Biofertilizers: An ecofriendly technology for nutrient recycling and environmental sustainability

Unveiling wheat growth promotion potential of phosphate solubilizing Pantoea agglomerans PS1 and PS2 through genomic, physiological, and metagenomic characterizations

Introduction

Phosphorus is an abundant element in the earth's crust and is generally found as complex insoluble conjugates. Plants cannot assimilate insoluble phosphorus and require external supplementation as chemical fertilizers to achieve a good yield. Continuous use of fertilizers has impacted soil ecology, and a sustainable solution is needed to meet plant elemental requirements. Phosphate solubilizing microbes could enhance phosphorus bioavailability for better crop production and can be employed to attain sustainable agriculture practices.

Methods

The current study unveils the biofertilizer potential of wheat rhizospheric bacteria through physiological, taxonomic, genomic, and microbiomics experimentations.

Results and Discussion

Culture-dependent exploration identified phosphate-solubilizing PS1 and PS2 strains from the wheat rhizosphere. These isolates were rod-shaped, gram-negative, facultative anaerobic bacteria, having optimum growth at 37°C and pH 7. Phylogenetic and phylogenomic characterization revealed their taxonomic affiliation as Pantoea agglomerans subspecies PS1 & PS2. Both isolates exhibited good tolerance against saline (>10% NaCl (w/v), >11.0% KCl (w/v), and >6.0% LiCl (w/v)), oxidizing (>5.9% H2O2 (v/v)) conditions. PS1 and PS2 genomes harbor gene clusters for biofertilization features, root colonization, and stress tolerance. PS1 and PS2 showed nitrate reduction, phosphate solubilization, auxin production, and carbohydrate utilization properties. Treatment of seeds with PS1 and PS2 significantly enhanced seed germination percentage (p = 0.028 and p = 0.008, respectively), number of tillers (p = 0.0018), number of leaves (p = 0.0001), number of spikes (p = 0.0001) and grain production (p = 0.0001). Wheat rhizosphere microbiota characterizations indicated stable colonization of PS1 and PS2 strains in treated seeds at different feek stages. Pretreatment of seeds with both strains engineered the wheat rhizosphere microbiota by recruiting plant growth-promoting microbial groups. In vitro, In vivo, and microbiota characterization studies indicated the biofertilizer potential of Pantoea sp. PS1 & PS2 to enhance wheat crop production. The employment of these strains could fulfill plant nutrient requirements and be a substitute for chemical fertilizers for sustainable agriculture.

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.

Assessing the effectiveness of indigenous phosphate-solubilizing bacteria in mitigating phosphorus fixation in acid soils

Phosphorus (P) is the key to several structural molecules and catalyzes numerous biochemical reactions in plant body besides its involvement in energy transfer. Any deficit in P availability is likely to result in reduced RNA and protein content, inhibiting crop growth and development. Thus, availability of soil P is extremely crucial for plant growth especially in acid soils of India, where most of the fraction is bound to solid phase rendering their availability. The present communication deals with the isolation of elite phosphate-solubilizing bacterial (PSB) strains from the acid soils to work out their ability to improve the fertilizer P use efficiency in the acidic environment. Initially twenty-six bacteria were isolated from the acid soils of Northeastern India. Among them, ten bacteria were selected based on formation of halo zone in the Pikovskaya agar plate. In addition, these bacteria were able to solubilize insoluble zinc (Zn) and potassium (K). The isolates were subject to in vitro optimization for P solubilization under different insoluble P source utilization and at different pH and salinity conditions. Strains AN3, AN11, and AN21 exhibited significant solubilization of insoluble P, Zn, and K, and were identified as Streptomyces sp., Enterobacter sp., and Paraburkholderia caribensis. These three bacteria solubilized 206.53 to 254.08 µg mL-1 P, 79.7 to 177.55 µg mL-1 Zn, and 0.96 to 1.56 µg mL-1 K from insoluble minerals. Their performance was further evaluated in pot culture experiment using green gram as test crop. These three bacteria were found to improve P uptake and dry matter accumulation in green gram plant substantially. Seed bio-priming with the PSB strains enhanced the efficiency of added P fertilizer, resulting in a 1.40 to 1.52 times higher effectiveness compared to the control. On the whole, AN11 may be ranked as best inoculant for the acidic soils of Northeastern India.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-024-04042-2.

