Abstract
Water and salinity stresses have been applied to improve the tomato fruit quality. To produce high-quality tomato fruit, the effect of stresses on chemical contents and physiological response must be known. We examined the chemical contents (sugar, organic acid, amino acid and inorganic ions) and osmotic potentials of tomato fruit (Lycopersicon esculentum Mill.) grown under water stress and salinity stress. For the two water stress treatments, the irrigation water amounts were fixed at 50% of the control (13% of soil water content), and 25% of the control. For salinity stress, the concentration of irrigation water was adjusted by mixing additional fertilizer, until it had the 2.5-fold electric conductivity of control (1.6 dSmu-1). Comparing both stresses, which had similar levels of leaf water potential, sugar and organic acid contents on a fresh weight basis were enhanced by the salinity stress, but not by the water stress. Amino acid contents on a fresh weight basis, except for proline and γ-aminobutylic acid, were not affected for water stress, while most of the amino acid contents for the salinity stress were higher than those for the control. The high contents of amino acids could not be caused by the concentration effects such as sugar and organic acid. Furthermore, the mechanisms of osmotic adjustment were different between both stresses. We conclude that the changes in chemical contents and the physiological responses were different between both stresses, and that the use of the salinity stress was more efficient rather than the use of the water stress to produce a high quality tomato fruit.
