Plant Growth-Promoting Rhizobacteria Improve Growth, Morph-Physiological Responses, Water Productivity, and Yield of Rice Plants Under Full and Deficit Drip Irrigation

Enhancing sweet potato (Ipomoea batatas) resilience grown in cadmium-contaminated saline soil: a synergistic approach using Moringa leaf extract and effective microorganisms application

Raising soil contamination with cadmium (Cd2+) and salinization necessitates the development of green approaches using bio-elicitors to ensure sustainable crop production and mitigate the detrimental health impacts. Two field trials were carried out to study the individual and combined effects of foliage spraying of Moringa leaf extract (MLE) and soil application of effective microorganisms (EMs) on the physio-biochemical, osmolytes, antioxidants, and performance of sweet potato grown in Cd2+-contaminated salty soil (Cd2+  = 17.42 mg kg-1 soil and soil salinity ECe = 7.42 dS m-1). Application of MLE, EMs, or MLE plus EMs significantly reduced the accumulation of Cd2+ in roots by 55.6%, 50.0%, or 68.1% and in leaves by 31.4%, 27.6%, or 38.0%, respectively, compared to the control. Co-application of MLE and EMs reduced Na+ concentration while substantially raising N, P, K+, and Ca2+ acquisition in the leaves. MLE and EMs-treated plants exhibited higher concentrations of total soluble sugar by 69.6%, free proline by 47.7%, total free amino acids by 29.0%, and protein by 125.7% compared to the control. The enzymatic (SOD, APX, GR, and CAT) and non-enzymatic (phenolic acids, GSH, and AsA) antioxidants increased in plants treated with MLE and/or EMs application. Applying MLE and/or EMs increased the leaf photosynthetic pigment contents, membrane stability, relative water content, water productivity, growth traits, and tuber yield of Cd2+ and salt-stressed sweet potato. Consequently, the integrative application of MLE and EMs achieved the best results exceeding the single treatments recommended in future application to sweet potato in saline soil contaminated with Cd2+.

Coinoculation with Growth-Promoting Bacteria Increases the Efficiency of Nitrogen Use by Irrigated Rice

Considering the importance of rice (Oryza sativa L.) for global food and its significant production in Brazil, strategies for its sustainable production are focused on technologies to increase productivity and decrease the use of chemical nitrogen fertilizers. An alternative for this is the use of plant growth-promoting bacteria that have proven to be efficient for increasing production and nutrient promotion in cereals. This study reports the use of coinoculation with Azospirillum brasilense and Pseudomonas fluorescens to inoculate irrigated rice through seed treatment (ST) with inoculant and seed inoculation in planting furrow technology (PFT) in four field experiments. The inoculation technologies increased rice yields in the presence of A. brasilense + P. fluorescens and with a reduction in mineral N (30 kg of N ha-1), equal to or greater when nitrogen fertilizer was present alone. Our results demonstrate that coinoculation with A. brasilense (strain Ab-V6) and P. fluorescens (strain CCTB03) increases the efficiency of N use from a mineral source in irrigated rice, with an increase of 37% in economic production (grains per unit of N applied), providing better agronomic performance of the crop.

Application of bio-organic amendments improves soil quality and yield of fennel (Foeniculum vulgare Mill.) plants in saline calcareous soil

The impact of bio-organic amendments on crop production is poorly understood in saline calcareous soils. The aim in the present study was to determine the effects of the application of organic manure along with lactic acid bacteria (LAB) on soil quality, and morpho-physio-biochemical responses, seed yield (SY) and essential oil yield (EOY) of fennel plants (Foeniculum vulgare Mill.) grown in saline calcareous soils. Eight treatments of farmyard manure (FM) or poultry manure (PM) individually or combined with Lactobacillus plantarum (Lp) and/or Lactococcus lactis (Ll) were applied to saline calcareous soil in two growing seasons. Either FM or PM combined with LAB had beneficial effects on lowering ECe, pH and bulk density and increasing total porosity, organic matter, and water and nutrient retention capacities in addition to total bacterial population in the soil. Growth, nutrient uptake, SY and EOY of plants were also enhanced when fennel seeds were inoculated with Lp and/or Ll and the soil was amended with any of the organic manures under unfavorable conditions. Compared to control (no bio-organic amendments), FM + Lp + Lt or PM + Lp + Lt treatment signficantlly (P ≤ 0.05) increased plant height by 86.2 or 65.0%, total chlorophyll by 73 or 50%, proline by 35 or 45%, glutathione by 100 or 138%, SY by 625 or 463% and EOY by 300 or 335%, respectively, in fennel plants. Co-application of the naturally occurring microorganisms (i.e., LAB) and organically-derived, nutrient-rich fertilizer (i.e., FM or PM) is recommended to improve yield of fennel plants in saline calcareous soils.

