Bacillus aryabhattai SRB02 tolerates oxidative and nitrosative stress and promotes the growth of soybean by modulating the production of phytohormones

Exiguobacterium aurantiacum SA100 induces antioxidant enzymes and salinity tolerance gene expression in wheat

This study evaluated the effects of Exiguobacterium aurantiacum SA100 on wheat (Triticum aestivum) growth under varying levels of salinity stress. Results indicated that SA100 significantly enhanced seed germination, root and shoot length, and fresh and dry biomass across salinity levels, particularly at 50 and 100 mM NaCl. Inoculation improved antioxidant enzyme activities (CAT, APX, POD, PPO), increased total phenolic content, and reduced oxidative damage by lowering MDA and H2O2 levels under 150 mM salinity. Ionic balance was maintained, with significant increases in K+, Mg++, and Ca++ and a reduction in Na+ accumulation. Gene expression analysis revealed upregulation of salt-tolerance genes (NAC7, NHX1, SOS1) and downregulation of stress-responsive genes (GS1, DREB2, DHN13, WRKY32). Principal component analysis confirmed that SA100 promotes salinity tolerance by modulating both biochemical and molecular responses. These findings suggest E. aurantiacum SA100 as a promising bioinoculant for enhancing wheat resilience under salinity stress.

Bacillus megaterium NCT-2 agent alters soil nutrients, vegetable quality, and root microecology in secondary salinized soil

Microbial remediation technology has the characteristics of high efficiency and environmental protection, which has attracted attention. However, there is complexity in the microorganism-soil-plant system. The effects of microbial agents on soil nutrients, plant quality, rhizosphere, and endophytic microorganisms are still unclear. Here, we demonstrate the application of Bacillus megaterium NCT-2 as a multifunctional agent that concurrently addresses salinization-driven nutrient imbalances and reshapes keystone microbial taxa to restore soil-plant homeostasis. The results showed that NCT-2 agent improved the soil nutrients, reduced the loss of nitrogen and sulfur, increased the content of available phosphorus, and decreased the electrical conductivity. The agent increased the number of bacteria and fungi in the soil. Meanwhile, NCT-2 agent improved the vegetable quality and yield. Specifically, the NCT-2 agent significantly increased the aboveground fresh weight, underground fresh weight, total flavonoids, antioxidant enzyme activity, ascorbic acid, Cu, Zn, Fe, P, and K in lettuce, while significantly reduced nitrate. The chlorophyll a, chlorophyll b, carotenoids, and total chlorophyll were significantly increased by the agent. Critically, high-throughput sequencing revealed NCT-2-driven enrichment of stress-resilient taxa (e.g., Firmicutes, Acidobacteria) and functional synergists (e.g., Acetobacter), which correlated with soil nutrient fluxes and plant antioxidant capacity. By decoupling the interplay between microbial community restructuring and systemic remediation outcomes, this work establishes a novel framework for leveraging keystone taxa to optimize salinized agroecosystems.

Unravelling the secrets of soil microbiome and climate change for sustainable agroecosystems

The soil microbiota exhibits an important function in the ecosystem, and its response to climate change is of paramount importance for sustainable agroecosystems. The macronutrients, micronutrients, and additional constituents vital for the growth of plants are cycled biogeochemically under the regulation of the soil microbiome. Identifying and forecasting the effect of climate change on soil microbiomes and ecosystem services is the need of the hour to address one of the biggest global challenges of the present time. The impact of climate change on the structure and function of the soil microbiota is a major concern, explained by one or more sustainability factors around resilience, reluctance, and rework. However, the past research has revealed that microbial interventions have the potential to regenerate soils and improve crop resilience to climate change factors. The methods used therein include using soil microbes' innate capacity for carbon sequestration, rhizomediation, bio-fertilization, enzyme-mediated breakdown, phyto-stimulation, biocontrol of plant pathogens, antibiosis, inducing the antioxidative defense pathways, induced systemic resistance response (ISR), and releasing volatile organic compounds (VOCs) in the host plant. Microbial phytohormones have a major role in altering root shape in response to exposure to drought, salt, severe temperatures, and heavy metal toxicity and also have an impact on the metabolism of endogenous growth regulators in plant tissue. However, shelf life due to the short lifespan and storage time of microbial formulations is still a major challenge, and efforts should be made to evaluate their effectiveness in crop growth based on climate change. This review focuses on the influence of climate change on soil physico-chemical status, climate change adaptation by the soil microbiome, and its future implications.

Improving Soybean Development and Grain Yield by Complementary Inoculation with Growth-Promoting Bacteria Azospirillum, Pseudomonas, Priestia, and Bacillus

Bioinputs are natural products applied to crops that contribute to more sustainable agriculture by boosting yields and reducing environmental impacts. In Brazil, the use of bioinputs such as Bradyrhizobium in soybean has been consolidated, but the expansion of on-farm bioinput production is currently initiating a new revolution. Furthermore, applications of bioinputs to cash crops in Brazil have shed light on the great potential of such growth-promoting microorganisms (GMPs) to improve nutrient uptake and increase productivity. This study explores the effect of the complementary inoculation with growth-promoting bacteria of post-emergence soybean, previously inoculated with Bradyrhizobium spp. Five treatments with growth-promoting bacteria were evaluated: T1-Control (no inoculation); T2-Azospirillum brasilense; T3-Pseudomonas fluorescens and Azospirillum brasilense; T4-Priestia aryabhattai, Bacillus haynesii, and Bacillus circulans; and T5-Priestia megaterium and Bacillus subtilis. In comparison with the control, all treatments with growth-promoting bacteria of the genera Azospirillum, Pseudomonas, Priestia, and Bacillus, applied after soybean emergence, induced 4-7% higher grain yields. Co-inoculation with Priestia megaterium and Bacillus subtilis (treatment T5) resulted in a higher 1000-grain weight, while Priestia aryabhattai, Bacillus haynesii, and Bacillus circulans (treatment T4) increased the number of pods and shoot dry weight. Our conclusion is that bioinputs increase soybean productivity and make agriculture more sustainable and efficient.

The synergistic interaction effect between biochar and plant growth-promoting rhizobacteria on beneficial microbial communities in soil

Excessive use of chemical fertilizers and extensive farming can degrade soil properties so that leading to decline in crop yields. Combining plant growth-promoting rhizobacteria (PGPR) with biochar (BC) may be an alternative way to mitigate this situation. However, the proportion of PGPR and BC at which crop yield can be improved, as well as the improvement effect extent on different eco-geographic region and crops, remain unclear. This research used cabbage [Brassica pekinensis (Lour.) Rupr.] as the target crop and established as treatment conventional fertilization as a control and a 50% reduction in nitrogen fertilizer at the Yunnan-Guizhou Plateau of China, adding BC or PGPR to evaluate the effects of different treatments on cabbage yield and the soil physicochemical properties. Specifically, high-throughput sequencing probed beneficial soil microbial communities and investigated the impact of BC and PGPR on cabbage yield and soil properties. The results revealed that the soil alkaline hydrolyzable nitrogen (AH-N), available phosphorus (AP), and available potassium (AK) contents were higher in the BC application than in control. The BC application or mixed with PGPR significantly increased the soil organic matter (OM) content (P<0.05), with a maximum of 42.59 g/kg. Further, applying BC or PGPR significantly increased the abundance of beneficial soil microorganisms in the whole growth period of cabbage (P<0.05), such as Streptomyces, Lysobacter, and Bacillus. Meanwhile, the co-application of BC and PGPR increased the abundance of Pseudomonas, and also significantly enhanced the Shannon index and Simpson index of bacterial community (P<0.05). Combined or not with PGPR, the BC application significantly enhanced cabbage yield (P<0.05), with the highest yield reached 1.41 fold of the control. Our research indicated that BC is an suitable and promising carrier of PGPR for soil improvement, combining BC and PGPR can effectively ameliorate the diversity of bacterial community even in acid red soil rhizosphere, and the most direct reflection is to improve soil fertility and cabbage yield.

Whole-Genome Profiling of Endophytic Strain B.L.Ns.14 from Nigella sativa Reveals Potential for Agricultural Bioenhancement

Endophytic microbes in medicinal plants often possess beneficial traits for plant health. This study focuses on the bacterial endophyte strain B.L.Ns.14, isolated from Nigella sativa leaves, which demonstrated multiple plant growth-promoting properties. In vitro tests showed that B.L.Ns.14 supports plant growth, colonization, and tolerance to abiotic stress. The strain also exhibited antifungal activity against phytopathogens such as Rhizoctonia solani, Colletotrichum acutatum, Verticillium dahliae, and Fusarium oxysporum f. sp. radicis-lycopersici. Whole-genome analysis, supported by ANI and dDDH values, identified B.L.Ns.14 as Bacillus halotolerans. Genome mining revealed 128 active carbohydrate enzymes (Cazymes) related to endophytism and biocontrol functions, along with genes involved in phosphate solubilization, siderophore and IAA production, biofilm formation, and motility. Furthermore, genes for osmolyte metabolism, Na+/H+ antiporters, and stress response proteins were also identified. The genome harbors 12 secondary metabolite biosynthetic gene clusters, including those for surfactin, plipastatin mojavensin, rhizocticin A, and bacilysin, known for their antagonistic effects against fungi. Additionally, B.L.Ns.14 promoted Arabidopsis thaliana growth under both normal and saline conditions, and enhanced Solanum lycopersicum growth via seed biopriming and root irrigation. These findings suggest that Bacillus halotolerans B.L.Ns.14 holds potential as a biocontrol and plant productivity agent, warranting further field testing.