The reduction of abiotic stress in food crops through climate-smart mycorrhiza-enriched biofertilizer

Climate change enhances stress in food crops. Recently, abiotic stress such as metalloid toxicity, salinity, and drought have increased in food crops. Mycorrhizal fungi can accumulate several nutrients within their hyphae through a symbiotic relationship and release them to cells in the root of the food crops under stress conditions. We have studied arbuscular mycorrhizal fungi (AMF)-enriched biofertilizers as a climate-smart technology option to increase safe and healthy food production under abiotic stress. AMF such as Glomus sp., Rhizophagus sp., Acaulospora morrowiae, Paraglomus occultum, Funneliformis mosseae, and Claroideoglomus etunicatum enhance growth and yield in food crops grown in soils under abiotic stress. AMF also works as a bioremediation material in food crops grown in soil. More precisely, the arsenic concentrations in grains decrease by 57% with AMF application. In addition, AMF increases mineral contents, and antioxidant activities under drought and salinity stress in food crops. Catalase (CAT) and ascorbate peroxidase (APX) increased by 45% and 70% in AMF-treated plants under drought stress. AMF-enriched biofertilizers are used in crop fields like precision agriculture to reduce the demand for chemical fertilizers. Subsequently, AMF-enriched climate-smart biofertilizers increase nutritional quality by reducing abiotic stress in food crops grown in soils. Consequently, a climate resilience environment might be developed using AMF-enriched biofertilizers for sustainable livelihood.

Impact of Agricultural Activities on Climate Change: A Review of Greenhouse Gas Emission Patterns in Field Crop Systems

This review paper synthesizes the current understanding of greenhouse gas (GHG) emissions from field cropping systems. It examines the key factors influencing GHG emissions, including crop type, management practices, and soil conditions. The review highlights the variability in GHG emissions across different cropping systems. Conventional tillage systems generally emit higher levels of carbon dioxide (CO2) and nitrous oxide (N2O) than no-till or reduced tillage systems. Crop rotation, cover cropping, and residue management can significantly reduce GHG emissions by improving soil carbon sequestration and reducing nitrogen fertilizer requirements. The paper also discusses the challenges and opportunities for mitigating GHG emissions in field cropping systems. Precision agriculture techniques, such as variable rate application of fertilizers and water, can optimize crop production while minimizing environmental impacts. Agroforestry systems, which integrate trees and crops, offer the potential for carbon sequestration and reducing N2O emissions. This review provides insights into the latest research on GHG emissions from field cropping systems and identifies areas for further study. It emphasizes the importance of adopting sustainable management practices to reduce GHG emissions and enhance the environmental sustainability of agricultural systems.

Differences in the constituents of bacterial microbiota of soils collected from two fields of diverse potato blackleg and soft rot diseases incidences, a case study

The presence of bacteria from the Dickeya spp. and Pectobacterium spp. in farmlands leads to global crop losses of over $420 million annually. Since 1982, the scientists have started to suspect that the development of disease symptoms in crops might be inhibited by bacteria present in the soil. Here, we characterized in terms of physicochemical properties and the composition of bacterial soil microbiota two fields differing, on the basis of long-term studies, in the occurrence of Dickeya spp.- and Pectobacterium spp.-triggered infections. Majority, i.e. 17 of the investigated physicochemical features of the soils collected from two fields of either low or high potato blackleg and soft rot diseases incidences turned out to be similar, in contrast to the observed 4 deviations in relation to Mg, Mn, organic C and organic substance contents. By performing microbial cultures and molecular diagnostics-based identification, 20 Pectobacterium spp. strains were acquired from the field showing high blackleg and soft rot incidences. In addition, 16S rRNA gene amplicon sequencing followed by bioinformatic analysis revealed differences at various taxonomic levels in the soil bacterial microbiota of the studied fields. We observed that bacteria from the genera Bacillus, Rumeliibacillus, Acidobacterium and Gaiella turned out to be more abundant in the soil samples originating from the field of low comparing to high frequency of pectinolytic bacterial infections. In the herein presented case study, it is shown for the first time that the composition of bacterial soil microbiota varies between two fields differing in the incidences of soft rot and blackleg infections.

