NaCl pre-treatment at the seedling stage enhances fruit yield of tomato plants irrigated with salt water

Although salt-adaptation seems to be a widespread property of plants, the adaptive response has been rarely differentiated to the tolerance response. We report on the adaptive response of tomato plants to growing under saline conditions following a 15 day pre-treatment with a lower NaCl concentration (half) than that used during the plant growth. After 20 days of salt treatment (100 mM NaCl), the biomass of the adapted plants increased significantly with respect to that of the unadapted plants when the pre-treatment was applied to five leaf seedlings, but not at the two leaf stage. The long-term adaptive response was determined in two tomato genotypes with different tolerance to moderate salt levels. At 70 mM NaCl, the adapted-plants of the more salt-sensitive genotype produced up to 29% more fruit yield than did the unadapted plants. However, no positive effect was observed to long-term in the adapted-plants of the more salt-tolerant genotype, which suggests that the stress level necessary to trigger the adaptive response is related to the tolerance degree of genotype. The physiological response of the plants showing a positive response to the adaptation was also modified to long-term. Thus, K⁺ concentrations increased in the young leaves of the adapted plants, with respect to unadapted plants, and moreover these differences increased with the salinization period. These results indicate that the changes in growth and physiological responses induced by NaCl pre-treatment at the seedling stage are maintained throughout plant life cycle and this is, therefore, an interesting strategy for increasing the salt tolerance in tomato plants.