Root pruning increased bioactive compounds of hydroponically-grown Agastache rugosa in a greenhouse

Abstract

The aim of this study was to determine the proper root pruning time and ratio for enhancing bioactive compound formation in Agastache rugosa without plant growth inhibition. The control (without root pruning) and five treatments (1, 3, 5, 7, and 9 days of root pruning before harvesting (RPBH)) with 50% root pruning (Experiment 1) and four treatments of root pruning ratios with 30, 50, 70, and 90% root length at 5 days RBPH (Experiment 2) were performed in a hydroponic culture system. The results showed that shoot fresh and dry weights did not differ significantly between the 1, 3, 7, and 9 days RPBH and the control. There were no significant differences in shoot fresh and dry weights between 30 and 50% root pruning ratios and the control. The soil–plant analysis development (SPAD) chlorophyll meter was significantly decreased under ratios of 70 and 90% and 1 and 3 days RPBH, compared to other treatments. The rosmarinic acid (RA) and tilianin concentrations of A. rugosa under 9 days RPBH with 50% root pruning were significantly (105% and 141%) higher than those of the control. The acacetin concentration under 7 days RPBH with 50% root pruning was significantly (316%) higher than that of the control, while the RA and acacetin concentrations under 30% root pruning at 5 days were significantly (108% and 251%) higher than that of the control. These results indicated that 50% root pruning at 7 or 9 days before harvesting increased the concentrations of acacetin, RA, and tilianin and 30% root pruning at 5 days before harvesting increased in the levels of acacetin and RA concentration in A. rugosa without plant growth inhibition.