Lycopene, carbohydrates, ascorbic acid and yield components of diploid and triploid watermelon cultivars are affected by deficit irrigation

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, lycopene content, vitamin C and sugar composition 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', 'RWM 8036', 'Allsweet', 'Sugarlee', and 'SWD 7302' (diploids) and 'Summer Sweet 5244', 'SWT 8706', 'Sugar Time', and 'Tri X Sunrise' (triploids). Total water applied through a subsurface drip system was 395, 298 and 1.73 mm, for the 1.0, 0.75 and 0.50 ET rates, 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 'Tri X Sunrise', 'SWT 8706', and 'SWD 7302'. 'Sugar Time' had the highest soluble solids content (13.4%) of all cultivars (range 9.7-11.0%). Triploid cultivars had firmer flesh compared to diploids (12.0 v 9.9. N). Lycopene content increased slightly with maturity (55.8 to 60.2 mug g(-1) fw), and was significantly higher at 0.75 ET and 1.0 ET. Lycopene content averaged over all treatments was 60-66 mug g(-1) fw for triploids and 45 to 80 mug g(-1) fw for diploid fruits. Overall, lycopene and vitamin C content did not decrease with deficit irrigation at 0.75 ET. There was genetic variability for lycopene, vitamin C, and sugar composition, primarily fructose, among diploids and triploids.