The increasing heavy metal contamination in agricultural soils has become a serious concern across the globe. The present study envisages developing microbial inoculant approach for agriculture in Zn contaminated soils. Potential zinc tolerant bacteria (ZTB) were isolated from zinc (Zn) contaminated soils of southern Rajasthan, India. Isolates were further screened based on their efficiency towards Zn tolerance and plant growth promoting activities. Four strains viz. ZTB15, ZTB24, ZTB28 and ZTB29 exhibited high degree of tolerance to Zn up to 62.5 mM. The Zn accumulation by these bacterial strains was also evidenced by AAS and SEM–EDS studies. Assessment of various plant growth promotion traits viz., IAA, GA₃, NH₃, HCN, siderophores, ACC deaminase, phytase production and P, K, Si solubilization studies revealed that these ZTB strains may serve as an efficient plant growth promoter under in vitro conditions. Gluconic acid secreted by ZTB strains owing to mineral solubilization was therefore confirmed using high performance liquid chromatography. A pot experiment under Zn stress conditions was performed using maize (Zea mays) variety (FEM-2) as a test crop. Zn toxicity reduced various plant growth parameters; however, inoculation of ZTB strains alleviated the Zn toxicity and enhanced the plant growth parameters. The effects of Zn stress on antioxidant enzyme activities in maize under in vitro conditions were also investigated. An increase in superoxide dismutase, peroxidase, phenylalanine ammonia lyase, catalase and polyphenol oxidase activity was observed on inoculation of ZTB strains. Further, ZIP gene expression studies revealed high expression in the ZIP metal transporter genes which were declined in the ZTB treated maize plantlets. The findings from the present study revealed that ZTB could play an important role in bioremediation in Zn contaminated soils.

In the present study, 24 Azotobacter strains were isolated from soils of different areas of southern Rajasthan and characterized at biochemical, functional, and molecular levels. The isolated Azotobacter strains were gram negative and cyst forming when viewed under the microscope. These strains were also screened for their plant growth promoting activities and the ability of these isolates to survive under abiotic stress conditions viz. salt, pH, temperature, and drought stress. All the isolates showed IAA, siderophore, HCN, and ammonia production, whereas seven Azotobacter strains showed phosphate solubilization. Amplified Ribosomal DNA Restriction Analysis (ARDRA) revealed significant diversity among Azotobacter strains and the dendrogram obtained differentiated twenty‐four of the strains into two major clusters at a similarity coefficient of 0.64. Qualitative and quantitative N₂ fixation abilities of these strains were also detrained, and the amounts of acetylene reduced by Azotobacter strains were in the range of 1.31 to 846.56 nmol C₂H₄ mg protein⁻¹ h⁻¹. The strains showing high nitrogen fixation ability with multiple PGP activities were selected for further pot studies, and these Azotobacter strains significantly increased the various plant growth parameters of maize plantlets. Furthermore, the best Azotobacter isolates were subjected to 16S rRNA sequencing and confirmed their identities as Azotobacter sp. The indigenous Azotobacter strains with multiple PGP activities could be further used for commercial production.

Global agriculture is frequently subjected to stresses from increased salt content, drought, heavy metals, and other factors, which limit plant growth and production, deteriorate soil health, and constitute a severe danger to global food security. Development of environmentally acceptable mitigation techniques against stresses and restrictions on the use of chemical fertilizers in agricultural fields is essential. Therefore, eco‐friendly practises must be kept to prevent the detrimental impacts of stress on agricultural regions. The advanced metabolic machinery needed to handle this issue is not now existent in plants to deal against the stresses. Research has shown that the key role and mechanisms of arbuscular mycorrhiza fungi (AMF) to enhance plant nutrient uptake, immobilisation and translocation of heavy metals, and plant growth‐promoting attributes may be suitable agents for plant growth under diversed stressed condition. The successful symbiosis and the functional relationship between the plant and AMF may build the protective regulatory mechansm against the key challenge in particular stress. AMF’s compatibility with hyperaccumulator plants has also been supported by studies on gene regulation and theoretical arguments. In order to address this account, the present review included reducing the impacts of biotic and abiotic stress through AMF, the mechanisms of AMF to improve the host plant’s capacity to endure stress, and the strategies employed by AM fungus to support plant survival in stressful conditions.

Potassium (K) helps crop plants to resist biotic and abiotic challenges and plays a vital role in biochemical, metabolic, and physiological processes. Due to intense agricultural practices over the past few decades, the soil K reserve has been observed to be decreasing globally. It is possible to view potassium-solubilizing bacteria (KSB), which uses a number of biological mechanisms to convert potassium from inaccessible forms and make it accessible to crop plants, as a viable method for managing K in soils with low potassium levels. The present study encompasses 44 KSB strains isolated from rhizospheric soils collected from southern Rajasthan, India and characterized based on morphological, biochemical, and molecular profiles. All the isolates exhibited potassium solubilization and were identified using ERIC, BOX, REP PCR, and 16 S rDNA amplification which exhibited significant diversity amongst the strains. A flame-photometric analysis revealed that significant amounts of potassium were released by isolates from muscovite mica on the 21st day of incubation. These KSB strains produced hydrolytic enzymes and plant growth-promoting activities at different environmental stresses. In comparison to the absolute control (control without KSB), maize seedlings grown from bacterized seeds showed an increase in shoot length, root length, leaf number, total chlorophyll content, and the expression of stress-related enzymes. These native strains, which have a variety of advantageous traits, may be able to replace synthetic K fertilizers in order to increase food production while reducing pollution and restoring degraded land for agricultural use.