Combination of Biogas Residues and Bacillus Interactions Stimulates Crop Production and Salinity Tolerance in Sorghum bicolor

Stress tolerance in cereal crops like Sorghum is important to address food security and land development for saline agriculture. Salinity is considered one of the most devastating abiotic stresses affecting plant growth and yield, specifically in water-scared areas of the world. Biogas residue is a good source of plant nutrients with enriched fertilizer for crop yield and productivity. In this study, seeds were sown in the soil supplied with biogas residues (0% and 5% w/w). After seedling establishment, three Bacillus strains (B26, BS, and BSER) were introduced around the roots of Sorghum. Saline water irrigation started after a week of bacterial inoculation. Sorghum plants were uprooted after 30 days of saline water irrigation. Results indicated that the Bacillus strain and biogas residues showed the highest plant growth in both (0 and 75 mM) salinity levels. Further, this Bacillus strain modulated Sorghum's secondary metabolites (phenols and flavonoids) and osmoprotectants (proline and soluble sugars) under salinity stress. Reduction in salinity stress demonstrated lower activities of antioxidant enzymes including catalase, ascorbate peroxidase, and superoxide dismutase; however, guaiacol peroxidase activities were enhanced in Bacillus (BS strain) treated plants with biogas residues application. Among the three strains, BS strain demonstrated better results with biogas residues under salinity stress in Sorghum bicolor.

Enhancing maize drought and heat tolerance: single vs combined plant growth promoting rhizobacterial inoculation

Maize (Zea mays L.), a key staple crop in Sub-Saharan Africa, is particularly vulnerable to concurrent drought and heat stress, which threatens crop yield and food security. Plant growth-promoting rhizobacteria (PGPR) have shown potential as biofertilizers to enhance plant resilience under such abiotic stresses. This study aimed to (1) identify PGPR isolates tolerant to drought and heat, (2) assess their capacity to mitigate the effects of these stresses on early maize growth, and (3) analyze maize gene expression changes associated with PGPR-induced tolerance. Rhizobacteria were isolated and screened for drought and heat tolerance, alongside key plant growth-promoting (PGP) traits, including phosphorus solubilization, nitrogen fixation, and indole acetic acid production. In vitro and pot trials evaluated the effects of selected isolates on maize growth under stress, using indicators such as shoot length, root and shoot biomass (wet and dry), and leaf water content. Quantitative reverse transcription PCR (qRT-PCR) was employed to profile maize stress response genes. The identified PGPR isolates included Bacillus cereus (11MN1), Bacillus pseudomycoides (21MN1B), Lelliottia amnigena (33MP1), and Leclercia adecarboxylata (36MP8). Greenhouse trials demonstrated that L. amnigena 33MP1, L. adecarboxylata 36MP8, and a mixed culture of isolates (11MN1, 21MN1B, 33MP1, 36MP8) effectively alleviated the adverse effects of concurrent drought and heat stress in maize. Notably, qRT-PCR analysis indicated that PGPR-induced tolerance may involve the modulation of stress response genes CAT2 (catalase 2) and DHN2 (dehydrin 2), which play roles in oxidative stress management and cellular protection. The PGPR isolates identified in this study represent promising bioinoculants for enhancing maize resilience under climate-induced stresses, offering a sustainable approach to improve maize productivity, conserve water, and reduce irrigation needs in drought-prone regions.

Growth regulation in bread wheat via novel bioinoculant formulation

Wheat (Triticum aestivum L.) is one of the most significant crops and the backbone of food security worldwide. However, low wheat production remains a substantial concern in global agricultural systems. It can be attributed to several factors, including adverse climatic conditions, plant disease and poor soil quality. Recent efforts have explored bioinoculant applications as a promising approach to enhance wheat yield, trying to mitigate constraints essential for future wheat production and global food security. This study tested talc powder, wheat biochar, sugarcane bagasse biochar, and farmyard manure as carriers with two endophytic bacterial strains, Burkholderia phytofirmans PsJN and Bacillus spp. MN54 was applied to three wheat varieties (Ujala-16, Zincol-16, and Fathejang-16). The data was recorded at the seedling and maturity growth stages of plants. A pot experiment revealed significant improvements in plant growth following bioinoculant application compared to controls. Notably, the combination of sugarcane bagasse biochar with Bacillus sp. MN54 exhibited the most pronounced effects, promoting internodal length, spike length, tiller number per plant, grain yield per plant, and spikelets per spike. Additionally, talc powder with Bacillus sp. MN54 increased peduncle length, tiller number per plant, and spike length in Fathejang-16. These findings offer valuable insights into optimizing bioinoculant formulations for improved agricultural practices, adapting to climate change, and contributing to ensuring global food security.

Plant growth-promoting rhizobacterium Bacillus megaterium modulates the expression of antioxidant-related and drought-responsive genes to protect rice (Oryza sativa L.) from drought

Global climate change poses a significant threat to plant growth and crop yield and is exacerbated by environmental factors, such as drought, salinity, greenhouse gasses, and extreme temperatures. Plant growth-promoting rhizobacteria (PGPR) help plants withstand drought. However, the mechanisms underlying PGPR-plant interactions remain unclear. Thus, this study aimed to isolate PGPR, Bacillus megaterium strains CACC109 and CACC119, from a ginseng field and investigate the mechanisms underlying PGPR-stimulated tolerance to drought stress by evaluating their plant growth-promoting activities and effects on rice growth and stress tolerance through in vitro assays, pot experiments, and physiological and molecular analyses. Compared with B. megaterium type strain ATCC14581, CACC109 and CACC119 exhibited higher survival rates under osmotic stress, indicating their potential to enhance drought tolerance. Additionally, CACC109 and CACC119 strains exhibited various plant growth-promoting activities, including phosphate solubilization, nitrogen fixation, indole-3-acetic acid production, siderophore secretion, 1-aminocyclopropane-1-carboxylate deaminase activity, and exopolysaccharide production. After inoculation, CACC109 and CACC119 significantly improved the seed germination of rice (Oryza sativa L.) under osmotic stress and promoted root growth under stressed and non-stressed conditions. They also facilitated plant growth in pot experiments, as evidenced by increased shoot and root lengths, weights, and leaf widths. Furthermore, CACC109 and CACC119 improved plant physiological characteristics, such as chlorophyll levels, and production of osmolytes, such as proline. In particular, CACC109- and CACC119-treated rice plants showed better drought tolerance, as evidenced by their higher survival rates, greater chlorophyll contents, and lower water loss rates, compared with mock-treated rice plants. Application of CACC109 and CACC119 upregulated the expression of antioxidant-related genes (e.g., OsCAT, OsPOD, OsAPX, and OsSOD) and drought-responsive genes (e.g., OsWRKY47, OsZIP23, OsDREB2, OsNAC066, OsAREB1, and OsAREB2). In conclusion, CACC109 and CACC119 are promising biostimulants for enhancing plant growth and conferring resistance to abiotic stresses in crop production. Future studies should conduct field trials to validate these findings under real agricultural conditions, optimize inoculation methods for practical use, and further investigate the biochemical and physiological responses underlying the observed benefits.

Plant growth promoting bacteria (PGPB)-induced plant adaptations to stresses: an updated review

Plants and bacteria are co-evolving and interact with one another in a continuous process. This interaction enables the plant to assimilate the nutrients and acquire protection with the help of beneficial bacteria known as plant growth-promoting bacteria (PGPB). These beneficial bacteria naturally produce bioactive compounds that can assist plants' stress tolerance. Moreover, they employ various direct and indirect processes to induce plant growth and protect plants against pathogens. The direct mechanisms involve phytohormone production, phosphate solubilization, zinc solubilization, potassium solubilization, ammonia production, and nitrogen fixation while, the production of siderophores, lytic enzymes, hydrogen cyanide, and antibiotics are included under indirect mechanisms. This property can be exploited to prepare bioformulants for biofertilizers, biopesticides, and biofungicides, which are convenient alternatives for chemical-based products to achieve sustainable agricultural practices. However, the application and importance of PGPB in sustainable agriculture are still debatable despite its immense diversity and plant growth-supporting activities. Moreover, the performance of PGPB varies greatly and is dictated by the environmental factors affecting plant growth and development. This review emphasizes the role of PGPB in plant growth-promoting activities (stress tolerance, production of bioactive compounds and phytohormones) and summarises new formulations and opportunities.

Enhancing spinach (Spinacia oleracea L.) resilience in pesticide-contaminated soil: Role of pesticide-tolerant Ciceribacter azotifigens and Serratia marcescens in root architecture, leaf gas exchange attributes and antioxidant response restoration

This study unveils the detoxification potential of insecticide-tolerant plant beneficial bacteria (PBB), i.e., Ciceribacter azotifigens SF1 and Serratia marcescens SRB1, in spinach treated with fipronil (FIP), profenofos (PF) and chlorantraniliprole (CLP) insecticides. Increasing insecticide doses (25-400 μg kg-1 soil) significantly curtailed germination attributes and growth of spinach cultivated at both bench-scale and in greenhouse experiments. Profenofos at 400 μg kg-1 exhibited maximum inhibitory effects and reduced germination by 55%; root and shoot length by 78% and 81%, respectively; dry matter accumulation in roots and shoots by 79% and 62%, respectively; leaf number by 87% and leaf area by 56%. Insecticide application caused morphological distortion in root tips/surfaces, increased levels of oxidative stress, and cell death in spinach. Application of insecticide-tolerant SF1 and SRB1 strains relieved insecticide pressure resulting in overall improvement in growth and physiology of spinach grown under insecticide stress. Ciceribacter azotifigens improved germination rate (10%); root biomass (53%); shoot biomass (25%); leaf area (10%); Chl-a (45%), Chl-b (36%) and carotenoid (48%) contents of spinach at 25 μg CLP kg-1 soil. PBB inoculation reinvigorated the stressed spinach and modulated the synthesis of phytochemicals, proline, malondialdehyde (MDA), superoxide anions (O2•-), and hydrogen peroxide (H2O2). Scanning electron microscopy (SEM) revealed recovery in root tip morphology and stomatal openings on abaxial leaf surfaces of PBB-inoculated spinach grown with insecticides. Ciceribacter azotifigens inoculation significantly increased intrinsic water use efficiency, transpiration rate, vapor pressure deficit, intracellular CO2 concentration, photosynthetic rate, and stomatal conductance in spinach exposed to 25 μg FIP kg-1. Also, C. azotifigens and S. marcescens modulated the antioxidant defense systems of insecticide-treated spinach. Bacterial strains were strongly colonized to root surfaces of insecticide-stressed spinach seedlings as revealed under SEM. The identification of insecticide-tolerant PBBs such as C. azotifigens and S. marcescens hold the potential for alleviating abiotic stress to spinach, thereby fostering enhanced and safe production within polluted agroecosystems.

