Lycopene is the main health-giving constituent of tomatoes and its concentration can be enhanced by increasing the salinity of the nutrient solution supplied to the roots.
The research reported here examined the effect of changing the electrical conductivity of the nutrient solution when the fruit were at different stages of development.
The truss tomato 'Durinta' was grown hydroponically in a polythene greenhouse. After 14 weeks, one truss with at least four flowers was selected for monitoring on each plant. The electrical conductivity of the nutrient solution was then raised from 2.3 to 4.5 dS m-1 when those flowers reached anthesis. With other plants, the conductivity was either raised four weeks after anthesis or not at all. Final fruit weight was unaffected by changing the solution's conductivity but the concentration of sugars was increased in red ripe fruit.
The effect on sugar concentration was less if the conductivity increase was delayed. The lycopene concentration in fruit increased as they ripened and was markedly increased by both of the high conductivity treatments. As the lycopene concentration was unaffected by the timing of the increase in conductivity, the results suggest it may also be enhanced by quite short exposures to high conductivity.
Effects of High Electrical Conductivity of Nutrient Solution and its Application Timing on Lycopene, Chlorophyll and Sugar Concentrations of Hydroponic Tomatoes during Ripening by Wu and Kubota (2008). Scientia Horticulturae 116: 122-129. The contents of issues of Scientia Horticulturae and abstracts of papers are provided at www.elsevier.com/locate/scihorti.