Mineral-Solubilizing Bacteria-Mediated Enzymatic Regulation and Nutrient Acquisition Benefit Cotton's (Gossypium hirsutum L.) Vegetative and Reproductive Growth.

Many farmers' incomes in developing countries depend on the cultivation of major crops grown in arid and semi-arid regions. The agricultural productivity of arid and semi-arid areas primarily relies on chemical fertilizers. The effectiveness of chemical fertilizers needs to improve by integration with other sources of nutrients. Plant growth-promoting bacteria can solubilize nutrients, increase plant nutrient uptake, and supplement chemical fertilizers. A pot experiment evaluated the promising plant growth-promoting bacterial strain's effectiveness in promoting cotton growth, antioxidant enzymes, yield, and nutrient uptake. Two phosphate solubilizing bacterial strains (Bacillus subtilis IA6 and Paenibacillus polymyxa IA7) and two zinc solubilizing bacterial strains (Bacillus sp. IA7 and Bacillus aryabhattai IA20) were coated on cotton seeds in a single as well as co-inoculation treatments. These treatments were compared with uninoculated controls in the presence and absence of recommended chemical fertilizer doses. The results showed the co-inoculation combination of Paenibacillus polymyxa IA7 and Bacillus aryabhattai IA20 significantly increased the number of bolls, seed cotton yield, lint yield, and antioxidants activities, including superoxide dismutase, guaiacol peroxidase, catalase, and peroxidase. Co-inoculation combination of Bacillus subtilis IA6 and Bacillus sp. IA16 promoted growth attributes, including shoot length, root length, shoot fresh weight, and root fresh weight. This co-inoculation combination also increased soil nutrient content. At the same time, Paenibacillus polymyxa IA7 + Bacillus aryabhattai IA20 increased nutrient uptake by plant shoots and roots compared.

Combating iron and zinc malnutrition through mineral biofortification in maize through plant growth promoting Bacillus and Paenibacillus species.

Introduction: The burgeoning population of the world is causing food insecurity not only by less food availability but also by the malnutrition of essential nutrients and vitamins. Malnutrition is mostly linked with food having micronutrients lower than the optimal concentration of that specific food commodity and becoming an emerging challenge over the globe. Microbial biofortification in agriculture ensures nutritional security through microbial nitrogen fixation, and improved phosphate and zinc solubilization, which increase the uptake of these nutrients. The present study evaluates the novel plant growth-promoting rhizobacteria (PGPR) to biofortify maize gain. Methods: For this purpose, a pot and two field experiments for maize were conducted. PGPRs were applied alone and in combination for a better understanding of the biofortification potential of these strains. At physiological maturity, the growth parameters, and at harvest, the yield, microbial population, and nutritional status of maize were determined. Results and discussion: Results revealed that the consortium (ZM27+ZM63+S10) has caused the maximum increase in growth under pot studies like plant height (31%), shoot fresh weight (28%), shoot dry weight (27%), root fresh (33%) and dry weights (29%), and microbial count (21%) in the maize rhizosphere. The mineral analysis of the pot trial also revealed that consortium of ZM27+ZM63+S10 has caused 28, 16, 20, 11 and 11% increases in P, N, K, Fe, and Zn contents in maize, respectively, as compared to un-inoculated treatment in pot studies. A similar trend of results was also observed in both field trials as the consortium of ZM27+ZM63+S10 caused the maximum increase in not only growth and biological properties but also caused maximum biofortification of mineral nutrients in maize grains. The grain yield and 1000-grain weight were also found significantly higher 17 and 12%, respectively, under consortium application as compared to control. So, it can be concluded from these significant results obtained from the PGPR consortium application that microbial inoculants play a significant role in enhancing the growth, yield, and quality of the maize. However, the extensive evaluation of the consortium may help in the formulation of a biofertilizer for sustainable production and biofortification of maize to cope with nutritional security.

Appraising the potential of EPS-producing rhizobacteria with ACC-deaminase activity to improve growth and physiology of maize under drought stress.

