Assessment of Variability in Intrinsic Mesophyll and Carboxylation Efficiencies in Wheat (Triticum Aestivum L.) for Salt Tolerance

Improving the salt tolerance of wheat requires access to genetic diversity and efficient techniques. Genetic progress in increasing yield potential is closely associated with increased photosynthetic activity. To assess the performance of 14 wheat varieties under different saline water irrigation treatments comprising canal water taken as contol (EC of 0.4 dSm⁻¹), EC of 5.0 and 7.5 dSm⁻¹, an experiment was carried out in micro-plots. The different genotypes performed differently in grain yield. The genotypes WH-1063, WH-1054 and WH-1080 were relatively salt tolerant as they had higher mean grain yield as well as higher yield at EC of 7.5 dSm⁻¹. On the contrary, genotypes WH-1053 and WH-1076 were relatively salt sensitive on the basis of grain yield obtained. The photosynthetic CO₂ fixation rate decreased by about 19 and 30% when subjected to salt stress of 5.0 and 7.5 dSm⁻¹, respectively, however, reductions in stomatal conductance (gs) and transpiration rate were much greater, amounting to 42 and 63% for gs, and 34 and 50% for transpiration rate under the intermediate (5.0 dSm⁻¹) and high salt stress (7.5 dSm⁻¹), respectively. The reduction in inter cellular CO₂ concentration (Ci) was much lower, amounting to only 8 and 12%, respectively, at stress levels of 5.0 and 7.5 dSm⁻¹. Salt-tolerant cultivars (WH 1045, WH1054, WH1062, WH 1063, WH 1077, WH 1078 and WH 1080) had high stomatal conductance ranging from 0⋯185 to 0⋯382 mmol m^–2 s^–1. The intrinsic mesophyll efficiency showed a negative correlation with the yield (R² = 0⋯36), but a positive correlation of intrinsic carboxylation efficiency with yield (R² = 0⋯43) was observed. So it is assumed that intrinsic mesophyll and carboxylation efficiencies can be used as physiological parameters to screen wheat genotypes for salt tolerance.