Tomato quality is more dependent on temperature than on photosynthetically active radiation

BACKGROUND: A greenhouse experiment was performed to study the effect of cumulative air temperature and photosynthetically active radiation (PAR) on tomato quality. Tomato plants were subjected to two different shading treatments causing a 30 and 50% reduction in incoming PAR respectively (plants were exposed to 70 and 50% of incoming PAR respectively). Control plants (exposed to 100% of incoming PAR) were also included in the experiment. The experiment was carried out under unheated greenhouse conditions. To minimise the dependence of temperature on PAR, only a small area inside a large greenhouse was shaded, thereby allowing air currents to homogenise temperature all over the enclosure. Parameters of tomato quality were correlated with cumulative temperature (Tcum) and cumulative PAR (PARcum) for a period of 45 days before harvest. RESULTS: Tcum was strongly correlated with firmness, electrical conductivity, soluble solids content and total phenolic compounds and weakly correlated with pH, dry weight, titratable acidity and vitamin C content. PARcum was only weakly correlated with firmness, dry weight, soluble solids content and total phenolic compounds. CONCLUSION: Tcum has a stronger influence on tomato quality than PARcum. Growers could obtain tomatoes of similar quality under lower PAR than that provided by natural sunlight.