Plant water relations as affected by osmotic potential of the nutrient solution and potential transpiration in tomato (Lycopersicon esculentum Mill.)

The hypothesis that water flow into tomato fruits is affected similarly by osmotic potential of the nutrient solution and potential transpiration (shoot environment) via their effects on stem water potential, was tested through experiments carried out in two glasshouses where climate was controlled to maintain a desired potential transpiration rate (normal and depressed, respectively). This climate treatment was factorially combined with a root zone osmotic potential treatment, whereby two values of osmotic potential were compared in each experiment. Data showed that water uptake per unit leaf area was not affected by osmotic potential of the nutrient solution. The hydraulic resistance within the plant, deduced from measurements of leaf and stem water potential, was independent of the transpiration flow and was not affected by the osmotic potential of the nutrient solution. Water import into the fruit was affected by both treatments and was correlated with the water potential gradient between the stem and the fruit. Since fruit osmotic potential was relatively constant at a given concentration of the nutrient solution, the stem water potential appeared to be a good indicator of fruit growth rate