Whole Genome Sequencing of Bacillus velezensis AMR25, an Effective Antagonist Strain against Plant Pathogens

The most serious problems for cultivated grapes are pathogenic microorganisms, which reduce the yield and quality of fruit. One of the most widespread disease of grapes is "gray mold", caused by the fungus Botrytis cinerea. Some strains of Bacillus, such as Bacillus halotolerans, Bacillus amyloliquefaciens, and Bacillus velezensis, are known to be active against major post-harvest plant rots. In this study, we showed that the endophytic bacteria B. velezensis strain AMR25 isolated from the leaves of wild grapes Vitis amurensis Rupr. exhibited antimicrobial activity against grape pathogens, including B. cinerea. The genome of B. velezensis AMR25 has one circular chromosome with a length of 3,909,646 bp. with 3689 open reading frames. Genomic analysis identified ten gene clusters involved in the nonribosomal synthesis of polyketides (macrolactin, bacillene, and difficidin), lipopeptides (surfactin, fengycin, and bacillizin), and bacteriocins (difficidin). Also, the genome under study contains a number of genes involved in root colonization, biofilm formation, and biosynthesis of phytohormones. Thus, the endophytic bacteria B. velezensis strain AMR25 shows great promise in developing innovative biological products for enhancing plant resistance against various pathogens.

Green manure application improves insect resistance of subsequent crops through the optimization of soil nutrients and rhizosphere microbiota

Green manure (GM) enhances organic agriculture by improving soil quality and microbiota, yet its effects on plant resistance are unclear. Investigating the GM crop hairy vetch-maize rotation system, a widely adopted GM practice in China, we aimed to determine maize resistance to fall armyworm (FAW), Spodoptera frugiperda (Smith), a major pest. Greenhouse experiments with three fertilization treatments (chemical fertilizer, GM, and a combination) revealed that GM applications significantly improved maize resistance to FAW, evidenced by reduced larval feeding preference and pupal weight. GM also enriched soil nutrients, beneficial rhizobacteria, and resistance-related compounds, such as salicylic acid, jasmonic acid, and 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA), in maize. The results suggest that GM-amended soils and microbial communities may have an underestimated role in regulating host plant adaptation to pests by increasing plant resistance. This study can provide information for developing and implementing environmentally friendly and sustainable cropping systems with enhanced resistance to pests and diseases.

Isolation and identification of Rhizospheric and Endophytic Bacteria from Cucumber plants irrigated with wastewater: Exploring their roles in plant growth promotion and disease suppression

Wastewater contains various emerging contaminants, including heavy metals, residues of pesticides, and pharmaceuticals. Therefore, irrigation with wastewater can enhance heavy metal contamination in soil and adversely affect plant growth. To mitigate this problem, plant growth-promoting bacteria (PGPR) can improve plant growth under heavy metal stress. This study aimed to isolate and characterize rhizospheric and endophytic bacteria from the rhizosphere soil and roots of a cucumber plant irrigated with municipal wastewater. A total of 121 morphologically distinct bacterial isolates from the rhizosphere and 90 bacterial isolates from the endophytic region were isolated and tested for heavy metal resistance and in vitro plant growth-promoting characteristics, including indole-3-acetic acid (IAA) production, phosphate solubilization, Hydrogen Cyanide (HCN) production, and siderophore production. Most of the bacteria analyzed from the rhizospheric and endophytic regions showed various plant growth-promoting characteristics and were tolerant to different heavy metals at various concentrations. Bacterial strains R1 (Proteus sp.) and E2 (Bacillus sp.) were antagonistic to Fusarium oxysporum f. sp. Lycopersici. Wastewater irrigation increases heavy metal-resistant bacteria in cucumber plants, which can alleviate heavy metal stress. Additionally, Proteus sp. and Bacillus sp. isolates are potential candidates for removing heavy metal-contaminated soil and could be potential biofertilizer candidates for selected plants and biocontrol agents.

Cytokinin-deficient Chlamydomonas reinhardtii CRISPR-Cas9 mutants show reduced ability to prime resistance of tobacco against bacterial infection

Although microalgae have only recently been recognized as part of the plant and soil microbiome, their application as biofertilizers has a tradition in sustainable crop production. Under consideration of their ability to produce the plant growth-stimulating hormone cytokinin (CK), known to also induce pathogen resistance, we have assessed the biocontrol ability of CK-producing microalgae. All pro- and eukaryotic CK-producing microalgae tested were able to enhance the tolerance of tobacco against Pseudomonas syringae pv. tabaci (PsT) infection. Since Chlamydomonas reinhardtii (Cre) proved to be the most efficient, we functionally characterized its biocontrol ability. We employed the CRISPR-Cas9 system to generate the first knockouts of CK biosynthetic genes in microalgae. Specifically, we targeted Cre Lonely Guy (LOG) and isopentenyltransferase (IPT) genes, the key genes of CK biosynthesis. While Cre wild-type exhibits a strong protection, the CK-deficient mutants have a reduced ability to induce plant defence. The degree of protection correlates with the CK levels, with the IPT mutants showing less protection than the LOG mutants. Gene expression analyses showed that Cre strongly stimulates tobacco resistance through defence gene priming. This study functionally verifies that Cre primes defence responses with CK, which contributes to the robustness of the effect. This work contributes to elucidate microalgae-mediated plant defence priming and identifies the role of CKs. In addition, these results underscore the potential of CK-producing microalgae as biologicals in agriculture by combining biofertilizer and biocontrol ability for sustainable and environment-friendly crop management.

Novel melatonin-producing Bacillus safensis EH143 mitigates salt and cadmium stress in soybean

Recently, microorganism and exogenous melatonin application has been recognized as an efficient biological tool for enhancing salt tolerance and heavy metal detoxification in agriculture crops. Thus, the goal of this study was to isolate and evaluate a novel melatonin-producing plant growth promoting bacterium. With high-throughput whole genome sequencing, phytohormone measurements, expression profiling, and biochemical analysis, we can identify a novel PGPB that produces melatonin and unravel how it promotes soybean growth and development and protects against salt and Cd stress. We identify the melatonin synthesis pathway (tryptophan→tryptamine→serotonin melatonin) of the halotolerant (NaCl > 800 mM) and heavy metal-resistant (Cd >3 mM) rhizobacterium Bacillus safensis EH143 and use it to treat soybean plants subjected to Cd and NaCl stresses. Results show that EH143 will highly bioaccumulate heavy metals and significantly improve P and Ca2+ uptake and the K+/Na+ (93%↑under salt stress) ratio while reducing Cd uptake (49% under Cd stress) in shoots. This activity was supported by the expression of the ion regulator HKT1, MYPB67, and the calcium sensors CDPK5 and CaMK1 which ultimately led to increased plant growth. EH143 significantly decreased ABA content in shoots by 13%, 20%, and 34% and increased SA biosynthesis in shoots by 14.8%, 31%, and 48.2% in control, salt, and Cd-treated plants, upregulating CYP707A1 and CYP707A2 and PAL1 and ICS, respectively. The melatonin content significantly decreased along with a reduced expression of ASMT3 following treatment with EH143; moreover, reduced expression of peroxidase (POD) and superoxide dismutase (SOD) by 134.5% and 39% under salt+Cd stress, respectively and increased level of total amino acids were observed. Whole-genome sequencing and annotation of EH143 revealed the presence of the melatonin precursor tryptophan synthase (trpA, trpB, trpS), metal and other ion regulators (Cd: cadA, potassium: KtrA and KtrB, phosphate: glpT, calcium: yloB, the sodium/glucose cotransporter: sgIT, and the magnesium transporter: mgtE), and enzyme activators (including the siderophore transport proteins yfiZ and yfhA, the SOD sodA, the catalase katA1, and the glutathione regulator KefG) that may be involved in programming the plant metabolic system. As a consequence, EH143 treatment significantly reduced the contents of lipid peroxidation (O2-, MDA, and H2O2) up to 69%, 46%, and 29% in plants under salt+Cd stress, respectively. These findings suggest that EH143 could be a potent biofertilizer to alleviate NaCl and Cd toxicity in crops and serve as an alternative substitute for exogenous melatonin application.

Exploring the potential of endophyte-plant interactions for improving crop sustainable yields in a changing climate

Climate change poses a major threat to global food security, significantly reducing crop yields as cause of abiotic stresses, and for boosting the spread of new and old pathogens and pests. Sustainable crop management as a route to mitigation poses the challenge of recruiting an array of solutions and tools for the new aims. Among these, the deployment of positive interactions between the micro-biotic components of agroecosystems and plants can play a highly significant role, as part of the agro-ecological revolution. Endophytic microorganisms have emerged as a promising solution to tackle this challenge. Among these, Arbuscular Mycorrhizal Fungi (AMF) and endophytic bacteria and fungi have demonstrated their potential to alleviate abiotic stresses such as drought and heat stress, as well as the impacts of biotic stresses. They can enhance crop yields in a sustainable way also by other mechanisms, such as improving the nutrient uptake, or by direct effects on plant physiology. In this review we summarize and update on the main types of endophytes, we highlight several studies that demonstrate their efficacy in improving sustainable yields and explore possible avenues for implementing crop-microbiota interactions. The mechanisms underlying these interactions are highly complex and require a comprehensive understanding. For this reason, omic technologies such as genomics, transcriptomics, proteomics, and metabolomics have been employed to unravel, by a higher level of information, the complex network of interactions between plants and microorganisms. Therefore, we also discuss the various omic approaches and techniques that have been used so far to study plant-endophyte interactions.

