Grafting Rootstock, Scion, and Field Holding Effects on Seedless Watermelon Fruit Quality

Watermelon is a good source of vitamin C and contains the antioxidants and anti inflammatory compounds citrulline and lycopene.  Quality of watermelon fruit is a combination of firmness, full red color, sweetness, and perceived shelf life in field and market, and fresh cut watermelon also needs low drip loss.   Watermelon grafting is widely used outside of the United States to avoid soil borne pathogens and abiotic stresses.  Commonly used rootstocks and seedless watermelon scions were used to determine best fruit productivity and marketable yield in the southeastern United States relative to non-grafted plants.  Fruit identified as ripe were left in the field on vine 0 to 2 weeks to test the relative hold life, then used for fresh cut studies to determine firmness and drip loss.  Interspecific squash hybrid rootstocks ‘Carnivor’ and ‘Super Shintosa’ resulted in highest yields for most of the scions, with yield increases of 20% to 80% relative to non-grafted watermelons.  Of the scions tested, ‘Fascination’ and ‘Sugar red’ had best yields in 2012 compared to ‘Trix313’, ‘Sugar Heart’, and ‘Sugar Coat’.   Lycopene content increased slightly (up to 10%), depending on cultivar, with grafting while citrulline content decreased 10% with grafting.  Holding fruit in the field for 1–2 weeks increased lycopene content from 50 to 65 mg/kg and pH from 5.4 to 5.8.  Firmness was increased 10% to 40% by grafting and held up as fresh cut product, but fruit harvested after 2 weeks in the field were below acceptable firmness after fresh cut storage. Total soluble solids were relatively unchanged by rootstock or holding system. The percentage of drip loss of fresh cut product was reduced by 50% to 100% using grafted watermelons regardless of fruit holding time in field.  Citrulline content was stable across holding time, ranging from 2.5 to 4.5 g/kg.  Our results indicate that grafted watermelon can improve firmness and reduce drip loss in fresh cut watermelon without loss of sugars or lycopene, and can help extend field shelf life by a week compared to non-grafted watermelons.