Effect of salinity on yield, fruit quality, leaf gas exchange, and mineral composition of grafted watermelon plants

A greenhouse experiment was carried out to determine growth, yield, fruit quality, gas exchange and mineral composition of watermelon plants (Citrullus Lanatus L. 'Tex'), either ungrafted or grafted onto two commercial rootstocks 'Macis' [Lagenaria siceraria (Mol.) Standl.] and 'Ercole' (Cucurbita maxima Duchesne x Cucurbita moschata Duchesne) and cultured in NFT. Plants were supplied with a nutrient solution having an electrical conductivity (EC) of 2.0 or 5.2 dS(.)m(-1). The saline nutrient solution had the same basic composition, plus an additional of 29 mm of NaCl. Increased salinity in the nutrient solution decreased total yield. The reduction in total yield in saline treatments compared to control was due to a reduction in the fruit mean mass and not to the number of fruit per plant. Total fruit yield was 81% higher in grafted than in ungrafted plants. The lowest marketable yield recorded on ungrafted plants was associated with a reduction in both fruit mean mass and the number of fruits per plant in comparison to grafted plants. Salinity improved fruit quality in all grafting combinations by increasing dry matter (DM), glucose, fructose, sucrose, and total soluble solid (TSS) content. Nutritional qualities of grafted watermelons such as fruit DM, glucose, fructose, sucrose, and TSS content were similar in comparison to those of ungrafted plant. In all grafting combinations, negative correlations were recorded between Na+ and Cl- in the leaf tissue and net assimilation of CO, Grafting reduced concentrations of sodium, but not chloride, in leaves. However, the sensitivity to salinity was similar between grafted and ungrafted plants and the higher total yield from grafting plants was mainly due to grafting per se.