Transcriptomic changes in soybean underlying growth promotion and defense against cyst nematode after Bacillus simplex Sneb545 treatment

Bacillus simplex Sneb45 is a plant-growth-promoting rhizobacterium that promotes soybean growth and systemic resistance to cyst nematode. To investigate transcriptional changes in soybean roots in response to B. simplex Sneb45 treatment, transcriptome analysis and quantitative real-time PCR were conducted to detect and validate the differentially expressed genes (DEGs). In total, 19,109 DEGs were obtained. After B. simplex Sneb545 treatment, 970 and 1265 genes were up- and down-regulated at 5 days post-inoculation (dpi), respectively, and 142 and 47 genes were up- and down-regulated at 10 dpi, respectively, compared with untreated soybean roots. Functional annotation of DEGs indicated that B. simplex Sneb545 regulated soybean growth and defense against cyst nematode possibly through genes related to auxin, gibberellin, and NB-LRR protein. In addition, GO and KEGG enrichment analyses indicated that the DEGs were enriched in metabolism, signal transduction, and plant-pathogen interaction pathways. Moreover, the auxin and gibberellin contents were lower in B. simplex Sneb545-treated soybean roots than in untreated roots at 5 dpi. B. simplex Sneb545 possibly altered the expression of wound-induced protein and NAC transcription factor to regulate soybean growth and defense against cyst nematode. Our study provided deep insights into the alterations in soybean transcriptome after exposure to B. simplex Sneb45 and a theoretical basis for further exploring molecular functions underlying the biological control activity of B. simplex Sneb545.

Dictyophora indusiata and Bacillus aryabhattai improve sugarcane yield by endogenously associating with the root and regulating flavonoid metabolism

Introduction

Endophytes play a significant role in regulating plant root development and facilitating nutrient solubilization and transportation. This association could improve plant growth. The present study has uncovered a distinct phenotype, which we refer to as "white root", arising from the intricate interactions between endophytic fungi and bacteria with the roots in a sugarcane and bamboo fungus (Dictyophora indusiata) intercropping system.

Methods

We investigated the mechanisms underlying the formation of this "white root" phenotype and its impact on sugarcane yield and metabolism by metabarcoding and metabolome analysis.

Results and Discussion

Initial analysis revealed that intercropping with D. indusiata increased sugarcane yield by enhancing the number of viable tillers compared with bagasse and no input control. Metabarcoding based on second-generation and third-generation sequencing indicated that D. indusiate and Bacillus aryabhattai dominates the fungal and bacterial composition in the "white root" phenotype of sugarcane root. The coexistence of D. indusiata and B. aryabhattai as endophytes induced plant growth-promoting metabolites in the sugarcane root system, such as lysoPC 18:1 and dihydrobenzofuran, probably contributing to increased sugarcane yield. Furthermore, the association also enhanced the metabolism of compounds, such as naringenin-7-O-glucoside (Prunin), naringenin-7-O-neohesperidoside (Naringin)*, hesperetin-7-O-neohesperidoside (Neohesperidin), epicatechin, and aromadendrin (Dihydrokaempferol), involved in flavonoid metabolism during the formation of the endophytic phenotype in the sugarcane root system. These observations suggest that the "white root" phenotype promotes sugarcane growth by activating flavonoid metabolism. This study reports an interesting phenomenon where D. indusiata, coordinate with the specific bacteria invade, forms a "white root" phenotype with sugarcane root. The study also provides new insights into using D. indusiata as a soil inoculant for promoting sugarcane growth and proposes a new approach for improve sugarcane cultivation.

Long-Term Benefits of Cenchrus fungigraminus Residual Roots Improved the Quality and Microbial Diversity of Rhizosphere Sandy Soil through Cellulose Degradation in the Ulan Buh Desert, Northwest China

Long-term plant residue retention can effectively replenish soil quality and fertility. In this study, we collected rhizosphere soil from the residual roots of annual Cenchrus fungigraminus in the Ulan Buh Desert over the past 10 years. The area, depth, and length of these roots decreased over time. The cellulose content of the residual roots was significantly higher in the later 5 years (2018-2022) than the former 5 years (2013-2017), reaching its highest value in 2021. The lignin content of the residual roots did not differ across samples except in 2015 and reached its highest level in 2021. The total sugar of the residual roots in 2022 was 227.88 ± 30.69 mg·g-1, which was significantly higher than that in other years. Compared to the original sandy soil, the soil organic matter and soil microbial biomass carbon (SMBC) contents were 2.17-2.41 times and 31.52-35.58% higher in the later 3 years (2020-2022) and reached the highest values in 2020. The residual roots also significantly enhanced the soil carbon stocks from 2018-2022. Soil dehydrogenase, nitrogenase, and N-acetyl-β-D-glucosidase (S-NAG) were significantly affected from 2019-2022. The rhizosphere soil community richness and diversity of the bacterial and fungal communities significantly decreased with the duration of the residual roots in the sandy soil, and there was a significant difference for 10 years. Streptomyces, Bacillus, and Sphigomonas were the representative bacteria in the residual root rhizosphere soil, while Agaricales and Panaeolus were the enriched fungal genera. The distance-based redundancy analysis and partial least square path model results showed that the duration of residual roots in the sandy soil, S-NAG, and SMBC were the primary environmental characteristics that shaped the microbial community. These insights provide new ideas on how to foster the exploration of the use of annual herbaceous plants for sandy soil improvement in the future.

Halotolerant Pseudomonas koreensis S4T10 mitigate salt and drought stress in Arabidopsis thaliana

Salt and drought are documented among the most detrimental and persistent abiotic stresses for crop production. Here, we investigated the impact of Pseudomonas koreensis strain S4T10 on plant performance under salt and drought stress. Arabidopsis thaliana Col-0 wild type and atnced3 mutant plants were inoculated with P. koreensis or tap water and exposed to NaCl (100 mM) for five days and drought stress by withholding water for seven days. P. koreensis significantly enhanced plant biomass and photosynthetic pigments under salt and drought stress conditions. Moreover, P. koreensis activated the antioxidant defence by modulating glutathione (GSH), superoxide dismutase (SOD), peroxidase (POD), and polyphenol oxidase (PPO) activities to scavenge the reactive oxygen species produced due to the stress. In addition, the application of P. koreensis upregulated the expression of genes associated with antioxidant responses, such as AtCAT1, AtCAT3, and AtSOD. Similarly, genes linked to salt stress, such as AtSOS1, AtSOS2, AtSOS3, AtNHX1, and AtHKT1, were also upregulated, affirming the positive role of P. koreensis S4T10 in streamlining the cellular influx and efflux transport systems during salt stress. Likewise, the PGPB inoculation was observed to regulate the expression of drought-responsive genes AtDREB2A, AtDREB2B, and ABA-responsive genes AtAO3, AtABA3 indicating that S4T10 enhanced drought tolerance via modulation of the ABA pathway. The results of this study affirm that P. koreensis S4T10 could be further developed as a biofertilizer to mitigate salt and drought stress at the same time.

The PGPR Bacillus aryabhattai promotes soybean growth via nutrient and chlorophyll maintenance and the production of butanoic acid

Plant growth-promoting rhizobacteria (PGPR) colonize plant roots, establish a mutualistic relationship with the plants and help them grow better. This study reports novel findings on the plant growth-promoting effects of the PGPR Bacillus aryabhattai. Soil was collected from a soybean field, PGPR were isolated, identified, and characterized for their ability to promote plant growth and development. The bacterium was isolated from the soybean rhizosphere and identified as B. aryabhattai strain SRB02 via 16s rRNA sequencing. As shown by SEM, the bacterium successfully colonized rice and soybean roots within 2 days and significantly promoted the growth of the GA-deficient rice cultivar Waito-C within 10 days, as well as the growth of soybean plants with at least six times longer shoots, roots, higher chlorophyll content, fresh, and dry weight after 10 days of inoculation. ICP analysis showed up to a 100% increase in the quantity of 18 different amino acids in the SRB02-treated soybean plants. Furthermore, the 2-DE gel assay indicated the presence of several differentially expressed proteins in soybean leaves after 24 hrs of SRB02 application. MALDI-TOF-MS identified β-conglycinin and glycinin along with several other proteins that were traced back to their respective genes. Analysis of bacterial culture filtrates via GCMS recorded significantly higher quantities of butanoic acid which was approximately 42% of all the metabolites found in the filtrates. The application of 100 ppm butanoic acid had significantly positive effects on plant growth via chlorophyll maintenance. These results establish the suitability of B. aryabhattai as a promising PGPR for field application in various crops.

Unveiling the dynamic relationship of viruses and/or symbiotic bacteria with plant resilience in abiotic stress

In the ecosphere, plants interact with environmental biotic and abiotic partners, where unbalanced interactions can induce unfavourable stress conditions. Abiotic factors (temperature, water, and salt) are primarily required for plants healthy survival, and any change in their availability is reflected as a stress signal. In certain cases, the presence of infectious pathogens such as viruses, bacteria, fungi, protozoa, nematodes, and insects can also create stress conditions in plants, leading to the emergence of disease or deficiency symptoms. While these symptoms are often typical of abiotic or biotic stress, however, there are instances where they can intensify under specific conditions. Here, we primarily summarize the viral interactions with plants during abiotic stress to understand how these associations are linked together during viral pathogenesis. Secondly, focus is given to the beneficial effects of root-associated symbiotic bacteria in fulfilling the basic needs of plants during normal as well as abiotic stress conditions. The modulations of plant functional proteins, and their occurrence/cross-talk, with pathogen (virus) and symbiont (bacteria) molecules are also discussed. Furthermore, we have highlighted the biochemical and systematic adaptations that develop in plants due to bacterial symbiosis to encounter stress hallmarks. Lastly, directions are provided towards exploring potential rhizospheric bacteria to maintain plant-microbes ecosystem and manage abiotic stress in plants to achieve better trait health in the horticulture crops.

