This review presents a comprehensive and systematic study of the field of bacterial plant biostimulants and considers the fundamental and innovative principles underlying this technology. Plant biostimulants are an important tool for modern agriculture as part of an integrated crop management (ICM) system, helping make agriculture more sustainable and resilient. Plant biostimulants contain substance(s) and/or microorganisms whose function when applied to plants or the rhizosphere is to stimulate natural processes to enhance plant nutrient uptake, nutrient use efficiency, tolerance to abiotic stress, biocontrol, and crop quality. The use of plant biostimulants has gained substantial and significant heed worldwide as an environmentally friendly alternative to sustainable agricultural production. At present, there is an increasing curiosity in industry and researchers about microbial biostimulants, especially bacterial plant biostimulants (BPBs), to improve crop growth and productivity. The BPBs that are based on PGPR (plant growth-promoting rhizobacteria) play plausible roles to promote/stimulate crop plant growth through several mechanisms that include (i) nutrient acquisition by nitrogen (N₂) fixation and solubilization of insoluble minerals (P, K, Zn), organic acids and siderophores; (ii) antimicrobial metabolites and various lytic enzymes; (iii) the action of growth regulators and stress-responsive/induced phytohormones; (iv) ameliorating abiotic stress such as drought, high soil salinity, extreme temperatures, oxidative stress, and heavy metals by using different modes of action; and (v) plant defense induction modes. Presented here is a brief review emphasizing the applicability of BPBs as an innovative exertion to fulfill the current food crisis.

Agriculture has a lot of responsibility as the rise in the world’s population demands more food requirements. However, more than one type of biotic and abiotic stress continually impacts agricultural productivity. Drought stress is a major abiotic stress that significantly affects agricultural productivity every year as the plants undergo several morphological, biochemical, and physiological modifications, such as repressed root and shoot growth, reduced photosynthesis and transpiration rate, excessive production of reactive oxygen species (ROS), osmotic adjustments, and modified leaf senescence regulating and stress signaling pathways. Such modifications may permanently damage the plants; therefore, mitigation strategies must be developed. The use of drought resistant crop cultivars is more expensive and labor-intensive with few advantages. However, exploiting plant growth promoting rhizobacteria (PGPR) is a proven alternative with numerous direct and indirect advantages. The PGPR confers induced systemic tolerance (IST) mechanisms in plants in response to drought stress via multiple mechanisms, including the alteration of root architecture, maintenance of high relative water content, improvement of photosynthesis rate, production of phytohormones, exopolysaccharides, ACC deaminase, carotenoids and volatiles, induction of antioxidant defense system, and alteration in stress-responsive gene expression. The commercial application of PGPR as bioinoculants or biostimulants will remain contingent on more robust strain selection and performance under unfavorable environmental conditions. This review highlights the possible mechanisms of PGPR by activating the plant adaptive defense systems for enhancing drought tolerance and improving overall growth and yield.

Drought stress is the major abiotic factor limiting crop production. Co-inoculating crops with nitrogen fixing bacteria and plant growth-promoting rhizobacteria (PGPR) improves plant growth and increases drought tolerance in arid or semiarid areas. Soybean is a major source of high-quality protein and oil for humans. It is susceptible to drought stress conditions. The co-inoculation of drought-stressed soybean with nodulating rhizobia and root-colonizing, PGPR improves the root and the shoot growth, formation of nodules, and nitrogen fixation capacity in soybean. The present study was aimed to observe if the co-inoculation of soybean (Glycine max L. (Merr.) nodulating with Bradyrhizobium japonicum USDA110 and PGPR Pseudomonas putida NUU8 can enhance drought tolerance, nodulation, plant growth, and nutrient uptake under drought conditions. The results of the study showed that co-inoculation with B. japonicum USDA110 and P. putida NUU8 gave more benefits in nodulation and growth of soybean compared to plants inoculated with B. japonicum USDA110 alone and uninoculated control. Under drought conditions, co-inoculation of B. japonicum USDA 110 and P. putida NUU8 significantly enhanced the root length by 56%, shoot length by 33%, root dry weight by 47%, shoot dry weight by 48%, and nodule number 17% compared to the control under drought-stressed. Co-inoculation with B. japonicum, USDA 110 and P. putida NUU8 significantly enhanced plant and soil nutrients and soil enzymes compared to control under normal and drought stress conditions. The synergistic use of B. japonicum USDA110 and P. putida NUU8 improves plant growth and nodulation of soybean under drought stress conditions. The results suggested that these strains could be used to formulate a consortium of biofertilizers for sustainable production of soybean under drought-stressed field conditions.

