The objective of this study was to determine the proper electrical conductivity (EC) of a nutrient solution (NS) for accumulating bioactive compounds of Agastache rugosa without decreasing plant growth. Six-week-old seedlings were transplanted in a deep flow technique system with Hoagland NS with a 2.0 dS·m⁻¹ EC for the initial week. From eight days after transplanting, the plants were treated with six EC treatments of 0.5, 1.0, 2.0, 4.0, 6.0, and 8.0 dS·m⁻¹ for three weeks. Plant growth parameters, leaf gas exchange parameters, the relative chlorophyll value, and the ratio of variable to maximum fluorescence (F_v/F_m) were measured, and the rosmarinic acid (RA), tilianin, and acacetin concentrations were analyzed at 28 days after transplanting. The results showed that almost all plant growth parameters were maximized at 2.0 and 4.0 dS·m⁻¹ and minimized at 8.0 dS·m⁻¹ compared with the other EC treatments. The relative chlorophyll and F_v/F_m values were maximized at 2.0 and 4.0 dS·m⁻¹. Similarly, leaf gas exchange parameters were increased at 2.0 and 4.0 dS·m⁻¹. The RA content exhibited significantly higher values at 0.5, 1.0, 2.0, and 4.0 dS·m⁻¹ compared with other treatments. The tilianin and acacetin contents exhibited the significantly highest values at 4.0 and 0.5 dS·m⁻¹, respectively. These results suggest optimal EC treatment at 4.0 dS·m⁻¹ for increasing bioactive compounds in A. rugosa plants without decreasing plant growth. Excessively high or low EC induced salinity stress or nutrient deficiency, respectively. Furthermore, among the plant organs, the roots of A. rugosa contained the highest RA concentration and the flowers contained the highest tilianin and acacetin concentrations, which revealed a higher utilization potential of the roots and flowers for bioactive compounds.

Plants respond to root temperature stresses by producing antioxidants as a defense mechanism. Since a number of these are phytochemicals with enhancing effects on human health, we examined the effects of 4 root-zone temperature (RZT) treatments (10, 20, 28, and 36 °C) on plant growth and the main bioactive compound concentrations in each organ of Agastache rugosa plants. We aimed to determine the optimal RZT treatment to increase bioactive compound concentrations with no deleterious effects on plant growth. Four-week-old seedlings were grown in a plant factory for 32 days. Nine plant growth parameters, namely, shoot and root fresh weights, stem and root lengths, leaf length and leaf width, leaf area, and shoot and root dry weights were significantly decreased at 10 and 36 °C compared with other treatments. A similar pattern was observed for the chlorophyll content and leaf gas exchange parameters. Of all the RZT treatments, RZT at 28 °C produced the significantly greatest accumulation of two major bioactive compounds, namely, rosmarinic acid (RA) and tilianin contents per the A. rugosa plant, and had no adverse effects on the overall growth of A. rugosa. This supports the use of 28 °C RZT to successfully improve the bioactive compounds with no adverse influence on plant growth or yield.

Hemp (Cannabis sativa) has gained global attention since being legalized in the USA in 2018. The legalization of hemp is also underway in Korea; however, it requires facility cultivation and an agricultural technological system that can produce high-quality plants. This study investigated the changes in the growth and secondary metabolite content of female hemp following treatment with the plant growth retardant diniconazole (DIN). Treatment with DIN decreased the plant growth rate with increasing concentrations; however, at a concentration of 25 mg∙L⁻¹, it increased inflorescence biomass and apical inflorescence size. The high-performance liquid chromatograph analysis of major cannabinoids showed no statistically significant differences in total cannabidiol (CBD) and Δ9-tetrahydrocannabinol (Δ9-THC) contents among the treatment groups (25, 50, 100, 200, and 400 mg∙L⁻¹). However, the calculated production of CBD and THC per plant was significantly highest at DIN 25 mg∙L⁻¹. Overall, at a concentration of 25 mg∙L⁻¹, DIN treatment not only decreased the height of female hemp but also enhanced the production of female hemp inflorescences as well as major cannabinoids (CBD and Δ9-THC). Our results indicate that at a concentration of 25 mg∙L⁻¹, DIN is suitable for use in a vertical farming system. However, the Δ9-THC content needs to meet the 0.3% standard for industrial use. These findings can be applied in various fields that use hemp.