Effects of fresh and field-aged holm-oak biochar on As, Cd and Pb bioaccumulation in different rice growing environments

Arsenic, Cd, and Pb environmental fate is influenced when the traditional permanent flooding rice production systems are replaced by water-saving and soil conservation practices, urging for additional strategies that avoid their bioaccumulation in rice grain. The aim of this two-years field study was to evaluate the effects of fresh and field-aged biochar on As, Cd, and Pb bioaccumulation, and on As speciation, in rice grain produced in different growing environments (flooding versus sprinkler and conventional tillage versus direct seeding). Biochar produced from holm-oak pruning residues (pyrolysis at 550 °C, 48 h), in a single application (28 Mg ha^-1), reduced As bioaccumulation in rice grain in the permanent flooding system to non-quantifiable concentrations (e.g., from 0.178 mg kg^-1 to <0.04 mg kg^-1, for inorganic-As, respectively), an effect which remained under field-aging conditions, increasing rice commercial value. When adopting sprinkler irrigation, the undesirable increase in Cd bioaccumulation in rice, relatively to the anaerobic system, was counteracted by biochar application, reducing its bioaccumulation in kernels between 32 and 80 %, allowing a simultaneous control of metals and metalloids bioaccumulation in rice. The bioaccumulation of Pb was also prevented with biochar application, with a reduction in its concentration four- to 13-times, in all the management systems, relatively to the non-amended plots, under fresh biochar effects. However, Pb immobilization decreased with biochar field-aging, indicating that the biochar application may have to be repeated to maintain the same beneficial effect. Therefore, the present study shows that the implementation of sprinkler irrigation with holm-oak biochar could reduce the risk of heavy metals(loids) bioaccumulation in rice grains and, thereby, ensuring food safety aspects, particularly under fresh biochar effects.

Mitigation of water scarcity with sustained growth of Rice by plant growth promoting bacteria

Climate change augments the risk to food security by inducing drought stress and a drastic decline in global rice production. Plant growth-promoting bacteria (PGPB) have been known to improve plant growth under drought stress. Here in the present study, we isolated, identified, and well-characterized eight drought-tolerant bacteria from the rice rhizosphere that are tolerant to 20% PEG-8000. These strains exhibited multiple plant growth-promoting traits, i.e., 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity, exopolysaccharide production, phosphate (P)-solubilizing activity (51-356 µg ml-1), indole-3 acetic acid (IAA) production (14.3-46.2 µg ml-1), and production of organic acids (72-178 µg ml-1). Inoculation of bacterial consortium (Bacillus subtilis NM-2, Brucella haematophilum NM-4, and Bacillus cereus NM-6) significantly improved seedling growth and vigor index (1009.2-1100) as compared to non-inoculated stressed plants (630-957). Through rhizoscanning, efficiency of the consortium was validated by improved root parameters such as root length (17%), diameter, and surface area (18%) of all tested genotypes as compared with respective non-inoculated stressed treatments. Furthermore, the response of consortium inoculation on three rice genotypes was positively correlated with improved plant growth and drought stress ameliorating traits by the accumulation of osmoprotectant, i.e., proline (85.8%-122%), relative water content (51%), membrane stability index (64%), and production of antioxidant enzymes to reduce oxidative damage by reactive oxygen species. A decrease in temperature and improved chlorophyll content of inoculated plants were found using infrared thermal imaging and soil plant analyzer development (SPAD), respectively. The key supporting role of inoculation toward stress responses was validated using robust techniques like infrared thermal imaging and an infrared gas analyzer. Furthermore, principal component analysis depicts the contribution of inoculation on stress responses and yield of tested rice genotypes under water stress. The integration of drought-tolerant rice genotype (NIBGE-DT02) and potential bacterial strains, i.e., NM-2, NM-4, and NM-6, can serve as an effective bioinoculant to cope with water scarcity under current alarming issues related to food security in fluctuating climate.

