Effects of Gibberellic Acid and Ethephon on Flower Bud Differentiation, Endogenous Hormones, and Reserve Metabolism in LA Hybrid Lily

Abstract

Abstract Flower bud differentiation is a key developmental transition that determines flowering time and ornamental quality in lilies. In this study, we evaluated the effects of bulb-soaking treatments with gibberellic acid (GA3; 50, 100, and 200 mg L–1) and ethephon (ETH; 25, 50, and 100 mg L–1) on floral morphogenesis, endogenous hormone profiles, and carbon–nitrogen metabolism in the LA hybrid lily ‘Indian Summerset’. Among the concentrations tested, 100 mg L–1 GA3 and 50 mg L–1 ETH showed the strongest promotive effects on flower bud differentiation, advancing the completion of differentiation by approximately 10 days and advancing initial flowering by 9.0 and 5.8 days, respectively, compared with the water-treated control. These treatments were associated with stage-dependent changes in endogenous hormones, including relatively low GA3 levels during the early differentiation phase and increased ABA, IAA, and 6-BA levels during organogenesis. Accelerated differentiation was also accompanied by enhanced mobilization of bulb starch reserves and increased accumulation of soluble sugars and soluble proteins, suggesting that carbohydrate remobilization and nitrogen-containing compounds may provide metabolic support for floral organ formation. Morphologically, GA3 promoted stem elongation and increased flower number, whereas ETH induced compact growth and increased flower diameter. These results indicate that GA3 and ETH differentially regulate flowering-related traits in LA hybrid lily and that their effects are closely associated with coordinated changes in hormone balance and reserve metabolism. The findings provide physiological evidence for improving flowering regulation in lily production, although further studies using finer concentration gradients and direct ethylene/cytokinin profiling are needed to determine the precise effective treatment ranges and underlying mechanisms.