Biopreparations for the decomposition of crop residues

Recently, there has been growing interest in biopreparations that intensify the decomposition of crop residues. These preparations can promote nutrient cycling and soil fertility, ultimately supporting healthy plant growth and increasing agricultural productivity. However, the development and commercialization of biopreparations poses unique challenges. Producers of biopreparations struggle to develop highly effective preparations, which then face regulatory hurdles and must win market acceptance. This literature review provides up-to-date data on microbial preparations available commercially on the European market, along with information on current relevant regulations. Challenges for the development and commercialization of new biopreparations are also discussed. The development and commercialization of biopreparations require a comprehensive approach that addresses the complex interplay of microbial and environmental factors. The need for more specific regulations on biopreparations for decomposing crop residues, clearer instructions on their use, and further research on the overall impact of biopreparations on the soil metabolome and optimal conditions for their application were indicated. Moreover, manufacturers should prioritize the development of high-quality products that meet the needs of farmers and address concerns about environmental impact and public acceptance.

Humic acid and grafting as sustainable agronomic practices for increased growth and secondary metabolism in cucumber subjected to salt stress

Salinity stress poses a significant treat to crop yields and product quality worldwide. Application of a humic acid bio stimulant and grafting onto tolerant rootstocks can both be considered sustainable agronomic practices that can effectively ameliorate the negative effects of salinity stress. This study aimed to assess the above mentioned ameliorative effects of both practices on cucumber plants subjected to saline environments. To attain this goal a factorial experiment was carried out in the form of a completely randomized design with three replications. The three factors considered were (a) three different salinity levels (0, 5, and 10 dS m-1 of NaCl), (b) foliar application of humic acid at three levels (0, 100, and 200 mg L-1), and (c) both grafted and ungrafted plants. Vegetative traits including plant height, fresh and dry weight and number of leaf exhibited a significant decrease under increasing salinity stress. However, the application of humic acid at both levels mitigated these effects compared to control plants. The reduction in relative water content (RWC) of the leaf caused by salinity, was compensated by the application of humic acid and grafting. Thus, the highest RWC (86.65%) was observed in grafting plants with 0 dS m-1 of NaCl and 20 mg L-1 of humic acid. Electrolyte leakage (EL) increased under salinity stress, but the application of humic acid and grafting improved this trait and the lowest amount of EL (26.95%) was in grafting plants with 0 dS m-1 of NaCl and 20 mg L-1 of humic acid. The highest amount of catalase (0.53 mmol H2O2 g-1 fw min-1) and peroxidase (12.290 mmol H2O2 g-1 fw min-1) enzymes were observed in the treatment of 10 dS m-1 of NaCl and 200 mg L-1 humic acid. The highest amount of total phenol (1.99 mg g-1 FW), total flavonoid (0.486 mg g-1 FW), total soluble carbohydrate (30.80 mg g-1 FW), soluble protein (34.56 mg g-1 FW), proline (3.86 µg g-1 FW) was in grafting plants with 0 dS m-1 of NaCl and 200 mg L-1 of humic acid. Phenolic acids and phenylalanine ammonia lyase (PAL) and polyphenol oxidase (PPO) enzymes increased with increasing salinity and humic acid levels. Contrary to humic acid, salt stress increased the sodium (Na+) and chlorine (Cl-) and decreased the amount of potassium (K+) and calcium (Ca2+) in the root and leaf of ungrafted cucumber. However, the application 200 mg L-1 humic acid appeared to mitigate these effects, thereby suggesting a potential role in moderating physiological processes and improving growth of cucumber plants subjected to salinity stress. According to the obtained results, spraying of humic acid (200 mg L-1) and the use of salt resistant rootstocks are recommended to increase tolerance to salt stress in cucumber. These results, for the first time, clearly demonstrated that fig leaf gourd a new highly salt-tolerant rootstock, enhances salt tolerance and improves yield and quality of grafted cucumber plants by reducing sodium transport to the shoot and increasing the amount of compatible osmolytes.