Bioformulations Derived from Enterobacter sp. NRRU-N13 and Oligochitosan Alleviate Drought Stress in Thai Jasmine Rice (Oryza sativa L. var. KDML105)

Climate change is predicted to increase the length, severity, and frequency of drought, which limits plant development by changing various physiological and biochemical processes. Therefore, the present study investigated the effects of drought stress on indole-3-acetic and exopolysaccharide production by Enterobacter sp. NRRU-N13, developed bioformulations of plant growth-promoting Enterobacter sp. NRRU-N13, and evaluated the synergistic effects of these bioformulations in combination with different chitosans on the physiological responses of rice under drought stress. Drought stress inhibited the biosynthesis of indole-3-acetic and exopolysaccharides by Enterobacter sp. NRRU-N13. The viability and stability of Enterobacter sp. NRRU-N13 in bioformulations ranged between 4.70 and 5.70 log CFU g-1 after 80 days at an ambient temperature. Oligochitosan and chitosan at 40‍ ‍mg L-1 were appropriate concentrations for improving rice seedling growth, namely, plant height, root length, shoot and root fresh weights, biomass, and the vigor index (P<0.05). The abilities of these bioformulations, in combination with oligochitosan and chitosan, to alleviate drought stress in rice were examined. The results obtained revealed that the combined application of oligochitosan (40‍ ‍mg L-1) and the FON13 bioformulation (filter cake+40‍ ‍mg kg-1 oligochitosan+10% Enterobacter sp. NRRU-N13) exerted the strongest synergistic effects to alleviate drought stress in rice plants by increasing ascorbate peroxidase and catalase activities, chlo-rophyll concentrations, and relative water content and suppressing proline accumulation and electrolyte leakage from rice plants under drought stress. The present results indicate that the application of oligochitosan combined with these bioformulations effectively improved plant physiology and development. Therefore, the combined application of oligochitosan and a bioformulation of Enterobacter sp. NRRU-N13 is recommended to alleviate drought stress in rice plants.

Synergistic impact of nanomaterials and plant probiotics in agriculture: A tale of two-way strategy for long-term sustainability

Modern agriculture is primarily focused on the massive production of cereals and other food-based crops in a sustainable manner in order to fulfill the food demands of an ever-increasing global population. However, intensive agricultural practices, rampant use of agrochemicals, and other environmental factors result in soil fertility degradation, environmental pollution, disruption of soil biodiversity, pest resistance, and a decline in crop yields. Thus, experts are shifting their focus to other eco-friendly and safer methods of fertilization in order to ensure agricultural sustainability. Indeed, the importance of plant growth-promoting microorganisms, also determined as "plant probiotics (PPs)," has gained widespread recognition, and their usage as biofertilizers is being actively promoted as a means of mitigating the harmful effects of agrochemicals. As bio-elicitors, PPs promote plant growth and colonize soil or plant tissues when administered in soil, seeds, or plant surface and are used as an alternative means to avoid heavy use of agrochemicals. In the past few years, the use of nanotechnology has also brought a revolution in agriculture due to the application of various nanomaterials (NMs) or nano-based fertilizers to increase crop productivity. Given the beneficial properties of PPs and NMs, these two can be used in tandem to maximize benefits. However, the use of combinations of NMs and PPs, or their synergistic use, is in its infancy but has exhibited better crop-modulating effects in terms of improvement in crop productivity, mitigation of environmental stress (drought, salinity, etc.), restoration of soil fertility, and strengthening of the bioeconomy. In addition, a proper assessment of nanomaterials is necessary before their application, and a safer dose of NMs should be applicable without showing any toxic impact on the environment and soil microbial communities. The combo of NMs and PPs can also be encapsulated within a suitable carrier, and this method aids in the controlled and targeted delivery of entrapped components and also increases the shelf life of PPs. However, this review highlights the functional annotation of the combined impact of NMs and PPs on sustainable agricultural production in an eco-friendly manner.

Piper caninum extract and Brevibacillus agri mixture suppresses rice leaf spot pathogen; Nigrospora oryzae and improves the production of red rice (Oryza sativa L)

Under the guise of enhancing productivity, using pesticides and artificial fertilizers in agriculture affects both the environment and living things. High chemical residues in food and the environment disrupt the health of consumers. One of the solutions that can bring about a reduction in the use of pesticides and chemicals is switching to organic fertilizers. The application of biopesticides originating from biological sources such as plant extracts and the use of microbes is gaining global acceptance. Therefore, this study aimed to obtain the best biopesticides and biostimulants that could suppress the leaf spot pathogen, Nigrospora oryzae, and increase the growth and yield of Bali red rice. The study contained four treatments, namely untreated control (F0), Piper caninum leaf extract (F1), Brevibacillus agri (F2), and fermented P. caninum leaf extract plus B. agri (F3). The treatments were arranged in a randomized complete block design, and each treatment was replicated three times. The parameters measured were the number of tillers per plant, number of leafs per plant, chlorophyll content, number of grains per panicle, grain weight, and grain yield. Furthermore, antimicrobial and antioxidants were assayed using SEM. GC-MS. At the end of the experiment, the disease index of the leaf spot was measured. The results showed that F3 significantly suppressed leaf spots caused by N. oryzae compared to other treatments, including untreated control in red rice. Additionally, the F3 significantly increased the number of productive tillers, number of grains per panicle, and grain yield compared to all other treatments. The F3 enhanced the crop yield at 6.19 tons/ha, an increase of 50% compared to the untreated control. The SEM.GC-MS results showed the presence of 2.3 butanediol, tetra-decanoic acid, butanoic acid, ethyl ester, benzene propanal, 3-(1,1-dimethylethyl)-a-methyl, a-N-Normethadol in treated plants with P. canicum plus B. agri.