Rhizobacteria containing 1-aminocyclopropane-1-carboxylic acid-deaminase (ACC-deaminase) and exopolysaccharides (EPS) activity are important to induce stress tolerance in plants. The present study was conducted to screen and characterize plant growth-promoting rhizobacteria (PGPR) with ACC-deaminase and EPS-producing activity for improving maize growth under drought stress. Eighty-five rhizobacterial strains were isolated from the rain-fed areas, among those 69 isolates were able to utilize ACC and 31 strains were found positive for EPS production. These strains containing ACC-deaminase and/or EPS-producing activity were subjected to drought tolerance assay by inducing water stress in media using polyethylene glycol 6000. Based on results of the drought tolerance bioassay, 12 most prominent strains were selected to evaluate their growth-promoting abilities in maize under water-stressed conditions by conducting jar trial. The impact of strains on maize growth parameters was variable. Strains with co-existence of ACC-deaminase and EPS-producing activity showed comparatively better results than those with either ACC-deaminase or EPS-producing activity only. These strains were also significantly better in improving the plant physiological parameters including photosynthesis rate, stomatal conductance, vapor pressure, water-use efficiency and transpiration rate. The strain D3 with co-existence of ACC-deaminase and EPS-producing activity was significantly better in colonizing maize roots, improving plant growth and physiological parameters. The strain was named as Bacillus velezensis strain D3 (accession number MT367633) as confirmed through results of 16S rRNA partial gene sequencing. It is concluded that the strains with co-existence of ACC-deaminase and EPS-producing activity could be better suited for improving crop growth and physiology under drought stress.

Exopolysaccharides and indole-3-acetic acid producing Bacillus safensis strain FN13 potential candidate for phytostabilization of heavy metals.

Microbial population of soils irrigated with industrial wastewater may contain certain exopolysaccharides (EPS) and indole-3-acetic acid (IAA) producing bacterial strains having the ability to tolerate heavy metals along with plant growth-promoting (PGP) traits. As cadmium is one of the most toxic heavy metals for soils, plants, animals, and human beings, the present study was planned to isolate and characterize EPS- and IAA-producing, Cd-tolerant bacterial strains having tolerance against heavy metals along with plant growth-promoting traits. A total of 30 rhizobacterial strains (FN1-FN30) were isolated from rhizosphere soil collected from fields around industrial areas and roadsides irrigated with industrial wastewater. Out of these, eight isolates with the combined ability of IAA production and EPS production were characterized for PGP traits. On the basis of multifarious PGP traits and the results of root colonization assay, three most efficient EPS- and IAA-producing, Cd-tolerant plant growth-promoting strains, i.e., FN13, FN14, and FN16, were selected for multiple metal (Cd, Pb, Ni, and Cu) tolerance test along with quantification of growth, and IAA and EPS production abilities under Cd stress. Increasing levels of Cd stress negatively affected the tested characteristics of these strains, but FN13 showed more stability in growth, IAA production (18.24 µg mL-1), and EPS production (148.99 µg mL-1) compared to other strains under Cd stress. The morphological and biochemical analysis confirmed FN13 as Gram-positive, rod-shaped bacteria with smooth colonies of yellow appearance. The strain FN13 has strong root colonization (3.36 × 106 CFU g-1) ability for mustard seedlings and can solubilize Zn and phosphate along with the production of HCN, ammonia, and siderophores. The 16S rRNA sequencing confirmed it as the Bacillus safensis strain FN13. It can be explored as potential phytostabilizing biofertilizer for heavy metal-contaminated soils.

Comparison of rhizosphere properties as affected by different Bt- and non-Bt-cotton (Gossypium hirsutum L.) genotypes and fertilization.

Incorporation of genetically modified crops in the cropping system raises the need for studying the effect of these crops on the soil ecosystem. The current study aimed to compare the effect of Bacillus thuringiensis (Bt)- and non-Bt-cotton (Gossypium hirsutum L.) genotypes on rhizosphere properties under fertilized and unfertilized soil conditions. One non-Bt-cotton (IUB 75) and four Bt-cotton varieties (IUB-222, MM-58, IUB-13, FH-142) were sown in a Randomized Complete Block Design (RCBD) in a factorial fashion with three replications under unfertilized (T1) and fertilized (T2 at NPK 310-170-110 kg ha-1) soil conditions. The culturable soil bacterial population was recorded at flowering, boll opening, and harvesting stages, while other rhizosphere biological and chemical properties were recorded at harvesting. Results revealed that Bt-cotton genotypes IUB-222 and FH-142 showed significantly higher rhizosphere total nitrogen, NH4+-N, available phosphorus, and available potassium. Total organic carbon and microbial biomass carbon was also maximum in the rhizosphere of IUB-222 under fertilized conditions. Similarly, bacterial population (CFU g-1) at flowering stage and at harvesting was significantly higher in the rhizosphere of IUB-222 as compared to non-Bt- (IUB-75) and other Bt-cotton genotypes under same growth conditions. It showed that Bt genotypes can help in maintaining soil macronutrients (total nitrogen, available phosphorus, and available potassium) under proper nutrient management. Moreover, Bt-cotton genotypes seem to strengthen certain biological properties of the soil, thus increasing the growth and yield capability, maintaining available nutrients in the soil as compared to non-Bt cotton, while no harmful effects of Bt cotton on soil properties was detected.

