucellar Gunung Omeh mandarin explants through three experimental stages: induction, proliferation, and maturation. Nucellar embryos isolated from 60–70 days after anthesis (DAA) fruits were cultured on MS medium supplemented with various auxins (2,4-D, NAA, Picloram) at concentrations of 10, 20, and 30 μM. The highest rate of embryogenic callus formation (76%) and largest callus size (13.1 mm) were achieved using 20 μM 2,4-D. The proliferated calli were then subcultured onto media with 0–0.6 g·L−1 malt extract, and the highest globular embryo formation (80%) occurred at 0.5 g·L−1. Maturation was induced on MS medium with 20–60 g·L−1 sucrose plus 7 μM ABA, where 50 g·L−1 sucrose resulted in the highest number of cotyledon-stage embryos (3.55) and 100% maturation efficiency. This study establishes a stepwise protocol for embryogenesis in Gunung Omeh mandarin, with optimal concentrations of 20 μM 2,4-D for induction, 0.5 g·L−1 malt extract for proliferation, and 47–50 g·L−1 sucrose for maturation. The developed protocol can serve as a foundation for future breeding programs, mass propagation, and genetic transformation of this elite cultivar.