Experimental Control of Day and Night Temperatures to Improve the Growth and External Quality of Salvia miltiorrhiza Bunge

Abstract

Salvia miltiorrhiza is a medicinal crop belonging to the Lamiaceae family. It is commonly used in China as an ingredient in health-promoting teas that enhance immunity and prevent diseases. Although some Korean local farmers have reported that S. miltiorrhiza grows vigorously in high temperatures and produces roots with a deep red color, there is no clear evidence or literature to confirm this. Therefore, this study investigated the growth and external quality of S. miltiorrhiza in response to different day and night temperature levels. Day and night temperature treatments were designed into four levels: 20/15, 24/19, 28/23, and 32/27°C, respectively. Among the parameters related to plant sizes, the shoot height and number of roots showed the highest values in the 32/27°C treatment, while other parameters, particularly the shoot width and root length exhibited the highest values in the 28/23°C treatment. In contrast, the majority of parameters, including the fresh weight and dry weight, which are indicative of root biomass, were lowest in the 20/15°C treatment, suggesting that S. miltiorrhiza, a species that prefers relatively high temperatures, thrives in warmer conditions. Importantly, the root fresh and dry weights, which are likely to be correlated with the market value of S. miltiorrhiza, showed the same significance levels within the temperature range of 24/19 -32/27°C, but not in the relatively low-temperature treatment of 20/15°C. Thus, cultivation of S. miltiorrhiza is deemed feasible within all temperature ranges except for 20/15°C, with optimal conditions falling within the temperature range of 24/19-32/27°C. The CIELAB a * value, associated with red color, was highest in the comprehensive assessment of the 32/27°C treatment. Moreover, in the 32/27°C treatment, the Royal Horticultural Society (RHS) color chart values were found to indicate a deep reddish or brown-red color, with readings of 166B and 174A. Additionally, the root color obtained the highest visual score in the 32/27°C treatment. Based on previous studies, a * is considered to be related to the content and quantities of tanshinones and other hydrophilic