AbstractBACKGROUND: The Mediterranean region suffers water deficit that affects fruit yield and quality. Grafting improves crop tolerance to disease and drought, but the taste and quality of fruit may be negatively affected. The aim of the present work was to determine the quality parameters of mini‐watermelon, ungrafted or grafted onto a squash hybrid rootstock, and grown under different irrigation regimes: 1.0, 0.75, and 0.5 of evapotranspiration (ET) rates.RESULTS: The interaction between grafting and irrigation rate was not significant for the variables tested. The highest fruit yields were recorded at 1.0 ET and at 0.75 ET with respect to 0.5 ET, and they were obtained in grafted plants. Fruit quality was slightly affected by drought, with an increase in K, Mg and spermine concentrations, especially with 0.5 ET. Nitrate concentration in the watermelon pulp was very low (average 10 mg kg−1 fresh weight). Fruit quality parameters were similar in grafted and ungrafted plants, whereas the titratable acidity (TA), juice electrical conductivity, TSS/TA ratio, K and Mg concentrations were improved in the grafted one. Lycopene, dehydroascorbate (DAscA) and total vitamin C contents for grafted plants were higher by 40.5%, 13% and 7.3%, respectively, than those from ungrafted plants. Spermidine and putrescine concentrations were reduced by grafting (by 24% and 59%, respectively).CONCLUSION: Grafting of mini‐watermelon under irrigation deficit did not modify crop response to water availability, but increased productivity and induced small positive changes in plant quality and nutritional value. Copyright © 2008 Society of Chemical Industry