Plant extracts and plant growth promoting rhizobacteria: seed bio-priming approach to improve tolerance of Lactuca sativa L. under salt stress

Seed bio-priming via biostimulants is an ecofriendly and smart approach that offers beneficial advantages in managing environmental constraints and thus deserves a particular attention. The aim of this study is to investigate the role of seed bio-priming via plant extracts and plant-growth-promoting rhizobacteria (PGPR) on germination rate, plant growth, mineral status, biomarkers of stress, phenolic compounds, and enzymatic activities in Lactuca sativa when subjected to salinity (150 mM NaCl). Our results demonstrate a potent effect attributed to all various agents in improving L. sativa response under salinity condition. In fact, all agents improved the germination rate, mainly with Globularia alypum (G) and Bacillus subtilis (BS) at 150 mM NaCl. In addition, the same tendency was observed on fresh weight, in which BS and G demonstrate a promising effect when compared with other agents. This result was again evinced in mineral nutrition when priming effectively enhanced bioactive molecules such as polyphenol, flavonoid, and tannin contents under stress conditions. That response was also correlated with antioxidant capacity response. The priming agents mitigated the oxidative stress and induced stimulation of enzymatic activity, including peroxidases (POD), polyphenol oxidase (PPO), and phenylalanine ammonialyase (PAL), particularly with bacteria and Globularia alypum. The application of bacteria and plant extracts in agriculture has proved to be an essential key to improve stress resilience. Thus, it is essential to decipher the mechanisms of bio-priming to effectively use this technique toward agricultural sustainability.