Micropropagation of Fragrant Rhododendron fortunei Via in Vitro Shoot Culture

Rhododendron fortunei Lindl. is native to China. Since its collection by Robert Fortune in the 19^th century, this species has been increasingly produced for its showy and sweet-scent fragrant flowers and tolerance to low temperatures. It is propagated through seeds or stem cuttings. Seed propagation may produce plants that are not true-to-type, and cutting propagation has low survival rates. This study was carried out to develop a method for in vitro micropropagation of this species. Young stem cuttings of R. fortunei ssp. fortunei with two nodes were cultured on Anderson, Murishige and Skoog, McCown’s Woody Plant (WPM), and Economou and Read media supplemented with 4 mg/L zeatin with or without 1.0 mg/L NAA. Numbers of axillary shoots produced on WPM and Econmou and Read media were similar but significantly higher than the other media. Economou and Read were subsequently used for improving shoot multiplication rates with zeatin at 0, 2, 4, and 8 mg/L in combination with 0 or 1.0 mg/L NAA. Up to 10 axillary shoots were produced per explant cultured on the medium containing 4.0 mg/L and 1.0 mg/L IAA. The shoots were rooted in half-strength Economou and Read medium supplemented with 0, 1, and 2 mg/L IBA. The rooting percentage was 100% in 60 days after shoots were cultured on the medium containing either 1.0 IBA or 2.0 mg/L IBA, and average root numbers were up to 10.83. Plantlets were transplanted into a soilless substrate and grown in a shaded greenhouse. Micropropagated plants were morphologically stable and grew vigorously with a 95% survival rate. This established method could be used for rapidly propagating disease-free liners and for speeding up new plant introduction and new cultivar release of R. fortunei.