Tomato salt tolerance: impact of grafting and water composition on yield and ion relations

We evaluated the salt tolerance of tomato cv Big Dena under both nongrafted conditions and when grafted on Maxifort rootstock, under a series of 5 salinity levels and 2 irrigation water composition types. The salinity levels of the irrigation water were -0.03, -0.15, -0.30, -0.45, and -0.60 MPa osmotic pressure (corresponding to specific electrical conductivity values of 1.2, 4.0, 8.5, 12, and 15.8 dS m(-1), respectively). We salinized the irrigation water with either a mixture of salts with a predominant composition consisting of Na+-Ca2+-Cl- salts, a composition typical of coastal Mediterranean ground waters or, alternatively, a salt composition that was of mixed Na+-Ca2+-SO42- -Cl- ions, a water composition more typical of interior continental basin ground waters such as those of the California Central Valley in the US. We determined that there were no statistically significant differences in tomato salt tolerance (fruit yield) relative to water type. This result indicates that in the range of Cl-concentrations tested in our experiment (up to 150 mmol L-1), Cl- is not an important factor in tomato yield reduction associated with salinity. The grafted Big Dena on Maxifort tomato plants exhibited increased yield both under control and elevated salinity levels relative to the nongrafted Big Dena plants. In contrast to absolute yield relationships, expression of salt tolerance in terms of relative yield, as salt tolerance is commonly expressed, provides the conclusion that grafted Big Dena on Maxifort tomato plants are slightly less salt tolerant than nongrafted Big Dena plants. Our data also indicate that, for tomato, decreased yield under saline conditions is well related to increased leaf Na+ concentrations.