Mitigating the adverse effects of salt stress in pepper plants using two native strains: Cellulosimicrobium 60I1 and Pseudomonas 42P4

Soil salinity is one of the main abiotic factors causing plant stress and is a major cause of land degradation worldwide, especially in arid and semi-arid regions. High salinity in the root zone has a negative effect on most plant functions, limits biomass accumulation and significantly reduces crop productivity. The use of plant growth promoting rhizobacteria (PGPR) to enhance crop growth under saline conditions is an alternative to reduce chemical fertilization and the negative symptoms caused by salinity. The objective of this study was to evaluate the inoculation effect of Cellulosimicrobium 60I1 and Pseudomonas 42P4 on pepper plants grown under salinity stress. Pepper seedlings cv. Calafyuco INTA inoculated with both strains were grown under greenhouse conditions. Twenty-five days after inoculation, they were transplanted into plastic pots and treated with 100 mL of 150 mM NaCl or 100 mL of 200 mM Na₂SO₄ solutions, to induce the salt stress. A completely randomized design of nine treatments was established (three levels of the salt stress factor: without salt, NaCl and Na₂SO₄ per three levels of the bacteria factor: without PGPR, 60I1, 42P4). Seventy-five days after the sowing, morphological, physiological, and biochemical changes, including a profile of phenolic compounds, were evaluated. The results demonstrated that salt treatments, decreased the height (26–32 %), stem diameter (20–36 %), leaves per plant (22 %-non significant), root length (26–45 %), SPAD index (36–27 %), root and shoot dry weight (51–51 %), and survival percentage (20–100 %) of pepper plants grown in the greenhouse (with NaCl and Na₂SO_4, respectively). However, the inoculation with 42P4 increased root (76–58 %) and shoot dry weight (108–98 %); whereas 60I1 increased (60–35 %) and (95–92 %) with NaCl or Na₂SO_4, respectively, compared to the control without PGPR in plants grown under salinity stress conditions. Inoculated plants increased tolerance to salt conditions by reducing lipid peroxidation and increasing chlorophyll quantum efficiency, carotenoids, anthocyanins, and nitrogen levels. In addition, salt stress modified the phenolic compound profile and the inoculation maintained the levels of some compounds with antioxidant activity at levels similar to that of the unstressed control. This work highlights the importance of PGPR as an alternative to increase salt stress tolerance in crops in the context of climate change.