Increasing salt tolerance in tomato and lettuce by inducing plant adaptation:: Haloconditioning

The use of irrigation water with high soluble salts content greatly decreases crop yield. Some strategies could be used to increase agronomical crop salt tolerance by inducing plant adaptation under salinity. This is based on the fact that all plants apparently have the neccessary genetic information to adapt to salinity to some extent and it is mainly supported by the spectacular results reported with glycophytic cell lines. The method of haloconditioning basically consists of inducing adaptation mechanisms of salt-tolerance by putting different plant organs into contact with the stressful agent through the complete immersion of the whole plant in solutions containing NaCl, PEG or a mixture of both, in a controlled dosis and time. Preliminary experiments revealed the viability of this approach when 6 to 16 day-old tomato plants were able to live and grow after the complete immersion in a low osmotic potential solution (-1 MPa) during a period of up to 3 days. More recent experiments on tomato and lettuce have shown that some haloconditioning treatments applied at seedling level induce greater vegetative growth and fruit yield under salinity, as well as adaptive physiological responses concerning ionic, nutritional, osmotic and metabolic regulation. Morphological alterations observed during the early plant development and differential expression of some proteins in adult plants support the idea that changes at genetic level occur. The efficiency of the method seems to depend on the quantity and quality of the adaptive responses induced. A compendium of interesting results obtained to date with this method is presented.