Early cell enlargement by night-time heating of fruit produce watermelon fruit (Citrullus lanatus Matsum. et Nakai) with high sucrose content

To investigate the effects of night-time temperature on cell and fruit size, and sugar accumulation in watermelon fruit, fruits were treated with high night-time temperatures in a greenhouse. The minimum night-time ambient temperature of the heating box (18 °C) was approximately 6 °C higher than that of the control. The length, diameter and weight of heat-treated fruit at the end of heating treatment, 16 days after anthesis (DAA), were significantly greater than that of control fruit, but those at harvesting, 42 DAA, were almost the same in both treatments. Mean cell size of the outer portion of heat-treated fruit at 16 DAA was significantly larger than that of the control. Cell size of the fruits at 42 DAA did not differ between heat-treated and control fruits. Sucrose, glucose and fructose content of fruit at 16 DAA did not differ between heat-treated and control fruit. However, sucrose content of the outer portion of heat-treated fruit was 162% of that of control fruit at 42 DAA. Glucose and fructose contents at 42 DAA did not differ between heat-treated and control fruit, except glucose content of outer portion.