Rhizobacteria Bacillus spp. mitigate osmotic stress and improve seed germination in mustard by regulating osmolyte and plant hormone signaling

Drought, a widespread abiotic stressor, exerts a profound impact on agriculture, impeding germination and plant growth, and reducing crop yields. In the present investigation, the osmotolerant rhizobacteria Bacillus casamancensis strain MKS-6 and Bacillus sp. strain MRD-17 were assessed for their effects on molecular processes involved in mustard germination under osmotic stress conditions. Enhancement in germination was evidenced by improved germination percentages, plumule and radicle lengths, and seedling vigor upon rhizobacterial inoculation under no stress and osmotic stress conditions. Under osmotic stress, rhizobacteria stimulated the production of gibberellins and reserve hydrolytic enzymes (lipases, isocitrate lyase, and malate synthase), bolstering germination. Furthermore, these rhizobacteria influenced the plant hormones such as gibberellins and abscisic acid (ABA), as well as signalling pathways, thereby promoting germination under osmotic stress. Reduced proline and glycine betaine accumulation, and down-regulation of transcription factors BjDREB1_2 and BjDREB2 (linked to ABA-independent signalling) in rhizobacteria-inoculated seedlings indicated that bacterial treatment mitigated water deficit stress during germination, independently of these pathways. Hence, the advantageous attributes exhibited by these rhizobacterial strains can be effectively harnessed to alleviate drought-induced stress in mustard crops, potentially through the development of targeted bio-formulations.

The Contribution of Hormonal Changes to the Protective Effect of Endophytic Bacterium Bacillus subtilis on Two Wheat Genotypes with Contrasting Drought Sensitivities under Osmotic Stress

A comparative analysis was conducted to evaluate the effects of seed priming with endophytic bacterium Bacillus subtilis 10-4 (BS) on the hormonal system and cell wall tolerance (lipid peroxidation (LPO), electrolyte leakage (EL), and root lignin deposition) of two Triticum aestivum L. (wheat) varieties with contrasting drought sensitivities (Ekada 70-drought-tolerant (DT); Salavat Yulaev-drought-sensitive (DS)) under normal conditions and 12% polyethylene glycol-6000 (PEG)-induced osmotic stress. The results showed that under normal conditions, the growth stimulation in wheat plants by BS was attributed to changes in the hormonal balance, particularly an increase in endogenous indole-3-acetic acid (IAA) accumulation. However, under stress, a significant hormonal imbalance was observed in wheat seedlings, characterized by a pronounced accumulation of abscisic acid (ABA) and a decrease in the levels of IAA and cytokinins (CK). These effects were reflected in the inhibition of plant growth. BS exhibited a protective effect on stressed plants, as evidenced by a significantly lower amplitude of stress-induced changes in the hormonal system: maintaining the content of IAA at a level close to the control, reducing stress-induced ABA accumulation, and preventing CK depletion. These effects were further reflected in the normalization of growth parameters in dehydrated seedlings, as well as a decrease in leaf chlorophyll degradation, LPO, and EL, along with an increase in lignin deposition in the basal part of the roots in both genotypes. Overall, the findings demonstrate that BS, producing phytohormones, specifically IAA and ABA, had a more pronounced protective effect on DT plants, as evidenced by a smaller amplitude of stress-induced hormonal changes, higher leaf chlorophyll content, root lignin deposition, and lower cell membrane damage (LPO) and permeability (EL) compared to DS plants.

Marvels of Bacilli in soil amendment for plant-growth promotion toward sustainable development having futuristic socio-economic implications

Microorganisms are integral components of ecosystems, exerting profound impacts on various facets of human life. The recent United Nations General Assembly (UNGA) Science Summit emphasized the critical importance of comprehending the microbial world to address global challenges, aligning with the United Nations Sustainable Development Goals (SDGs). In agriculture, microbes are pivotal contributors to food production, sustainable energy, and environmental bioremediation. However, decades of agricultural intensification have boosted crop yields at the expense of soil health and microbial diversity, jeopardizing global food security. To address this issue, a study in West Bengal, India, explored the potential of a novel multi-strain consortium of plant growth promoting (PGP) Bacillus spp. for soil bioaugmentation. These strains were sourced from the soil's native microbial flora, offering a sustainable approach. In this work, a composite inoculum of Bacillus zhangzhouensis MMAM, Bacillus cereus MMAM3), and Bacillus subtilis MMAM2 were introduced into an over-exploited agricultural soil and implications on the improvement of vegetative growth and yield related traits of Gylcine max (L) Meril. plants were evaluated, growing them as model plant, in pot trial condition. The study's findings demonstrated significant improvements in plant growth and soil microbial diversity when using the bacterial consortium in conjunction with vermicompost. Metagenomic analyses revealed increased abundance of many functional genera and metabolic pathways in consortium-inoculated soil, indicating enhanced soil biological health. This innovative bioaugmentation strategy to upgrade the over-used agricultural soil through introduction of residual PGP bacterial members as consortia, presents a promising path forward for sustainable agriculture. The rejuvenated patches of over-used land can be used by the small and marginal farmers for cultivation of resilient crops like soybean. Recognizing the significance of multi-strain PGP bacterial consortia as potential bioinoculants, such technology can bolster food security, enhance agricultural productivity, and mitigate the adverse effects of past agricultural activities.

Applications and Market of Micro-Organism-Based and Plant-Based Inputs in Brazilian Agriculture

The use of plant-based and micro-organism-based biological inputs is a sustainable agricultural practice. It promotes a suitable and better utilization of non-renewable resources in the environment. The benefits of using micro-organisms are associated with direct and indirect mechanisms, mainly related to improvements in the absorption and availability of nutrients, resulting in a consequent impact on plant growth. The main benefits of using biochemical pesticides are the promotion of sustainability and the management of resistance to pests and diseases. Although the use of micro-organisms and botanical metabolites is a promising agricultural alternative, they are still primarily concentrated in grain crops. There is a huge opportunity to expand the plant-based and micro-organism-based biological inputs used in agriculture due to the wide range of mechanisms of action of those products. At a global level, several terminologies have been adopted to characterize biological inputs, but many terms used conflict with Brazilian legislation. This review will clarify the classes of biological inputs existing in Brazil as well as present the application and evolution of the market for microbiological and plant-based inputs.

Bacillus spp. as Bio-factories for Antifungal Secondary Metabolites: Innovation Beyond Whole Organism Formulations

Several fungi act as parasites for crops causing huge annual crop losses at both pre- and post-harvest stages. For years, chemical fungicides were the solution; however, their wide use has caused environmental contamination and human health problems. For this reason, the use of biofungicides has been in practice as a green solution against fungal phytopathogens. In the context of a more sustainable agriculture, microbial biofungicides have the largest share among the commercial biocontrol products that are available in the market. Precisely, the genus Bacillus has been largely studied for the management of plant pathogenic fungi because they offer a chemically diverse arsenal of antifungal secondary metabolites, which have spawned a heightened industrial engrossment of it as a biopesticide. In this sense, it is indispensable to know the wide arsenal that Bacillus genus has to apply these products for sustainable agriculture. Having this idea in our minds, in this review, secondary metabolites from Bacillus having antifungal activity are chemically and structurally described giving details of their action against several phytopathogens. Knowing the current status of Bacillus secreted antifungals is the base for the goal to apply these in agriculture and it is addressed in depth in the second part of this review.

Signaling and crosstalk of rhizobacterial and plant hormones that mediate abiotic stress tolerance in plants

Agricultural areas exhibiting numerous abiotic stressors, such as elevated water stress, temperatures, and salinity, have grown as a result of climate change. As such, abiotic stresses are some of the most pressing issues in contemporary agricultural production. Understanding plant responses to abiotic stressors is important for global food security, climate change adaptation, and improving crop resilience for sustainable agriculture, Over the decades, explorations have been made concerning plant tolerance to these environmental stresses. Plant growth-promoting rhizobacteria (PGPR) and their phytohormones are some of the players involved in developing resistance to abiotic stress in plants. Several studies have investigated the part of phytohormones in the ability of plants to withstand and adapt to non-living environmental factors, but very few have focused on rhizobacterial hormonal signaling and crosstalk that mediate abiotic stress tolerance in plants. The main objective of this review is to evaluate the functions of PGPR phytohormones in plant abiotic stress tolerance and outline the current research on rhizobacterial hormonal communication and crosstalk that govern plant abiotic stress responses. The review also includes the gene networks and regulation under diverse abiotic stressors. The review is important for understanding plant responses to abiotic stresses using PGPR phytohormones and hormonal signaling. It is envisaged that PGPR offer a useful approach to increasing plant tolerance to various abiotic stresses. However, further studies can reveal the unclear patterns of hormonal interactions between plants and rhizobacteria that mediate abiotic stress tolerance.