Effectiveness of halo-tolerant, auxin producing Pseudomonas and Rhizobium strains to improve osmotic stress tolerance in mung bean (Vigna radiata L.)

Halo-tolerant, auxin producing bacteria could be used to induce salt tolerance in plants. A number of Rhizobium and auxin producing rhizobacterial strains were assessed for their ability to tolerate salt stress by conducting osmoadaptation assay. The selected strains were further screened for their ability to induce osmotic stress tolerance in mung bean seedlings under salt-stressed axenic conditions in growth pouch/jar trials. Three most effective strains of Rhizobium and Pseudomonas containing ACC-deaminase were evaluated in combination, for their ability to induce osmotic stress tolerance in mung bean at original, 4, and 6 dS m-1 under axenic conditions. Results showed that sole inoculation of Rhizobium and Pseudomonas strains improved the total dry matter up to 1.4, and 1.9 fold, respectively, while the increase in salt tolerance index was improved up to 1.3 and 2.0 fold by the Rhizobium and Pseudomonas strains, respectively. However, up to 2.2 fold increase in total dry matter and salt tolerance index was observed due to combined inoculation of Rhizobium and Pseudomonas strains. So, combined application of Rhizobium and Pseudomonas strains could be explored as an effective strategy to induce osmotic stress tolerance in mung bean.

Efficacy of Rhizobium and Pseudomonas strains to improve physiology, ionic balance and quality of mung bean under salt-affected conditions on farmer's fields.

High ethylene concentration under different environmental stresses such as salinity is one of the contributing factors for premature senescence of different plant parts. Plants under salinity stress produce increased levels of ethylene which inhibit the plant growth and physiology thus deteriorating the quality of the produce. Some plant growth promoting rhizobacteria (PGPR) have the ability to improve quality of crops through reduction in detrimental effects of salinity on plant growth and physiology by lowering endogenous level of ethylene along with other mechanisms. Two field trials were conducted to evaluate the Rhizobium and Pseudomonas containing ACC-deaminase for their efficacy to reduce the effect of salinity on physiology, ionic and nutrient balance of mung bean. Results showed that salinity stress adversely affected the physiological parameters of mung bean. It decreased the CO(2) assimilation, stomatal conductance of water, relative water content, photosynthetic rate, transpiration rate and chlorophyll contents in mung bean but inoculation of either Rhizobium or Pseudomonas alone reduced adverse effect of salinity significantly. However, co-inoculation with Rhizobium and Pseudomonas was the most effective treatment and it diluted the adverse effects of salinity on relative water contents and CO(2) assimilation rate thus improving the photosynthetic rate, water use efficiency and chlorophyll content over the un-inoculated control. Co-inoculation improved the ionic balance and also increased the phosphorus and protein concentration in grain of mung bean. The results suggested that these strains could be effectively used to improve the growth, physiology and quality of mung bean under salt-affected conditions.

Effectiveness of halo-tolerant, auxin producing Pseudomonas and Rhizobium strains to improve osmotic stress tolerance in mung bean (Vigna radiata L.).

Halo-tolerant, auxin producing bacteria could be used to induce salt tolerance in plants. A number of Rhizobium and auxin producing rhizobacterial strains were assessed for their ability to tolerate salt stress by conducting osmoadaptation assay. The selected strains were further screened for their ability to induce osmotic stress tolerance in mung bean seedlings under salt-stressed axenic conditions in growth pouch/jar trials. Three most effective strains of Rhizobium and Pseudomonas containing ACC-deaminase were evaluated in combination, for their ability to induce osmotic stress tolerance in mung bean at original, 4, and 6 dS m(-1) under axenic conditions. Results showed that sole inoculation of Rhizobium and Pseudomonas strains improved the total dry matter up to 1.4, and 1.9 fold, respectively, while the increase in salt tolerance index was improved up to 1.3 and 2.0 fold by the Rhizobium and Pseudomonas strains, respectively. However, up to 2.2 fold increase in total dry matter and salt tolerance index was observed due to combined inoculation of Rhizobium and Pseudomonas strains. So, combined application of Rhizobium and Pseudomonas strains could be explored as an effective strategy to induce osmotic stress tolerance in mung bean.