GROWTH, FRUIT YIELD, AND ION CONCENTRATION IN TOMATO GENOTYPES AFTER PREEMERGENCE AND POSTEMERGENCE SALT TREATMENTS

The effects of increasing salinity on dry weight and ion concentration of shoots at various growth stages and on fruit yield in four tomato (Lycopersicon esculentum Mill.) genotypes were assessed. The salt trea tments (35, 70, and 140 mM NaCl) were applied pre-emergence (seed sowi ng) (pre-E) and post-emergence (four-leaf stage) (post-E) and maintain ed during plant growth. Genotype salt tolerance, measured as shoot dry weight in response to increases in salt concentration, varied dependi ng on plant growth stage and salt application time. When salt was appl ied pre-E, salt tolerance increased with plant age, whereas when appli ed post-E, 45-day-old plants were the most salt tolerant. Mature plant s were similarly salt tolerant independent of the growth stage at whic h the salt treatments began. However, fruit yield of all genotypes was higher when salt was applied pre-E than post-E. Shoot dry weight decr eased as shoot Cl and Na ion concentrations increased. During early gr owth stages, pre-E salt-treated plants had the highest Cl- and Na+ con centrations and the lowest shoot dry weights. However, at the advanced stages, shoot Cl- and Na+ concentrations were equal for both salt app lication times. These results show that the plants must adapt to salin ity during a period that allows them to develop a mechanism to regulat e internal Cl- and Na+ concentrations and, thus, grow under high salin ity.