Bacillus velezensis Strain HN-Q-8 Induced Resistance to Alternaria solani and Stimulated Growth of Potato Plant

Bacillus velezensis HN-Q-8, isolated in our previous study, has an antagonistic effect on Alternaria solani. After being pretreated with a fermentation liquid with HN-Q-8 bacterial cell suspensions, the potato leaves inoculated with A. solani displayed smaller lesion areas and less yellowing than the controls. Interestingly, the activity levels of superoxide dismutase, peroxidase, and catalase in potato seedlings were enhanced by the addition of the fermentation liquid with bacterial cells. Additionally, the overexpression of key genes related to induced resistance in the Jasmonate/Ethylene pathway was activated by the addition of the fermentation liquid, suggesting that the HN-Q-8 strain induced resistance to potato early blight. In addition, our laboratory and field experiments showed that the HN-Q-8 strain can promote potato seedling growth and significantly increase tuber yield. The root activity and chlorophyll content of potato seedlings were significantly increased along with the levels of indole acetic acid, gibberellic acid 3, and abscisic acid upon addition of the HN-Q-8 strain. The fermentation liquid with bacterial cells was more efficient in inducing disease resistance and promoting growth than bacterial cell suspensions alone or the fermentation liquid without bacterial cells. Thus, the B. velezensis HN-Q-8 strain is an effective bacterial biocontrol agent, augmenting the options available for potato cultivation.

Plant Growth-Promoting Rhizobacteria (PGPR) with Microbial Growth Broth Improve Biomass and Secondary Metabolite Accumulation of Cannabis sativa L

Plant growth-promoting rhizobacteria (PGPR) are a sustainable crop production input; some show positive effects under laboratory conditions but poorly colonize host field-grown plants. Inoculating with PGPR in microbial growth medium (e.g., King's B) could overcome this. We evaluated cannabis plant (cv. CBD Kush) growth promotion by inoculating three PGPR (Bacillus sp., Mucilaginibacter sp., and Pseudomonas sp.) in King's B at vegetative and flower stages. At the vegetative stage, Mucilaginibacter sp. inoculation increased flower dry weight (24%), total CBD (11.1%), and THC (11.6%); Pseudomonas sp. increased stem (28%) dry matter, total CBD (7.2%), and THC (5.9%); and Bacillus sp. increased total THC by 4.8%. Inoculation with Mucilaginibacter sp. and Pseudomonas sp. at the flowering stage led to 23 and 18% increases in total terpene accumulation, respectively. Overall, vegetative inoculation with PGPR enhanced cannabis yield attributes and chemical profiles. Further research into PGPR inoculation onto cannabis and the subsequent level of colonization could provide key insights regarding PGPR-host interactions.

Influence of Thermotolerant Rhizobacteria Bacillus spp. on Biochemical Attributes and Antioxidant Status of Mustard Under High Temperature Stress

Due to global warming, increasing incidences of higher-than-normal temperatures have been observed, which adversely affect seed germination, crop growth, and productivity. Several reports are available on the effect of inoculation with rhizobacteria on plant growth and biochemical attributes; however, information on their influence on seed germination and plant stress levels is lacking. In the present study, under heat stress, we studied the effect of three thermotolerant rhizobacterial strains on mustard seed germination, seedling vigor, and plant growth. Effect of inoculation with the rhizobacterial strains on the plant stress levels, biochemical attributes and antioxidant activity was also determined. Under heat stress, inoculation with the rhizobacterial strains improved seed germination and seedling fresh weight and plumule length; while only Bacillus licheniformis SSA 61 inoculated plants showed better radicle length. There was a concomitant decrease in the plant ethylene levels in the inoculated treatments. Inoculated plants showed higher shoot fresh weight, however, Bacillus sp. MRD-17 inoculated plants only improved root growth. There was significant increase in most of the plant biochemical parameters and activities of antioxidant enzymes superoxide dismutase, catalase, and ascorbate peroxidase. Significant reduction in proline and total sugar content was noted in the inoculated treatments; while increase in the amino acid and phenolics content was observed. A further increase in the antioxidant enzyme activity was recorded in most of the inoculated treatments compared with no stress. Thus, our study indicated that thermotolerant rhizobacterial strains reduced plant stress levels; enhanced seed germination, seedling vigor, plant biomass, and thermotolerance of mustard.

Metal-tolerant and siderophore producing Pseudomonas fluorescence and Trichoderma spp. improved the growth, biochemical features and yield attributes of chickpea by lowering Cd uptake

Industrialization and human urbanization have led to an increase in heavy metal (HM) pollution which often cause negative/toxic effect on agricultural crops. The soil-HMs cannot be degraded biologically however, microbe-mediated detoxification of toxic HMs into lesser toxic forms are reported. Considering the potentiality of HMs-tolerant soil microbes in metal detoxification, Pseudomonas fluorescence PGPR-7 and Trichoderma sp. T-4 were recovered from HM-affected areas. Under both normal and cadmium stress, the ability of both microorganisms to produce different plant hormones and biologically active enzymes was examined. Strains PGPR-7 and T-4 tolerated cadmium (Cd) an up-to 1800 and 2000 µg mL^-1, respectively, and produced various plant growth regulating substances (IAA, siderophore, ACC deaminase ammonia and HCN) in Cd-stressed condition. The growth promoting and metal detoxifying ability of both strains were evaluated (either singly/combined) by applying them in chickpea (Cicer arietinum L.) plants endogenously contaminated with different Cd levels (0-400 µg kg^-1 soils). The higher Cd concentration (400 µg kg^-1 soils) negatively influenced the plant parameters which, however, improved following single/combined inoculation of P. fluorescence PGPR-7 and Trichoderma sp. T-4. Both microbial strains increased the growth of Cd-treated chickpeas however, their combined inoculation (PGPR-7 + T-4) caused the most positive effect. For instance, 25 µg Cd Kg^-1 + PGPR-7 + T4 treatment caused maximum increase in germination percentage (10%), root dry biomass (71.4%) and vigour index (33%), chl-a (38%), chl-b (41%) and carotenoid content (52%). Furthermore, combined inoculation of P. fluorescence PGPR-7 and Trichoderma sp. T-4 maximally decreased the proline, MDA content, POD and CAT activities by 50%, 43% and 62%, respectively following their application in 25 µg Cd kg^-1 soils-treated chickpea. Additionally, microbial strains lowered the plant uptake of Cd. For example, Cd-uptake in root tissues was decreased by 42 and 34% when 25 µg Cd Kg^-1- treated chickpea plants were inoculated with P. fluorescence PGPR-7, Trichoderma sp. T-4 and co-inoculation (PGPR-7 + T4) of both strains, respectively. Therefore, from the current observation, it is suggested that dual inoculation of metal tolerant P. fluorescence and Trichoderma sp. may potentially be used in detoxification and reclamation of metal-contaminated soils.

Physiological and molecular insight of microbial biostimulants for sustainable agriculture

Increased food production to cater the need of growing population is one of the major global challenges. Currently, agro-productivity is under threat due to shrinking arable land, increased anthropogenic activities and changes in the climate leading to frequent flash floods, prolonged droughts and sudden fluctuation of temperature. Further, warm climatic conditions increase disease and pest incidences, ultimately reducing crop yield. Hence, collaborated global efforts are required to adopt environmentally safe and sustainable agro practices to boost crop growth and productivity. Biostimulants appear as a promising means to improve growth of plants even under stressful conditions. Among various categories of biostimulants, microbial biostimulants are composed of microorganisms such as plant growth-promoting rhizobacteria (PGPR) and/or microbes which stimulate nutrient uptake, produce secondary metabolites, siderophores, hormones and organic acids, participate in nitrogen fixation, imparts stress tolerance, enhance crop quality and yield when applied to the plants. Though numerous studies convincingly elucidate the positive effects of PGPR-based biostimulants on plants, yet information is meagre regarding the mechanism of action and the key signaling pathways (plant hormone modulations, expression of pathogenesis-related proteins, antioxidants, osmolytes etc.) triggered by these biostimulants in plants. Hence, the present review focuses on the molecular pathways activated by PGPR based biostimulants in plants facing abiotic and biotic challenges. The review also analyses the common mechanisms modulated by these biostimulants in plants to combat abiotic and biotic stresses. Further, the review highlights the traits that have been modified through transgenic approach leading to physiological responses akin to the application of PGPR in the target plants.

Bioinoculant mediated regulation of signalling cascades in various stress responses in plants

Bio-inoculation involves the association of plant with some beneficial microorganisms, and among these microbiotas, those bacteria which can promote plant growth and development are known as Plant Growth Promoting Rhizobacteria (PGPR). It can help a plant directly or indirectly, which includes root development, biological nitrogen (N₂) fixation, stress tolerance, cell division and elongation, solubilization of Zinc, Phosphate, Potassium, soil health improvement and many more. PGPR have gained attention as it can be used as biofertilizers and helpful in bioremediation techniques, which in turn can reduce the chemical dependency in agriculture. PGPR mediated plant growth and stress management is developed by the virtue of the interaction of plant and microbial signalling pathways. On the other hand, environmental stresses are something to which a plant is always exposed irrespective of other factors. The present review is all about the better understanding of the convergence strategies of these signalling molecules and the ambiguities of signalling activities occurring in the host due to the interaction with PGPR under environmental stressed conditions.

Silicon and soil microorganisms improve rhizospheric soil health with bacterial community, plant growth, performance and yield

The interaction of silicon and soil microorganisms stimulates crop enhancement to ensure sustainable agriculture. Silicon may potentially increase nutrient availability in rhizosphere with improved plants' growth, development as it does not produce phytotoxicity. The rhizospheric microbiome accommodates a variety of microbial species that live in a small area of soil directly associated with the hidden half plants' system. Plant growth-promoting rhizobacteria (PGPR) play a major role in plant development in response to adverse climatic conditions. PGPRs may enhance the growth, quality, productivity in variety of crops, and mitigate abiotic stresses by reprogramming stress-induced physiological variations in plants via different mechanisms, such as synthesis of indole-3-acetic acid, 1-aminocyclopropane-1-carboxylate deaminase, exopolysaccharides, volatile organic compounds, atmospheric nitrogen fixation, and phosphate solubilization. Our article eye upon interactions of silicon and plant microbes which seems to be an opportunity for sustainable agriculture for series of crops and cropping systems in years to come, essential to safeguard the food security for masses.

