Effects of plant growth regulator treatments on quality-related traits and the establishment of cultivar-specific cultivation conditions in small- and medium-sized lily bulbs.

High-quality lilies with multiple flower buds are in demand for export, but small- and medium-sized bulbs often produce fewer buds, prompting the need for improved cultivation strategies. In this study, the effects of pre-planting plant growth regulator treatments on cut flower quality (flower bud number and length, plant height, and bulb circumference) in small- and medium-sized lily bulbs (14-16 cm) were investigated. Six lily cultivars ('Aubisque,' 'Difference,' 'Ducati,' 'Spring City,' 'Sweet Zanica,' and 'Woori Tower'), representing three lineages, were treated with 6-benzylaminopurine (BA) or gibberellin (GA) + BA at different concentrations and immersion times. Immersion in BA for 30 min significantly increased flower bud number overall (p = 0.0003), with 0.20 mM identified as the most effective concentration, but the response was strongly cultivar dependent: a significant increase occurred in only two of the six cultivars ('Spring City' and 'Sweet Zanica'), the remaining four were unresponsive, and GA+BA was ineffective in all cultivars. Machine learning models were constructed to predict flower bud number (R² = 0.558) and bulb circumference (R² = 0.915) from phenotypic traits. Correlation and principal component analysis identified shoot fresh weight and number of stem leaves as the grower-observable traits most closely associated with flower bud number, and response surface methodology was used to convert them into cultivar-specific growth targets. Pre-planting BA immersion therefore offers an economic and practical strategy for producing export-grade cut flowers from small- and medium-sized bulbs, but only in cytokinin-responsive cultivars, which must be identified before commercial adoption.