Effect of short-duration microwave treatments on flower development and secondary metabolite production in Agastache rugosa

This study investigated the effects of short-duration microwave (MW) exposure on growth, photosynthesis, antioxidant activity, and secondary metabolite accumulation in Agastache rugosa cultivated in a deep flow technique hydroponic system. Plants at 14 and 18 days after transplanting were exposed to MW radiation at 200 W for 5, 10, 15, 20, and 25 s, with untreated plants serving as the control. While most vegetative growth parameters were unaffected, MW exposure for 15–25 s significantly increased flower branch number by 9–15% and flower biomass by 9–24% compared with the control. These treatments also enhanced net photosynthetic rate (by up to 53%), chlorophyll a content (by 12%), and total phenolics (by 43–85%) compared with the control. Antioxidant enzyme activities were markedly elevated, with SOD, POD, and CAT increasing by up to 66%, 49%, and 103%, respectively. MW exposure also promoted phytochemical accumulation: total flavonoids increased by 7–11%, and key bioactive compounds such as chlorogenic acid (up to 7.3-fold), tilianin (up to 53%), and rosmarinic acid (up to 42%) were significantly enhanced. These results indicate that short MW exposures of 15–25 s act as an effective elicitation strategy to improve flower development and phytopharmaceutical quality of A. rugosa under controlled cultivation conditions.