Growth, Fruit Yield, and Ion Concentration in Tomato Genotypes after Pre- and Post-emergence Salt Treatments

Additional index words. growth stage, Lycopersicon esculentum, NaCl tolerance, shoot Cl, Na and K ion concentrations Abstract. 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 treatments (35, 70, and 140 mM NaCl) were applied pre-emergence (seed sowing) (pre-E) and post-emergence (four-leaf stage) (post-E) and maintained during plant growth. Genotype salt tolerance, measured as shoot dry weight in response to increases in salt concentration, varied depending on plant growth stage and salt application time. When salt was applied pre-E, salt tolerance increased with plant age, whereas when applied post-E, 45-day-old plants were the most salt tolerant. Mature plants were similarly salt tolerant independent of the growth stage at which the salt treatments began. However, fruit yield of all genotypes was higher when salt was applied pre-E than post-E. Shoot dry weight decreased as shoot Cl and Na ion concentrations increased. During early growth stages, pre-E salt-treated plants had the highest Cl-and Na + concentrations and the lowest shoot dry weights. However, at the advanced stages, shoot Cl- and Na + Concentrations were equal for both salt application times. These results show that the plants must adapt to salinity during a period that allows them to develop a mechanism to regulate internal Cl- and Na+ concentrations and, thus, grow under high salinity. Salt tolerance is a complex trait. Breeders developing crops tolerant to saline soils have found few traits that can be used as markers for reliably assessing salt tolerance. In theory, phenotypic markers for salt tolerance should be easy to measure and should be expressed during seed germination, at the seedling stage, or at advanced growth stages. However, the plant's response to salinity can vary with growth stage (Shannon, 1985). Some have argued that, in certain crops, selecting for salt tolerance at the early growth stages may not correlate with the crop's tolerance at later growth stages (Ashraf and McNeilly, 1988; Kingsbury and Epstein, 1984). In many salinity studies, one harvest date has been used to correlate growth with the physiological responses to salinity. The results from such studies can be misleading when genotypes, species, or salinity treatments are compared (Hunt, 1982). Generally, salt tolerance in tomato has been evaluated only at germination (Jones, 1986), during early plant development (Guerrier, 1984), or at maturation (Bolarin et al., 1991). However, some authors have reported that the salt tolerance of young tomato plants did not correlate highly with that of mature plants (Norlyn and Epstein, 1984; Shannon et al., 1987). Furthermore, Caro et al. (1991) pointed out that the ranking of salt-tolerant tomato geno- types based on vegetative characteristics in mature plants may differ from a ranking based on fruit yield. We report the effects of increasing salinity at pre-emergence (pre-E) and post-emergence (post-E) on growth and ion concentra- tions of tomato plants at several growth stages and on fruit yield and its relationship to shoot dry weight, with the objective of defining patterns of variation in the response to salinity shown by 30, 45, 100, and 180-day-old plants.