Abstract The effect of different levels of root zone temperature (RZT) and electrical conductivity (EC) of nutrient solution on lycopene, β-carotene, chlorophyll concentration and tomato quality (TSS, TA and TSS/TA ratio) of tomato plants grown under greenhouse conditions were determined. Tomato plants were irrigated with various EC (0, 1.5, 3 and 6 ds.m -1) via pumps connected to 4 sets of water tanks and RZT (20, 25 and 30 C) regulated via electrical heater in each experimental unit. All the plants were supplied with a mixture of nutrient solution containing all essential elements. Lycopene, β-carotene and chlorophyll concentration of fruits measured at yellow and red ripening stages, but TSS, TA and TSS/TA measured at the end of fruit harvest time. The results showed that TSS and TA contents of red ripe tomato fruits grown in high EC treatment were significantly greater than those grown in low EC treatment. Furthermore, RZT 30 o C had a significant effect on TSS content in comparison with RZT 25 oC, while for TA trait, a significantly greater effect was observed by RZT 25 than that of RZT 30o C. High EC treatment enhanced lycopene concentrations of fruits at red and yellow ripening stages compared to low EC treatment. Based on the results, EC treatment showed no significant effect on βcarotene concentration at the yellow stage, while it started to increase in high EC of 6 ds.m at the red stage. Besides, our results showed that RZT did not significantly affect lycopene and β-carotene concentrations at the two ripening stages. Chlorophyll a concentration in fruit decreased in high EC treatment compared with low EC (control) at both red and yellow stages. RZT had a significant impact on chlorophyll a at yellow but not red stage. The highest amount of chlorophyll a was seen in RZT 20 o C compared with RZT 30 amount. Regarding chlorophyll b, no significant effect was observed by EC treatments at both yellow and red stages, Moreover, RZT had a significant effect on chlorophyll b content at yellow but not red stage, so that a significant decrease was observed in high RZT.

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