Effect of foliar application of naphthalene acetic acid and plant thinning on sugar contents of melon (Cucumis melo) fruit cv. Khatooni

Abstract Total soluble solid (TSS) content is commercially used as fruit quality index because of its high positive correlation with sugar content. In the present study, The effect of foliar application of naphthalene acetic acid (NAA) with different concentrations (0, 25, 50, and 100 mg.L-1) at 4 true leaf and fruit set stages and plant training (pruning and thinning) on TSS and soluble sugar (i.e. sucrose, glucose and fructose) contents of fruit were evaluated in melon (Cucumis melo L.) cv. Khatooni. Results showed that NAA treatments significantly increased TSS and soluble sugar contents. The highest TSS and soluble sugar contents were observed in 100 mg.L-1 NAA. In contrast, TSS and soluble sugar contents were decreased significantly by plant thinning. In mature fruits, an obvious gradient of TSS and soluble sugar contents was detected, ascending from pedicel to middle and umbilicus part of mesocarp. Also sucrose was dominant sugar in ripening fruit. Results of this work suggest that application of 100 mg.L-1 NAA at fruit set could be used to increase TSS and soluble sugar contents of melon cv. Khatooni.