An irrigation experiment using saline-sodic waters was carried out in 2004 in the Volturno river plain (southern Italy) to investigate the growth of the melon cultivar Tendral under saline-sodic conditions. Four salinity irrigation treatments (C, T0.5, T1 and T2) were tested using water with electrical conductivities of 0.9, 8.7, 15.3 and 28.2 dS m-1, respectively. At the end of the crop cycle the electrical conductivity () of the saturated paste in the soil profile between 0.0 and 0.9 m reached values of 0.9, 3.2 4.2 and 6.6 dS m-1, respectively, for the C, T0.5, T1 and T2 treatments. Increasing salinity led to a rise in specific leaf area (SLA; cm2 g-1) while it reduced leaf area (LA, m2 per plant), leaf area ratio (LAR, cm2 g-1), the unit leaf rate (ULR, g m-2 per day) and water use efficiency (WUE g kg-1). The relative growth rate (RGR, g g-1 per day) and the biomass produced (W, g plant-1) decreased. The reduction in RGR was closely related to the reduction in relative leaf area growth rate (RLAGR, cm2 of leaf cm-2 per day), the relative leaf weight growth rate (RLWGR, g of leaf g-1 per day) and the relative fruit weight growth rate (RFWGR, g of fruit g-1 per day). A highly significant positive correlation was found between RGR and LAR (R2 = 0.9847***), while between RGR and ULR the determination coefficient was also significant but lower (R2 = 0.6808***). The most visible effect of the salinity treatment was on LA reduction. In T0.5, T1 and T2 the LA was respectively 10%, 34% and 45% less than in the C treatment. W and the crop evapotranspiration (ETc) also decreased with increasing salinity. The reduction in W for T0.5, T1 and T2 (respectively, 2%, 28% and 40% less than treatment C) was greater than the reduction in ETc (respectively, 2%, 22% and 32% less than treatment C). Therefore also the WUE significantly decreased as salinity increased. The Tendral cv. responded to salinity mainly with morphological adaptations, first with a LA reduction that was followed by decreases in the W and ETc. There may well also be functional adaptations associated with ULR reduction.
