Deficit irrigation influences yield and lycopene content of diploid and triploid watermelon

Abstract

Many vegetable production regions in the southwestern US are strictly regulated on water use. In addition, demand for high quality and nutritious vegetables has increased. This study was performed to explore the effects of deficit irrigation on yield, fruit quality and lycopene content of red-fleshed diploid and triploid watermelon (Citrullus lanatus (Thunb) Matsum & Nakai) cultivars. Irrigation treatments were 1.0, 0.75 and 0.5 evapotranspiration (ET) rates. Cultivars used were ‘Summer Flavor 710’, ‘RWW 8036’, ‘Allsweet’, ‘Sugarlee’, and ‘SWD 7302’ (diploids) and ‘Summer Sweet 5244’, ‘SWT 8706’, ‘Sugar Time’, and ‘Tri-XSunrise’ (triploids). Total water applied through a subsurface drip system was 395, 298 and 173 mm, for the 1.0, 0.75 and 0.50 ET, respectively. Total yields were highest at 1.0 ET (53.9 t ha-1) compared with 0.5 ET (26.8 t ha-1). Triploids had a 34% higher total yield and fewer culls (2%) compared with diploid cultivars (25%). Highest yields were obtained for ‘Sunrise’, ‘SWT 8706’, and ‘SWD 7302’. Highest soluble solid content was measured for ‘Sugar Time’ (13.4%) and was significantly higher than other cultivars (range 9.7-11.0 %). Triploid cultivars had more firm flesh, compared with diploids (12.0 vs. 9.9 N). Lycopene content increased slightly with maturity (55.8 to 60.2 :g g-1 fw), and was significantly higher at 0.75 ET than 1.0 ET in melons at ripe and overripe maturity stages. Lycopene content averaged over all treatments was 60-66 :g g-1 fw for triploids and 45 to 80 μg g-1 fw for diploid fruit.