Optimization of Indole-3-Acetic Acid Concentration in a Nutrient Solution for Increasing Bioactive Compound Accumulation and Production of Agastache rugosa in a Plant Factory

This study aimed to determine the optimal indole-3-acetic acid (IAA) concentration in a nutrient solution to increase the bioactive compounds while enhancing the plant growth of A. rugosa grown hydroponically. Twenty-eight-day-old plants were transplanted in a plant factory for 32 days. The plants were subjected to various IAA concentrations (10−11, 10−9, 10−7, and 10−5 M) from 8 days after transplanting, and the control treatment (without IAA). Shoot and root fresh weights were effectively improved under 10−7 and 10−9 IAA treatments. Leaf gas exchange parameters were increased under 10−7 and 10−9 IAA treatments. Four of the IAA treatments, except 10−11 IAA treatment, significantly increased the rosmarinic acid (RA) concentration, as well as the tilianin concentration was significantly increased at all IAA treatments, compared with that of the control. Especially, the tilianin concentration of the 10−11 IAA treatment was significantly (1.8 times) higher than that of the control. The IAA treatments at 10−5 and 10−7 significantly raised the acacetin concentrations (1.6- and 1.7-times, respectively) compared to those of the control. These results suggested that 10−7 concentration of IAA in a nutrient solution was effective for enhancing plant growth and increasing bioactive compounds in A. rugosa, which offers an effective strategy for increasing phytochemical production in a plant factory.