Isolation and Characterization of Novel Biological Control Agent Clostridium beijerinckii against Meloidogyne incognita

One of the most severe soil-borne pathogens in the world is the root-knot nematode (Meloidogyne incognita). Biological control is gaining more importance as environmental awareness increases. Thus, keeping this in mind, a total of 712 bacterial strains were isolated from 117 rhizosphere soil samples and investigated for potential biological control activity against M. incognita. Strain Sneb518 (Clostridium beijerinckii) was identified as having solid biocontrol activity against M. incognita. Sneb518 demonstrated significant inhibition against M. incognita, with J2 mortality reaching 90.73% at 12 h and with eggs hatching at a rate of 6.00% at 24 h, compared to a hatchability level of 29.07% for the control. Additionally, Sneb518 was excellent for enhancing seed germination. The seeds coated with a fermentation broth containing Sneb518 efficiently boosted the germination rate to 88.49%. The effectiveness and stability of C. beijerinckii Sneb518 against M. incognita were then further evaluated in a greenhouse. According to the pot experiment data, Sneb518 considerably (p < 0.05) reduced the number of root galls and egg masses on roots and also significantly (p < 0.05) increased tomato plant growth. C. beijerinckii Sneb518-treated tomato seedlings exhibited 50.26% biocontrol effectiveness compared to the control group. Our results demonstrate that C. beijerinckii Sneb518 can be a potential biological control agent against root-knot nematode disease and a biomass enhancer. This research will give new options for the sustainable control of root-knot nematode disease in tomatoes and other host plants.

Pseudomonas and Curtobacterium Strains from Olive Rhizosphere Characterized and Evaluated for Plant Growth Promoting Traits

Plant growth promoting (PGP) bacteria are known to enhance plant growth and protect them from environmental stresses through different pathways. The rhizosphere of perennial plants, including olive, may represent a relevant reservoir of PGP bacteria. Here, seven bacterial strains isolated from olive rhizosphere have been characterized taxonomically by 16S sequencing and biochemically, to evaluate their PGP potential. Most strains were identified as Pseudomonas or Bacillus spp., while the most promising ones belonged to genera Pseudomonas and Curtobacterium. Those strains have been tested for their capacity to grow under osmotic or salinity stress and to improve the germination and early development of Triticum durum subjected or not to those stresses. The selected strains had the ability to grow under severe stress, and a positive effect has been observed in non-stressed seedlings inoculated with one of the Pseudomonas strains, which showed promising characteristics that should be further evaluated. The biochemical and taxonomical characterization of bacterial strains isolated from different niches and the evaluation of their interaction with plants under varying conditions will help to increase our knowledge on PGP microorganisms and their use in agriculture.

Plant Growth-Promoting Rhizobacteria Improve Growth and Fruit Quality of Cucumber under Greenhouse Conditions

Cucumber fruit is rich in fiber, carbohydrates, protein, magnesium, iron, vitamin B, vitamin C, flavonoids, phenolic compounds, and antioxidants. Agrochemical-based production of cucumber has tripled yields; however, excessive synthetic fertilization has caused problems in the accumulation of salts in the soil and has increased production costs. The objective of this study was to evaluate the effect of three strains of plant growth-promoting rhizobacteria (PGPR) on cucumber fruit growth and quality under greenhouse conditions. The rhizobacteria Pseudomonas paralactis (KBendo6p7), Sinorhizobium meliloti (KBecto9p6), and Acinetobacter radioresistens (KBendo3p1) was adjusted to 1 × 10⁸ CFU mL⁻¹. The results indicated that the inoculation with PGPR improved plant height, stem diameter, root length, secondary roots, biomass, fruit size, fruit diameter, and yield, as well as nutraceutical quality and antioxidant capacity, significantly increasing the response of plants inoculated with A.radioresistens and S.meliloti in comparison to the control. In sum, our findings showed the potential functions of the use of beneficial bacteria such as PGPR for crop production to reduce costs, decrease pollution, and achieve world food safety and security.