Journal of the Science of Food and Agriculture J Sci Food Agric (2008) Fruit quality of mini-watermelon as affected by grafting and irrigation regimes Simona Proietti, 1 Youssef Rouphael, 2 Giuseppe Colla, 2 Mariateresa Cardarelli, 2 Marina De Agazio, 3 Massimo Zacchini, 3 Elvira Rea, 4 Stefano Moscatello 1 and Alberto Battistelli 1∗ 1 Istituto di Biologia Agroambientale e Forestale, Consiglio Nazionale delle Ricerche, Viale Marconi 2, 05010 Porano (TR), Italy 2 Dipartimento Geologia e Ingegneria Meccanica, Naturalistica e Idraulica per il Territorio, Universit ` a degli Studi della Tuscia, Via S. Camillo de Lellis snc, 01100 Viterbo (VT), Italy 3 Istituto di Biologia Agroambientale e Forestale, Consiglio Nazionale delle Ricerche, Via Salaria km 29.300, 00016 Monterotondo Scalo (Roma), Italy 4 Istituto Sperimentale per la Nutrizione delle Piante, Consiglio per la Ricerca e la Sperimentazione in Agricoltura, Via della Navicella 2/4, 00184 Roma, Italy Abstract BACKGROUND: 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.  2008 Society of Chemical Industry Keywords: Citrullus lanatus; grafting; lycopene; vitamin C; water stress INTRODUCTION Watermelon (Citrullus lanatus (Thunb.) Matsum. and Nakai) is one of the most economically important and widely cultivated vegetable crops in Italy and in the Mediterranean region. In this area water availability is a serious problem for agriculture management and requires the use of effective irrigation strategies for crop yield and fruit quality. Limited water availability causes large yield losses for all crop plants, inducing important physiological and biochemical changes. When water supply is limited, plant structure is modified by increasing the root:shoot ratio. 1,2 Limitation of leaf growth and increased stomatal resistance to gas exchanges are associated with a decrease of water and mineral flow from roots, a reduction of photosynthesis and a decrease of carbohydrate production and partitioning toward the shoot organs of the plant including fruits. 1,3 Traditional breeding programmes and genetic trans- formation of plants could be applied to develop new cultivars resistant to drought. However, commercial success has been very limited due to the genetic and ∗ Correspondence to: Alberto Battistelli, Istituto di Biologia Agroambientale e Forestale, Consiglio Nazionale delle Ricerche, Viale Marconi 2, 05010 Porano (TR), Italy E-mail: alberto.battistelli@ibaf.cnr.it Contract/grant sponsor: Lazio Region (Received 1 August 2007; revised version received 23 November 2007; accepted 14 December 2007) DOI: 10.1002/jsfa.3207  2008 Society of Chemical Industry. J Sci Food Agric 0022–5142/2008/$30.00