Stage-specific benzyladenine and gibberellic acid application enhances rhizome yield and essential oil accumulation in Curcuma aromatica

Curcuma aromatica Salisb. is a medicinal species in which rhizome yield and essential oil accumulation are strongly influenced by developmental stage and hormonal regulation. In this study, rhizome growth dynamics of white turmeric were characterized, and the stage-specific effects of benzyladenine (BA), naphthaleneacetic acid (NAA) and gibberellic acid (GA₃) were evaluated during the rapid growth period. Rhizome development was divided into three phases: slow growth (0-6 weeks), rapid growth (6-36 weeks) and growth cessation (36-42 weeks). During the rapid growth phase, applications of plant growth regulators significantly increased rhizome biomass and essential oil content in a stage-dependent manner. BA was most effective at 12 and 24 weeks, when active rhizome enlargement occurred, resulting in increased rhizome diameter and dry matter accumulation. In contrast, GA₃ showed greater effects at later stages. At 30 weeks, GA₃ markedly increased dry weight and essential oil content, while at 36 weeks, when rhizome growth approached cessation, its effect was mainly associated with enhanced dry matter and essential oil accumulation rather than fresh weight increase. Combined application strategies integrating early and late treatments resulted in the highest rhizome yield and essential oil content at harvest. These findings indicate that precise timing of plant growth regulator application, particularly at late developmental stages, plays an important role in optimizing rhizome yield and medicinal quality of C. aromatica.