Optimization of In Vitro Rapid Propagation for Rhododendron decorum Winter-Flowering Mutant Stem Segments and Leaf Explant Regeneration Induction

Abstract

Rhododendron decorum Franch. has high ornamental value and emerging edible potential, but conventional propagation cannot meet the demand for high-quality, genetically uniform planting stock. This study optimized explant disinfection, adventitious bud induction, shoot proliferation, and rooting culture using stem segments and leaves from a winter-flowering naturally mutated individual of Rhododendron decorum, aiming to minimize contamination and browning. Results demonstrated that combined disinfection with 1% KMnO4 (10 min) and 10% H2O2 (4 min) outperformed single-treatment with 0.1% HgCl2. For primary culture, the optimal medium for adventitious bud induction was WPM + 30 g·L−1 sucrose + 7.5 g·L−1 agar + 0.56 g·L−1 Ca(NO3)2 + 100 mg·L−1 VC + 3 mg·L−1 TDZ + 0.1 mg·L−1 NAA, achieving an induction rate of 66.67%. During subculture, when the concentrations of TDZ and NAA were adjusted to 0.6 mg·L−1 and 0.05 mg·L−1, respectively, and 2 mg·L−1 GA3 was supplemented, stem nodes exhibited slight thickening but no significant shoot elongation. For rooting, the basal medium WPM + 20 g·L−1 sucrose + 7.5 g·L−1 agar + 0.56 g·L−1 Ca(NO3)2 + 100 mg·L−1 VC + 1 g·L−1 activated charcoal supplemented with 0.8 mg·L−1 NAA yielded superior rooting performance. Adding 2 mg·L−1 2iP tended to enhance rooting rate relative to the NAA-only treatment from an independent rooting experiment. For callus-mediated bud induction from leaves, 0.1 mg·L−1 TDZ + 0.01 mg·L−1 NAA was optimal. Notched fully expanded apical leaves from tissue-cultured plantlets showed highest adventitious bud induction under 0.3 mg·L−1 TDZ + 0.01 mg·L−1 NAA. The established micropropagation system supports bud sport variety selection, mass seedling production, and genetic transformation research.