NMR-based fruit metabonomic analysis of watermelon grafted onto different rootstocks under two potassium levels

Grafting watermelon onto nonself-rootstock is an effective way to solve the soilborne disease, and potassium plays an important role in fruit quality; however, a comprehensive metabonomic analysis of rootstock on the fruit quality of watermelon under different potassium levels is lacking. In this study, the NMR-based metabonomic approaches was used to reveal the effects of nonself-rootstocks (wild watermelon, bottle gourd, pumpkin) on the fruit metabolites accumulation of watermelon under two potassium levels (normal potassium: 6.0 mM K, low potassium: 0.1 mM K) at ripening stage. Thirty eight metabolites were identified, including nineteen amino acids and ammonium compounds, four organic acids, six sugars, four nucleic acid and five other compounds. Compared with self-grafted plants, nonself-rootstock grafting significantly increased the concentrations of some health-related compounds in watermelon fruit under normal potassium, such as citrulline, methionine, isoleucine, phenylalanine, leucine and valine. Low potassium decreased sucrose concentration, but increased the concentrations of some important fruit metabolites, including citrulline and glucose in watermelon fruit. Nonself-rootstock grafting increased the sucrose and citrulline concentrations under low potassium. Our results suggested that the accumulation of some fruit quality-related compounds in watermelon can be enhanced by grafting onto nonself-rootstocks under both normal and low potassium conditions.