Enhancing winter-grown watermelon (Citrullus lanatus) physiological performance, yield and quality through environmental manipulation using heating and supplementary LED lighting strategies

Low temperature, inadequate light intensity and short-day length are the main limiting factors for watermelon (Citrullus lanatus) production during winter. This study investigated the effects of environmental manipulation including temperature, supplementary light and photoperiod extension on the growth, physiology, yield and quality of winter grown watermelon. A completely randomized design was used for the evaluation of five environmental treatments: T0; control, T1; heating, T2; heating + red and blue light, T3; red and blue light and T4; high powerful LED. Supplementary red: blue light ratio was 70:30 from 16.00 to 22.00 and 6.00 to 10.00 with a light intensity of 600 μmol · m⁻² · s⁻¹ and for the high-powerful-LED intensity were 1500 μmol · m⁻² · s⁻¹ from 6.00 to 19.00. The results revealed that among the treatments, T4 showed the best physiological responses and led to early flowering, better anther dehiscence and pollen release and the highest fruit set rate (98%). Fruit yield and quality attributes were significantly improved in T2 and T4 which have the maximum yield per plant (1.59 kg · plant⁻¹), flesh thickness, flesh color and the highest sugar content (12.8 °Brix). Control, on the other hand, yielded smaller, misshapen fruits that were less sweet and less marketable. Hence, it was concluded that regulating the temperature and lighting strategies is essential to optimize the environment which has potential for enhancing the yield and quality of winter watermelon production.