Integrating multitrait physiological approaches to characterize salinity tolerance in bread wheat (Triticum aestivum L.) genotypes

Soil salinity is a major constraint to wheat production because it disrupts plant water relations, photosynthesis, oxidative balance and yield formation. Although numerous physiological traits have been investigated individually, integrative approaches for evaluating coordinated physiological responses to salinity remain limited. This study investigated whether multitrait physiological integration could contribute to the characterization of salinity tolerance in the evaluated wheat genotypes using conventional physiological analyses together with cost–benefit slope analysis and the integrated physiological efficiency index (IPE ridge ). Three contrasting bread wheat genotypes [BAW 1147 (tolerant), BARI Gom 25 (moderately tolerant) and BARI Gom 28 (susceptible)] were evaluated under control, 5 and 10 dS m -1 electrical conductivity (EC) of the irrigation solution in a split-plot experiment arranged in a randomized complete block design. Water relations, gas exchange, photosynthetic pigments, compatible solute accumulation, oxidative stress, antioxidant defence and yield-related traits were assessed and physiological coordination was further evaluated using cost–benefit slope analysis and the integrated physiological efficiency index (IPE ridge ). Salinity (EC) of the irrigation solution reduced plant water status, photosynthetic performance, pigment stability and yield while increasing compatible solute accumulation, oxidative stress indicators and antioxidant enzyme activities. Among the evaluated genotypes, BAW 1147 generally maintained higher relative water content, photosynthetic rate, water use efficiency, chlorophyll content and grain yield, together with lower oxidative damage, than BARI Gom 25 and BARI Gom 28. Correlation analysis suggested stronger coordination among physiological and yield-related traits under saline irrigation conditions than under control conditions. Cost–benefit slope analysis revealed genotype- and irrigation solution EC-dependent differences in the relative contributions of the physiological response modules, whereas IPE ridge values were generally higher in the tolerant genotype than in the moderately tolerant and susceptible genotypes. The findings suggest that salinity tolerance in the evaluated wheat genotypes was associated with coordinated physiological responses rather than the performance of individual traits alone. The proposed cost–benefit slope analysis and IPE ridge index may provide complementary quantitative approaches for characterizing multitrait physiological responses within the present dataset. However, further validation across larger and more diverse wheat populations and environmental conditions is required before their broader applicability can be established.