Plant–microbe synergy: employing coastal plant bacteria for wheat prosperity under combined saline and heat stress

Abstract: Environmental stresses due to climate changes, such as high temperatures and land degradation, significantly impact crop yield, making innovative strategies necessary to increase plant stress tolerance. This study investigates the potential of plant growth-promoting rhizobacteria (PGPR) to enhance wheat resilience under multiple environmental stresses, such as high salinity and temperature. For this, 15 bacterial strains were isolated from the rhizosphere and roots of Pancratium maritimum and screened for their ability to withstand high salinity (50–600 mM NaCl) and elevated temperatures (up to 42 °C). The isolates were identified by 16S rRNA sequencing and tested for their PGP traits under combined abiotic stresses. Most of the strains exhibited PGP features, such as biofilm formation, phosphate solubilization, and phytohormone production. To enhance the growth of wheat plants, used as a model crop of commercial interest, three different consortia were designed and tested in vitro. The consortium (CONSIII), composed of Serratia marcescens ERA6, Enterobacter cloacae ERA9, and Bacillus proteolyticus ESOB2, provided synergistic effects that led to an enhancement in plant growth and stress resilience in vitro. This positive effect was confirmed in pot trials under double abiotic stress (37 °C, 132 mM NaCl), where CONSIII was able to boost the root and shoot growth, increase chlorophyll and carotenoid content, and enhance antioxidant activity, mitigating reactive oxygen species accumulation. These findings underscore the potential of PGPR consortia as bioinoculants for sustainable agriculture, demonstrating their effectiveness in the simultaneous presence of salinity and heat stresses—a challenging and under-investigated environmental scenario. Key points: • PGPR strains isolated from Pancratium maritimum rhizosphere are able to grow and exhibit PGP traits under combined salinity and heat conditions • The formulated consortium of PGPR strains (CONSIII) significantly enhances wheat growth and stress resilience under a multi-stress environment • CONSIII increases plant biomass, pigment content, and antioxidant activity, proving its value as a sustainable bioinoculant