Exploration of the rhizosphere microbiome of native plant Ceanothus velutinus - an excellent resource of plant growth-promoting bacteria

Continuous demand for an increase in food production due to climate change and a steady rise in world population requires stress-resilient, sustainable agriculture. Overuse of chemical fertilizers and monoculture farming to achieve this goal deteriorated soil health and negatively affected its microbiome. The rhizosphere microbiome of a plant plays a significant role in its growth and development and promotes the plant's overall health through nutrient uptake/availability, stress tolerance, and biocontrol activity. The Intermountain West (IW) region of the US is rich in native plants recommended for low water use landscaping because of their drought tolerance. The rhizosphere microbiome of these native plants is an excellent resource for plant growth-promoting rhizobacteria (PGPR) to use these microbes as biofertilizers and biostimulants to enhance food production, mitigate environmental stresses and an alternative for chemical fertilizer, and improve soil health. Here, we isolated, purified, identified, and characterized 64 bacterial isolates from a native plant, Ceanothus velutinus, commonly known as snowbrush ceanothus, from the natural habitat and the greenhouse-grown native soil-treated snowbrush ceanothus plants. We also conducted a microbial diversity analysis of the rhizosphere of greenhouse-grown native soil-treated and untreated plants (control). Twenty-seven of the 64 isolates were from the rhizosphere of the native region, and 36 were from the greenhouse-grown native soil-treated plants. These isolates were also tested for plant growth-promoting (PGP) traits such as their ability to produce catalase, siderophore, and indole acetic acid, fix atmospheric nitrogen and solubilize phosphate. Thirteen bacterial isolates tested positive for all five plant growth-promoting abilities and belonged to the genera Pantoea, Pseudomonas, Bacillus, and Ancylobacter. Besides, there are isolates belonging to the genus Streptomyces, Bacillus, Peribacillus, Variovorax, Xenophilus, Brevundimonas, and Priestia, which exhibit at least one of the plant growth-promoting activities. This initial screen provided a list of potential PGPR to test for plant health improvement on model and crop plants. Most of the bacterial isolates in this study have a great potential to become biofertilizers and bio-stimulants.

Bacillus spp. as Bioagents: Uses and Application for Sustainable Agriculture

Food security will be a substantial issue in the near future due to the expeditiously growing global population. The current trend in the agriculture industry entails the extravagant use of synthesized pesticides and fertilizers, making sustainability a difficult challenge. Land degradation, lower production, and vulnerability to both abiotic and biotic stresses are problems caused by the usage of these pesticides and fertilizers. The major goal of sustainable agriculture is to ameliorate productivity and reduce pests and disease prevalence to such a degree that prevents large-scale damage to crops. Agriculture is a composite interrelation among plants, microbes, and soil. Plant microbes play a major role in growth promotion and improve soil fertility as well. Bacillus spp. produces an extensive range of bio-chemicals that assist in plant disease control, promote plant development, and make them suitable for agricultural uses. Bacillus spp. support plant growth by N fixation, P and K solubilization, and phytohormone synthesis, in addition to being the most propitious biocontrol agent. Moreover, Bacilli excrete extracellular metabolites, including antibiotics, lytic enzymes, and siderophores, and demonstrate antagonistic activity against phytopathogens. Bacillus spp. boosts plant resistance toward pathogens by inducing systemic resistance (ISR). The most effective microbial insecticide against insects and pests in agriculture is Bacillus thuringiensis (Bt). Additionally, the incorporation of toxin genes in genetically modified crops increases resistance to insects and pests. There is a constant increase in the identified Bacillus species as potential biocontrol agents. Moreover, they have been involved in the biosynthesis of metallic nanoparticles. The main objective of this review article is to display the uses and application of Bacillus specie as a promising biopesticide in sustainable agriculture. Bacillus spp. strains that are antagonistic and promote plant yield attributes could be valuable in developing novel formulations to lead the way toward sustainable agriculture.

Changes of endophytic microbial community in Rhododendron simsii roots under heat stress and its correlation with leaf physiological indicators

Introduction

The response mechanism of Rhododendron simsii and its endophytic microorganism to heat stress is still unclear.

Methods

The light incubator was used to set the temperature gradients, and the control (CK) was (day/night: 14/10 h) 25/22°C, the moderate-heat-stress (MHS) was 35/30°C and the high-heat-stress (HHS) was 40/35°C.

Results

Compared with CK, MHS significantly increased the contents of malondialdehyde, hydrogen peroxide, proline, and soluble sugar, as well as the activities of catalase and peroxidase in leaf, while HHS increased the activities of ascorbate peroxidase, and decreased chlorophyll content. Compared with CK, MHS reduced soil available nitrogen (N) content. Both heat stress changed the endophytic microbial community structure in roots. MHS enriched Pezicula and Paracoccus, while HHS significantly enriched Acidothermus and Haliangium. The abundance of Pezicula positively correlated with the contents of chlorophyll a and proline in leaf, and negatively correlated with soil ammonium N content. The abundance of Pezicula and Haliangium positively correlated with soluble sugar and malondialdehyde contents, respectively.

Conclusions

Our results suggest that root endophytic microorganisms play an important role in helping Rhododendron resisting heat stress, mainly by regulating soil N content and plant physiological characteristics.

The Importance of Microorganisms for Sustainable Agriculture-A Review

In the face of climate change, progressive degradation of the environment, including agricultural land negatively affecting plant growth and development, endangers plant productivity. Seeking efficient and sustainable agricultural techniques to replace agricultural chemicals is one of the most important challenges nowadays. The use of plant growth-promoting microorganisms is among the most promising approaches; however, molecular mechanisms underneath plant-microbe interactions are still poorly understood. In this review, we summarized the knowledge on plant-microbe interactions, highlighting the role of microbial and plant proteins and metabolites in the formation of symbiotic relationships. This review covers rhizosphere and phyllosphere microbiomes, the role of root exudates in plant-microorganism interactions, the functioning of the plant's immune system during the plant-microorganism interactions. We also emphasized the possible role of the stringent response and the evolutionarily conserved mechanism during the established interaction between plants and microorganisms. As a case study, we discussed fungi belonging to the genus Trichoderma. Our review aims to summarize the existing knowledge about plant-microorganism interactions and to highlight molecular pathways that need further investigation.

Bacillus aryabhattai LAD impacts rhizosphere bacterial community structure and promotes maize plant growth

BACKGROUND

Plant growth-promoting rhizobacteria may significantly impact the soil microbial community and the growth of plant roots and have critical roles in soil ecosystem functioning. However, the interactions between rhizobacteria and plants are extremely complicated and remain understudied.

RESULTS

In this study, a Bacillus strain was isolated from a long-term maize colonization soil and identified as Bacillus aryabhattai strain LAD. Laboratory tests showed that B. aryabhattai LAD had phosphate-solubilizing and nitrogen-fixing functions that benefit plant growth. The effects of LAD cultures on the root system development of corn seedlings and the structure of rhizosphere bacterial communities were studied. The most significant stimulations of LAD culture on plant growth were observed at a cell density of 10²  CFU mL^-1 . Treatment with LAD culture in hydroponics caused an increase of 107%, 197%, and 25% in the shoot length, total root length, and main root thickness respectively. The LAD treatment also significantly affected the rhizosphere microbial abundance and community structure. The rhizobacterial abundance and species richness in the corn seedlings treated with LAD culture were significantly lower than those in the control group. However, the LAD-treated samples had higher relative abundances of plant growth-promoting rhizobacteria like Bacillus and Burkholderia than the control samples did, suggesting that LAD treatment may facilitate the mutualistic relation between the rhizosphere microbiome and the plant.

CONCLUSION

These results collectively demonstrated that LAD is capable of shaping the rhizosphere microbial community structure and functions as a plant growth-promoting agent, which makes it a strong candidate for application as bio-fertilizer in agricultural systems. © 2022 Society of Chemical Industry.

Molecular mechanisms of plant growth promotion for methylotrophic Bacillus aryabhattai LAD

Plant growth-promoting rhizobacteria (PGPR) can produce hormone-like substances, promote plant nutrient uptake, enhance plant resistance, inhibit the growth of pathogenic bacteria, and induce plant resistance to biotic and abiotic stresses. Bacillus is one of the most studied genera that promote plant root development. Since its discovery in 2009, B. aryabhattai has shown promising properties such as promoting plant growth and improving crop yield. However, the mechanisms of B. aryabhattai promoting plant growth remain to be investigated. In this study, the chromosome of B. aryabhattai strain LAD and five plasmids within the cell were sequenced and annotated. The genome, with a length of 5,194,589 bp and 38.12% GC content, contains 5,288 putative protein-coding genes, 39 rRNA, and 112 tRNA. The length of the five plasmids ranged from 116,519 to 212,484 bp, and a total of 810 putative protein-coding genes, 4 rRNA, and 32 tRNA were predicted in the plasmids. Functional annotation of the predicted genes revealed numerous genes associated with indole-3 acetic acid (IAA) and exopolysaccharides (EPSs) biosynthesis, membrane transport, nitrogen cycle metabolism, signal transduction, cell mobility, stress response, and antibiotic resistance on the genome which benefits the plants. Genes of carbohydrate-active enzymes were detected in both the genome and plasmids suggesting that LAD has the capacity of synthesizing saccharides and utilizing organic materials like root exudates. LAD can utilize different carbon sources of varied carbon chain length, i.e., methanol, acetate, glycerol, glucose, sucrose, and starch for growth and temperature adaptation suggesting a high versatility of LAD for thriving in fluctuating environments. LAD produced the most EPSs with sucrose as sole carbon source, and high concentration of IAA was produced when the maize plant was cultivated with LAD, which may enhance plant growth. LAD significantly stimulated the development of the maize root. The genome-based information and experimental evidence demonstrated that LAD with diverse metabolic capabilities and positive interactions with plants has tremendous potential for adaptation to the dynamic soil environments and promoting plant growth.

