Field evaluation of the effects of salicylic acid and PGPR (Pseudomonas yamanorum) alone and in combination on growth, productivity, and PSII photochemistry in salt-stressed chili pepper

Chili pepper ( Capsicum annuum L.), particularly the Baklouti variety, is a glycophyte known for its limited growth and development under salinity conditions, which caused a high reduction in yield and physiochemical quality of the fruit. Salicylic acid (SA) and plant growth-promoting rhizobacteria (PGPR) are known to enhance plant tolerance to abiotic stress by modulating physiological processes. In this context, a field experiment was conducted to investigate the effect of 1 mM SA foliar spray and/or PGPR (Pseudomonas yamanorum ) root inoculation on pepper plants exposed to 50, 100, and 150 mM NaCl. Our findings demonstrated that salinity, especially 150 mM NaCl, markedly reduced vegetative growth, photosynthetic performance, chlorophyll fluorescence parameters, energy partitioning, and fruit yield and quality. Both SA and PGPR, applied individually or in combination, alleviated these salinity-induced effects. The combined treatment (SA-PGPR) was consistently the most effective across all stress levels, including extreme salinity (150 mM NaCl). It more than doubled plant dry weight, increased net photosynthesis by 30.3%, maximal efficiency of PSII by 35.7%, energy allocated to PSII photochemistry by 14.1% and yield by about twofold. In addition, the combined treatment reduced the excess of energy excitation by 15.5% and decreased fruit titratable acidity by 15.9%. These results highlight the strong potential of combining SA and PGPR to enhance pepper resilience under high salinity.