Effects of Root Temperature and Cluster Position on Fruit Quality of Two Cocktail Tomato Cultivars

Managing root temperature can strongly influence plant growth in various species. Our previous work has shown that a positive effect of root cooling on the nutritional quality (sugars, vitamin C, and carotenoids levels) of two cocktail tomato cultivars, while the yield and mineral content was moderately reduced in two seasons. But few studies have investigated which cluster quality is more influenced by root temperature. The main purpose of this study was to evaluate the effects of root temperature and different cluster positions (the first to the fourth clusters) on fruit quality parameters of two cocktail tomato cultivars (&lsquo:Amoroso&rsquo: and &lsquo:Delioso&rsquo:). Two root temperatures, cool (10 &deg:C) and control (18&ndash:22 &deg:C), were applied to the roots of hydroponically cultivated tomato plants after inflorescence until the final harvest in the greenhouse. The results showed that root cooling has no influence on the biomass of fruits (both dry weight and fresh weight) of all clusters, but it increased the sugar (6.1&ndash:8.4%) and vitamin C (9.1&ndash:12.5%) concentration of the second cluster of &lsquo:Amoroso&rsquo: and the third cluster of &lsquo:Delioso&rsquo: compared to the control. In most cases, significant positive changes (8&ndash:23.8%) in the levels of lycopene were observed in response to low root temperature treatment, but the effect was dependent on different cluster positions and different cultivars. Most mineral element levels showed no response to the root temperature. Significant reductions (10% and 17.6%) along with the root cooling was only found in the level of zinc and potassium of the first and the second cluster of &lsquo:Delioso&rsquo:, respectively. It was concluded that the fruits from the second or third clusters containing more sugars, vitamin C, and lycopene, were more influenced by root cooling. In addition, the effect of cluster position on fruit quality was different between two root temperature groups. Root cooling reduced the heterogeneity in fruit quality parameters among the clusters of &lsquo:Amoroso&rsquo: and increased the differences in &lsquo:Delioso&rsquo:.