Effects of Bradyrhizobium Co-Inoculated with Bacillus and Paenibacillus on the Structure and Functional Genes of Soybean Rhizobacteria Community

Plant growth-promoting rhizobacteria (PGPR) are widely used to improve soil nutrients and promote plant growth and health. However, the growth-promoting effect of a single PGPR on plants is limited. Here, we evaluated the effect of applying rhizobium Bradyrhizobium japonicum 5038 (R5038) and two PGPR strains, Bacillus aryabhattai MB35-5 (BA) and Paenibacillus mucilaginosus 3016 (PM), alone or in different combinations on the soil properties and rhizosphere bacterial community composition of soybean (Glycine max). Additionally, metagenomic sequencing was performed to elucidate the profile of functional genes. Inoculation with compound microbial inoculant containing R5038 and BA (RB) significantly improved nodule nitrogenase activity and increased soil nitrogen content, and urease activity increased the abundance of the nitrogen cycle genes and Betaproteobacteria and Chitinophagia in the rhizosphere. In the treatment of inoculant-containing R5038 and PM (RP), significant changes were found for the abundance of Deltaproteobacteria and Gemmatimonadetes and the phosphorus cycle genes, and soil available phosphorus and phosphatase activity were increased. The RBP inoculants composed of three strains (R5038, BA and PM) significantly affected soybean biomass and the N and P contents of the rhizosphere. Compared with RB and RP, RBP consistently increased soybean nitrogen content, and dry weight. Overall, these results showed that several PGPR with different functions could be combined into composite bacterial inoculants, which coordinately modulate the rhizosphere microbial community structure and improve soybean growth.

Dual Inoculation of Plant Growth-Promoting Bacillus endophyticus and Funneliformis mosseae Improves Plant Growth and Soil Properties in Ginger

Co-inoculation with beneficial microbes has been suggested as a useful practice for the enhancement of plant growth, nutrient uptake, and soil nutrients. For the first time in Uzbekistan the role of plant-growth-promoting Bacillus endophyticus IGPEB 33 and arbuscular mycorrhizal fungi (AMF) on plant growth, the physiological properties of ginger (Zingiber officinale), and soil enzymatic activities was studied. Moreover, the coinoculation of B. endophyticus IGPEB 33 and AMF treatment significantly increased the plant height by 81%, leaf number by 70%, leaf length by 82%, and leaf width by 40% compared to the control. B. endophyticus IGPEB 33 individually increased plant height significantly by 51%, leaf number by 56%, leaf length by 67%, and leaf width by 27% as compared to the control treatment. Compared to the control, B. endophyticus IGPEB 33 and AMF individually significantly increased chlorophyll a by 81-58%, chlorophyll b by 68-37%, total chlorophyll by 74-53%, and carotenoid content by 67-55%. However, combination of B. endophyticus IGPEB 33 and AMF significantly increased chlorophyll a by 86%, chlorophyll b by 72%, total chlorophyll by 82%, and carotenoid content by 83% compared to the control. Additionally, plant-growth-promoting B. endophyticus IGPEB 33 and AMF inoculation improved soil nutrients and soil enzyme activities compared to the all treatments. Co-inoculation with plant-growth-promoting B. endophyticus and AMF could be an alternative for the production of ginger that is more beneficial to soil nutrient deficiencies. We suggest that a combination of plant-growth-promoting B. endophyticus and AMF inoculation could be a more sustainable and eco-friendly approach in a nutrient-deficient soil.

Bacillus for Plant Growth Promotion and Stress Resilience: What Have We Learned?

The rhizosphere is a thin film of soil that surrounds plant roots and the primary location of nutrient uptake, and is where important physiological, chemical, and biological activities are occurring. Many microbes invade the rhizosphere and have the capacity to promote plant growth and health. Bacillus spp. is the most prominent plant growth promoting rhizobacteria due to its ability to form long-lived, stress-tolerant spores. Bacillus-plant interactions are driven by chemical languages constructed by a wide spectrum of metabolites and lead to enhanced plant growth and defenses. Thus, this review is a synthesis and a critical assessment of the current literature on the application of Bacillus spp. in agriculture, highlighting gaps that remain to be explored to improve and expand on the Bacillus-based biostimulants. Furthermore, we suggest that omics sciences, with a focus on metabolomics, offer unique opportunities to illuminate the chemical intercommunications between Bacillus and plants, to elucidate biochemical and molecular details on modes of action of Bacillus-based formulations, to generate more actionable insights on cellular and molecular events that explain the Bacillus-induced growth promotion and stress resilience in plants.

Synthetic bacterial community derived from a desert rhizosphere confers salt stress resilience to tomato in the presence of a soil microbiome

The root bacterial microbiome is important for the general health of the plant. Additionally, it can enhance tolerance to abiotic stresses, exemplified by plant species found in extreme ecological niches like deserts. These complex microbe-plant interactions can be simplified by constructing synthetic bacterial communities or SynComs from the root microbiome. Furthermore, SynComs can be applied as biocontrol agents to protect crops against abiotic stresses such as high salinity. However, there is little knowledge on the design of a SynCom that offers a consistent protection against salt stress for plants growing in a natural and, therefore, non-sterile soil which is more realistic to an agricultural setting. Here we show that a SynCom of five bacterial strains, originating from the root of the desert plant Indigofera argentea, protected tomato plants growing in a non-sterile substrate against a high salt stress. This phenotype correlated with the differential expression of salt stress related genes and ion accumulation in tomato. Quantification of the SynCom strains indicated a low penetrance into the natural soil used as the non-sterile substrate. Our results demonstrate how a desert microbiome could be engineered into a simplified SynCom that protected tomato plants growing in a natural soil against an abiotic stress.

A Review on the Role of Endophytes and Plant Growth Promoting Rhizobacteria in Mitigating Heat Stress in Plants

Among abiotic stresses, heat stress is described as one of the major limiting factors of crop growth worldwide, as high temperatures elicit a series of physiological, molecular, and biochemical cascade events that ultimately result in reduced crop yield. There is growing interest among researchers in the use of beneficial microorganisms. Intricate and highly complex interactions between plants and microbes result in the alleviation of heat stress. Plant–microbe interactions are mediated by the production of phytohormones, siderophores, gene expression, osmolytes, and volatile compounds in plants. Their interaction improves antioxidant activity and accumulation of compatible osmolytes such as proline, glycine betaine, soluble sugar, and trehalose, and enriches the nutrient status of stressed plants. Therefore, this review aims to discuss the heat response of plants and to understand the mechanisms of microbe-mediated stress alleviation on a physio-molecular basis. This review indicates that microbes have a great potential to enhance the protection of plants from heat stress and enhance plant growth and yield. Owing to the metabolic diversity of microorganisms, they can be useful in mitigating heat stress in crop plants. In this regard, microorganisms do not present new threats to ecological systems. Overall, it is expected that continued research on microbe-mediated heat stress tolerance in plants will enable this technology to be used as an ecofriendly tool for sustainable agronomy.

Biopriming of Maize Seeds with a Novel Bacterial Strain SH-6 to Enhance Drought Tolerance in South Korea

Maize is the third most common cereal crop worldwide, after rice and wheat, and plays a vital role in preventing global hunger crises. Approximately 50% of global crop yields are reduced by drought stress. Bacteria as biostimulants for biopriming can improve yield and enhance sustainable food production. Further, seed biopriming stimulates plant defense mechanisms. In this study, we isolated bacteria from the rhizosphere of Artemisia plants from Pohang beach, Daegu, South Korea. Twenty-three isolates were isolated and screened for growth promoting potential. Among them, bacterial isolate SH-6 was selected based on maximum induced tolerance to polyethylene glycol-simulated drought. SH-6 showed ABA concentration = 1.06 ± 0.04 ng/mL, phosphate solubilizing index = 3.7, and sucrose concentration = 0.51 ± 0.13 mg/mL. The novel isolate SH-6 markedly enhanced maize seedling tolerance to oxidative stress owing to the presence of superoxide dismutase, catalase, and ascorbate peroxidase activities in the culture media. Additionally, we quantified and standardized the biopriming effect of SH-6 on maize seeds. SH-6 significantly increased maize seedling drought tolerance by up to 20%, resulting in 80% germination potential. We concluded that the novel bacterium isolate SH-6 (gene accession number (OM757882) is a biostimulant that can improve germination performance under drought stress.

Effect of Trichoderma asperellum on Wheat Plants' Biochemical and Molecular Responses, and Yield under Different Water Stress Conditions

Eight Trichoderma strains were evaluated for their potential to protect wheat seedlings against severe (no irrigation within two weeks) water stress (WS). Considering the plant fresh weight and phenotype, T. asperellum T140, which displays 1-aminocyclopropane-1-carboxylic acid deaminase activity and which is able to produce several phytohormones, was selected. The molecular and biochemical results obtained from 4-week-old wheat seedlings linked T140 application with a downregulation in the WS-response genes, a decrease in antioxidant activities, and a drop in the proline content, as well as low levels of hydrogen peroxide and malondialdehyde in response to severe WS. All of these responses are indicative of T140-primed seedlings having a higher tolerance to drought than those that are left untreated. A greenhouse assay performed under high nitrogen fertilization served to explore the long-term effects of T140 on wheat plants subjected to moderate (halved irrigation) WS. Even though all of the plants showed acclimation to moderate WS regardless of T140 application, there was a positive effect exerted by T. asperellum on the level of tolerance of the wheat plants to this stress. Strain T140 modulated the expression of a plant ABA-dependent WS marker and produced increased plant superoxide dismutase activity, which would explain the positive effect of Trichoderma on increasing crop yields under moderate WS conditions. The results demonstrate the effectiveness of T. asperellum T140 as a biostimulant for wheat plants under WS conditions, making them more tolerant to drought.