Recent changes in climate have reduced crop productivity throughout much of the world. Drought and heat stress, particularly in arid and semi‐arid regions, have seriously affected barley production. This study explored the separate and interactive effects of silicon (Si) and hydrogen sulphide (H2S) on plant growth and mitigation of the adverse effects of heat stress (DS) and drought stress (HS) in a barley pot experiment. The impacts of simultaneous DS + HS were more severe than individual stresses due to increased ROS production, malondialdehyde (MDA) content and higher electrolyte leakage (EL), thereby leading to reduced water, protein and photosynthetic pigment content. Exogenously applied Si and H2S alleviated the DS‐, HS‐ and DS + HS‐induced effects on barley by reducing ROS production, MDA and EL. A single application of H2S or Si + H2S increased plant biomass under all stress conditions, which can be ascribed to higher Si accumulation in barley shoots. A single application of Si or H2S significantly increased plant biomass. However, Si + H2S was the most effective treatment for metabolite accumulation and elevating activity of antioxidant enzymes to prevent toxicity from oxidative stress. This treatment also modulated osmolyte content, enhanced antioxidant activity and regulated the stress signalling‐related endogenous hormones, abscisic acid (ABA) and indole acetic acid (IAA). Exogenous treatments regulated endogenous H2S and Si and resulted in higher tolerance to individual and combined drought and heat stress in barley.

Microorganisms can interact with plants to promote plant growth and act as biocontrol agents. Associations with plant growth-promoting rhizobacteria (PGPR) enhance agricultural productivity by improving plant nutrition and enhancing protection from pathogens. Microbial applications can be an ideal substitute for pesticides or fungicides, which can pollute the environment and reduce biological diversity. In this study, we isolated 68 bacterial strains from the root-adhering soil of quinoa (Chenopodium quinoa) seedlings. Bacterial strains exhibited several PGPR activities in vitro, including nutrient solubilization, production of lytic enzymes (cellulase, pectinase and amylase) and siderophore synthesis. These bacteria were further found to suppress the mycelial growth of the fungal pathogen Alternaria alternata. Nine bacterial strains were selected with substantial antagonistic activity and plant growth-promotion potential. These strains were identified based on their 16S rRNA gene sequences and selected for in planta experiments with tomato (Solanum lycopersicum) to estimate their growth-promotion and disease-suppression activity. Among the selected strains, B. licheniformis and B. pumilus most effectively promoted tomato plant growth, decreased disease severity caused by A. alternata infection by enhancing the activities of antioxidant defense enzymes and contributed to induced systemic resistance. This investigation provides evidence for the effectiveness and viability of PGPR application, particularly of B. licheniformis and B. pumilus in tomato, to promote plant growth and induce systemic resistance, making these bacteria promising candidates for biofertilizers and biocontrol agents.

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