In this study, the potential of co-application of biochar and seed priming with nano-sized chitosan-proline seed priming to improve salt tolerance in bread wheat was evaluated. For priming, the seeds of two differentially responding bread wheat genotypes, Messani White (salt-sensitive) and SIS-12 (salt-tolerant), were soaked in nano-sized chitosan-proline solution (nano-priming; 100 mM) or water (hydropriming) for 18 h. The wheat seeds were planted in plastic pots filled with acid-washed sand (2.5 kg) containing biochar (25 g kg(-1) sand) or not under normal (0 mM NaCl) or saline (120 mM NaCl) conditions. Salinity was imposed using NaCl in increments of 40 mM. Salinity stress significantly reduced the growth and carbon assimilation in both tested genotypes. Seed priming with nano-proline and the biochar application significantly improved plant growth and carbon assimilation. However, the combined use of biochar and nano-priming was more effective in improving salt tolerance in tested wheat genotypes than the sole application. Biochar application instead triggered sodium and chloride uptake but contributed to salt tolerance through an increase in potassium contents, accumulation of proline, and activation of the antioxidant defense system. Nano-priming improved the salt tolerance in tested wheat genotypes through ionic homeostasis, activation of the antioxidant defense system, and osmotic adjustment. Co-application of biochar and nano-priming significantly improved salt tolerance in wheat genotypes through ionic homeostasis, osmotic adjustment, maintenance of tissue water status, activation of antioxidant defense system, continuation of the carbon assimilation, and sustained plant growth.
