Effect of NaCl priming on increased salt tolerance in tomato

Tomato seeds (Lycopersicon esculentum Mill.) cvs Pera, Muchamiel, P-73 and GC-72, were primed with 0,0.5 and 1.0 M NaCl solutions. The plants were then grown at 35,70 and 140 mM NaCl. These salt treatments were applied pre-emergence (seed sowing) and post-emergence (4 leaf stage). The effect of seed priming on yield was different depending on both the NaCl concentration used for seed priming and on the time of starting the salt treatments during the growing period of the plants. The yield increase under 1.0 M NaCl priming was mainly due to increased fruit weight, but was always reduced by increasing the NaCl treatment (35-140 mM). The effect of this seed priming on yield was higher when salt treatments were applied pre- rather than post-emergence, although it was significant only in plants treated at 35 and 70 mM NaCl. At pre-emergence, the yield increased in cvs Pera, Muchamiel and GC-72, whereas at post-emergence only cv. GC-72 increased its yield by salt priming. The increase in yield of cv. GC-72 was associated with a tendency to decrease the shoot Cl and Na ion contents and a tendency to increase the K/Na ratio. Both at pre- and post-emergence stages, the relationships between yield and K/Na ratio were highly significant (P = 0.001) with no significant differences between the slopes.