Allyl-isothiocyanate Content and Physiological Responses of Wasabia japonica Matusum as Affected by Different EC Levels in Hydroponics

This study aimed to determine the effect of EC (electrical conductivity) levels of nutrient solution in hydroponic culture on allyl-isothiocyanate (AITC) content within plant tissues, Vitamin C content and physiological responses in wasabi plant (Wasabia japonica M. ‘Darma’). The ‘Darma’ was grown for 5 weeks with a deep flow technique (DFT) system controlled at 5 different EC levels, including 0.5, 1, 2, 3, and 5 dSㆍm-¹. In result, the highest total content of AITC showed at EC level 5 and 3 dSㆍm-¹ for 1 or 5- week, respectively. The total content of AITC increased about 1.2-1.4 times when the plants were grown in the EC levels between 0.5 and 2 dSㆍm-¹, whereas the content decreased about 6 and 56 % in the EC level 3 and 5 dSㆍm-¹, respectively. The content of AITC was relatively higher in petiole tissue, about 53 %, taken from 1 week-grown plants when the EC was controlled between 0.5 and 2 dSㆍm-¹. Root tissue also had relatively higher content of AITC, about 45.1 %, when the EC was controlled at 3 and 5 dSㆍm-¹. However, a 5-fold decrease in the AITC content was found in blade tissue and a 6.8-fold decrease in root when the EC was controlled at 5 dSㆍm-¹ for 5 weeks. There was no significant difference in the vitamin C content in 1-week grown leaf tissues under the different EC level treatments; but, the content increased about 27% in 5-week grown plants at the EC level between 0.5 and 2 dSㆍm-¹, compared to the 1 week-grown leaf tissue. Electrolyte leakage of leaf tissue taken from 3-week grown plant was 3-fold higher at the EC level 5 dSㆍm-¹, compared to the EC level between 0.5 and 2 dSㆍm-¹. Chlorophyll content, photosynthesis rate and transpiration rate were decreased when the EC was controlled at higher than 2 dSㆍm-¹. Leaf water content, specific leaf area and growth were decreased when the EC was controlled at 5 dSㆍm-¹ for 5 weeks. All the integrated results in this study suggest that the EC level of nutrient solution should be maintained at lower than 3 dSㆍm-¹ in order to improve nutritional value and quantity required for hydroponically grown wasabi as functional vegetable.