Increase in Total Soluble Solids Content in Tomato Fruits by Applying Water Stress in High Density-Low Truss Cultivation

Abstract

This study was conducted to increase sugar content in tomato fruits by applying water stress in high density-low truss cultivation. In the first chapter, the change in total soluble solids content (TSS) in fruits as affected by high electrical conductivity (EC) levels up to 13.7 dS m-1 of nutrient solution at different growth stages and incidence of blossom-end rot (BER) as affected by salt stress intensity and growing seasons were investigated. Growth of tomato plants was inhibited and fruit yield decreased, while soluble sugar content in fruits increased as EC of nutrient solution increased. The sugar content of tomato fruits cultivated in summer season was higher than that cultivated in winter season. BER incidence was less in winter cultivation. In the second chapter, the change in fruit quality as affected by combination of salt stress and root zone restriction was investigated to reduce the negative side effects of high EC treatment such as growth inhibition, yield loss, and higher incidence of BER. Growth and yield decreased as EC level increased and root zone volume decreased. TSS, titratable acid, and ascorbic acid in fruits increased as the root zone volume decreased. TSS increased in higher EC treatment (≥ 4.2 dS m-1) and TA remarkably increased in the EC treatment of 7.0 dS m-1 those combined with the severe root zone restriction (container size S treatments). Glucose, fructose, citric acid, and ascorbic acid contents in tomato fruits as affected by EC level and root zone restriction were most significant when the treatments was applied at the fruit-ripening stage. Results imply that TSS in tomato fruits increased as EC levels increased and the effect is more significant when the high EC treatment is applied at the earlier stages. Fruit quality could be improved with minimized yield reduction and incidence of BER if the high EC treatment was combined with root zone restriction treatment. Cultivating tomato plants using a 200 mL-container with application of high-EC nutrient solution will be feasible for high density-low truss cultivation of high quality tomato fruits.