Morphophysiological Responses of Two Mustard (Brassica juncea L.) Cultivars to Foliar Application of Gibberellic Acid (GA₃) and Qualitative Analysis of Major Flavonol Glycosides

Background: Mustard (Brassica juncea L.) is a medicinal oilseed crop of the Brassicaceae family, globally used as a food spice and folk medicine. Although extensive research has already been con- ducted on gibberellin (GA) application to mustard, studies focusing on specific cultivars such as ‘Asia Jeok’, used as a leafy vegetable and kimchi ingredient, and ‘Red Frill’, used as a spice, remain limited. Therefore, in this study, we investigated the morphophysiological responses of these two cultivars to GA treatment and performed a qualitative analysis of flavonol glycosides among their bioactive compounds. Methods and Results: We performed a single foliar application of GA₃ at 0 (control), 50, 100, 150, or 200 ㎎·ℓ⁻¹ to four-week-old seedlings of two cultivars, ‘Asia Jeok’ (AJ) and ‘Red Frill’ (RF), and evaluated their morphological traits, biomass accumulation and allocation, plant quality indices, remote sensing-based vegetation indices, and OJIP chlorophyll fluorescence parameters four weeks later. GA₃ promoted shoot width and leaf expansion in both cultivars, with the strongest responses generally observed at 50 ㎎·ℓ⁻¹. Thereafter, cultivar responses diverged. In AJ plants, GA₃ at 200 ㎎·ℓ-1 enhanced shoot biomass and yielded higher values for compactness and Dickson quality index, indicating coordinated growth and structural quality improvements. In RF plants, morphological performance was most favorable at 50 ㎎·ℓ⁻¹, whereas treatment with 150 ㎎·ℓ⁻¹ GA₃ coincided with higher energy dissipation and lower performance index on an absorption basis than those in the control, suggesting a shift toward less favorable photochemical adjustment at intermediate-to-high concentrations. In addition, chemical profiling through UHPLC-PDA-ESI-MS/MS identified 11 major flavonol glycosides with distinct dominant cultivar-specific peaks. Conclusions: Our results support cultivar-specific GA₃ application to mustard crops and indicate that intermediate-to-high concentrations might unfavorably alter photochemistry.