Effect of gibberellic acid on growth and flowering of Henckelia humboldtianus Gardner (Ceylon Rock Primrose)

• H. humboldtianus has potential to be developed as a flowering potted plant.
• Application of GA3 regulates the growth and flowering of H. humboldtianus.
• Application of GA3 improves the overall appearance of H. humboldtianus plants.

Henckelia humboldtianus Gardner (Ceylon Rock Primrose), an endemic species to Sri Lanka, is a potential new flowering potted plant. This study investigated the role of gibberellins (GA3) in controlling vegetative growth and flowering of H. humboldtianus plants. H. humboldtianus plantlets, micropropagated using leaf pieces, were treated with 25 ml of GA3 (0, 50, 100, or 200 mg l−1) four weeks and six weeks after transplanting to pots containing a soil mix of sand, top soil and coir dust at a 1:1:1 ratio. GA3 treatment resulted in a progressive decrease in the time to flowering with increase concentration. Plants treated with 200 mg l−1 GA3 exhibited early flowering (10.0 ± 0.5 days), highest number of inflorescences per plant (10.9 ± 1.8) and highest number of flowers per inflorescence (24.0 ± 0.5) compared to all the other treatments. All GA3 treatments increased the peduncle length, plant height and petiole length providing a better appearance as a potted plant compared to the untreated plants. Results suggest that GA3 can be used to improve the flowering behavior and enhance the appearance of H. humboldtianus for the marketing process as a newly introduced species.