We have optimized a simple and rapid preparation procedure for mushroom DNA extraction from colonies on media or from fruiting bodies for PCR amplification. The protocol combines microwaving twice for 1 min, cooling for 10 min, and centrifuging for 5 min. By using this procedure, more than 100 samples of mushroom DNA can be prepared within 1 h. The DNA obtained can be used for (1) identifying mushroom species by PCR and subsequent sequencing, (2) amplifying low copy number genes (at least 2,000 bp), and (3) screening genetic transformants. This technique will contribute to the mycology of mushroom species.

Zinc (Zn) is an essential micronutrient required to enhance crop growth and yield. In the arid – semiarid region, Zn deficiency is expected due to alkaline calcareous soil. Contrarily, Zn toxicity is also becoming an environmental concern due to increasing anthropogenic activities (metal smelting, copper industry, etc.). Therefore, balanced Zn application is necessary to save resources and achieve optimum crop growth and yield. Most scientists suggest biological approaches to overcome the problem of Zn toxicity and deficiency. These biological approaches are mostly environment-friendly and cost-effective. In these biological approaches, the use of arbuscular mycorrhizae fungi (AMF) symbiosis is becoming popular. It can provide tolerance to the host plant against Zn-induced stress. Inoculation of AMF helps in balance uptake of Zn and enhances the growth and yield of crops. On the other hand, maize (Zea mays L.) is an important cereal crop due to its multifarious uses. As maize is an effective host for mycorrhizae symbiosis, that’s why this review was written to elaborate on the beneficial role of arbuscular mycorrhizal fungi (AMF). The review aimed to glance at the recent advances in the use of AMF to enhance nutrient uptake, especially Zn. It was also aimed to discuss the mechanism of AMF to overcome the toxic effect of Zn. We have also discussed the detailed mechanism and physiological improvement in the maize plant. In conclusion, AMF can play an imperative role in improving maize growth, yield, and balance uptake of Zn by alleviating Zn stress and mitigating its toxicity.

Among the biotic and abiotic stress affecting the physical, chemical, and biological properties of soil, salinity is a major threat that leads to the desertification of cultivable land throughout the world. The existence of diverse and versatile microbial populations inhabiting the nutrient-rich soil and varied soil conditions affects the soil dynamism. A normal soil constitutes 600 million bacteria belonging to about 20,000 species, which is reduced to 1 million with 5,000–8,000 species in stress conditions. Plant growth-promoting rhizobacteria (PGPR) are in symbiotic association with the plant system, which helps in combating the abiotic stress and increases the overall productivity and yield. These microorganisms are actively associated with varied cellular communication processes through quorum sensing and secondary metabolites such as the production of Indole-3-acetic acid (IAA), exopolysaccharide (EPS) siderophore, ammonia, ACC deaminase, and solubilization of phosphate. The present study focused on the isolation, identification, and characterization of the microorganisms isolated from the seacoast of Dandi, Navsari. Twelve isolates exhibited PGP traits at a high salt concentration of 15–20%. AD9 isolate identified as Bacillus halotolerans showed a higher ammonia production (88 ± 1.73 μg/mL) and phosphate solubilization (86 ± 3.06 μg/mL) at 15% salt concentration, while AD32^* (Bacillus sp. clone ADCNO) gave 42.67 ±1.20 μg/mL IAA production at 20% salt concentration. AD2 (Streptomyces sp. clone ADCNB) and AD26 (Achromobacter sp. clone ADCNI) showed ACC deaminase activity of 0.61 ± 0.12 and 0.60 ± 0.04 nM α-ketobutyrate/mg protein/h, respectively. AD32 (Bacillus sp. clone ADCNL) gave a high siderophore activity of 65.40 ± 1.65%. These isolates produced salinity ameliorating traits, total antioxidant activities, and antioxidant enzymes viz. superoxide dismutase (SOD), Glutathione oxidase (GSH), and catalase (CAT). Inoculation of the multipotent isolate that produced PGP traits and salinity ameliorating metabolites promoted the plant growth and development in rice under salinity stress conditions. These results in 50% more root length, 25.00% more plant dry weight, and 41% more tillers compared to its control.