Responses of some newly developed salt-tolerant genotypes of spring wheat to salt stress: II. Water relations and photosynthetic capacity

Photosynthetic capacity and water relations of two newly developed salt-tolerant genotypes of spring wheat, S24 and S36, were assessed with respect to their parents, LU26S (from Pakistan) and Kharchia (from India). These four lines, together with a salt-tolerant genotype SARC-1 and two salt-sensitive cvs Potohar and Yecora Rojo, were grown until the booting stage in salinized sand culture containing 0, 125 or 250 mol m-3 NaCl in full strength Hoagland’s nutrient solution. S24 and S36 produced significantly greater fresh and dry plant biomass than their parents and the two salt-sensitive lines under saline conditions. There was no consistent relationship between growth and assimilation rate of all cultivars differing in degree of salt tolerance. Stomatal conductance was reduced due to salt stress in all cultivars except Yecora Rojo. The newly evolved genotypes showed relatively higher stomatal conductance than the other cultivars at the highest salt treatment, but there was no consistent relationship between assimilation rate and stomatal conductance. Transpiration in all cultivars reduced consistently with increase in salt concentration of the growth medium, but S36 and S24 had higher transpiration than that of the other lines. The higher transpiration rate in S24 and S36 resulted in lowering their water use efficiency compared with the other cultivars. Water potential and turgor potential of only the two salt-sensitive cultivars, Potohar and Yecora Rojo, were significantly lower than those of the other lines, which themselves did not differ. The physiological traits, such as assimilation rate and water-use efficiency, did not prove conducive to discriminate high salt-tolerant and low salt-tolerant lines examined in this study.