Somatic Embryogenesis and Plant Regeneration of Rhododendron fortunei

Rhododendron fortunei Lindl. is a popular woody ornamental plant cultivated for its pink to pale pinkish-lilac or rose colored flowers with a sweet-scented fragrance. It has also been widely used as parents for producing hardy and fragrant hybrids. Current propagation of this species has been primarily carried out through seed, stem cutting or in vitro multiplication; however, a protocol for regeneration through somatic embryogenesis has not been established. This report describes successful plant regeneration of this species through direct somatic embryogenesis. Somatic embryos formed at and around the cut surface of leaf and petiole explants of R. fortunei spp. fortunei cultured on woody plant medium (WPM) supplemented with TDZ and NAA. Somatic embryo occurrence and embryo conversion rates were 96% and 67%, respectively for leaf explant cultured on the medium supplemented with 0.5 mg/L TDZ with 0.2 mg/L NAA, and up to 35 plantlets were produced per explant. Petiole explants cultured with 0.5 mg/L TDZ plus 0.1 or 0.2 mg/L NAA had somatic embryo occurrence rates above 95% and embryo conversion rates 80% or higher, and close to 20 plantlets were produced per explant. Plantlets produced abundant hair roots ex vitro in a soilless substrate and grew vigorously in a shaded greenhouse. This established method was not only efficient in rapid propagation of a large number of plants but also potentially be useful for improving the ornamental value of this species through genetic transformation.