Polycyclic aromatic hydrocarbon: underpinning the contribution of specialist microbial species to contaminant mitigation in the soil

The persistence of PAHs poses a significant challenge for conventional remediation approaches, necessitating the exploration of alternative, sustainable strategies for their mitigation. This review underscores the vital role of specialized microbial species (nitrogen-fixing, phosphate-solubilizing, and biosurfactant-producing bacteria) in tackling the environmental impact of polycyclic aromatic hydrocarbons (PAHs). These resistant compounds demand innovative remediation strategies. The study explores microbial metabolic capabilities for converting complex PAHs into less harmful byproducts, ensuring sustainable mitigation. Synthesizing literature from 2016 to 2023, it covers PAH characteristics, sources, and associated risks. Degradation mechanisms by bacteria and fungi, key species, and enzymatic processes are examined. Nitrogen-fixing and phosphate-solubilizing bacteria contributions in symbiotic relationships with plants are highlighted. Biosurfactant-producing bacteria enhance PAH solubility, expanding microbial accessibility for degradation. Cutting-edge trends in omics technologies, synthetic biology, genetic engineering, and nano-remediation offer promising avenues. Recommendations emphasize genetic regulation, field-scale studies, sustainability assessments, interdisciplinary collaboration, and knowledge dissemination. These insights pave the way for innovative, sustainable PAH-contaminated environment restoration.

Comparative genomics reveals insights into the potential of Lysinibacillus irui as a plant growth promoter

Members of the genus Lysinibacillus attract attention for their mosquitocidal, bioremediation, and plant growth-promoting abilities. Despite this interest, comprehensive studies focusing on genomic traits governing plant growth and stress resilience in this genus using whole-genome sequencing are still scarce. Therefore, we sequenced and compared the genomes of three endophytic Lysinibacillus irui strains isolated from Canary Island date palms with the ex-type strain IRB4-01. Overall, the genomes of these strains consist of a circular chromosome with an average size of 4.6 Mb and a GC content of 37.2%. Comparative analysis identified conserved gene clusters within the core genome involved in iron acquisition, phosphate solubilization, indole-3-acetic acid biosynthesis, and volatile compounds. In addition, genome analysis revealed the presence of genes encoding carbohydrate-active enzymes, and proteins that confer resistance to oxidative, osmotic, and salinity stresses. Furthermore, pathways of putative novel bacteriocins were identified in all genomes. This illustrates possible common plant growth-promoting traits shared among all strains of L. irui. Our findings highlight a rich repertoire of genes associated with plant lifestyles, suggesting significant potential for developing inoculants to enhance plant growth and resilience. This study is the first to provide insights into the overall genomic signatures and mechanisms of plant growth promotion and biocontrol in the genus Lysinibacillus. KEY POINTS: • Pioneer study in elucidating plant growth promoting in L. irui through comparative genomics. • Genome mining identified biosynthetic pathways of putative novel bacteriocins. • Future research directions to develop L. irui-based biofertilizers for sustainable agriculture.

Regulatory mechanisms of plant rhizobacteria on plants to the adaptation of adverse agroclimatic variables

The mutualistic plant rhizobacteria which improve plant development and productivity are known as plant growth-promoting rhizobacteria (PGPR). It is more significant due to their ability to help the plants in different ways. The main physiological responses, such as malondialdehyde, membrane stability index, relative leaf water content, photosynthetic leaf gas exchange, chlorophyll fluorescence efficiency of photosystem-II, and photosynthetic pigments are observed in plants during unfavorable environmental conditions. Plant rhizobacteria are one of the more crucial chemical messengers that mediate plant development in response to stressed conditions. The interaction of plant rhizobacteria with essential plant nutrition can enhance the agricultural sustainability of various plant genotypes or cultivars. Rhizobacterial inoculated plants induce biochemical variations resulting in increased stress resistance efficiency, defined as induced systemic resistance. Omic strategies revealed plant rhizobacteria inoculation caused the upregulation of stress-responsive genes-numerous recent approaches have been developed to protect plants from unfavorable environmental threats. The plant microbes and compounds they secrete constitute valuable biostimulants and play significant roles in regulating plant stress mechanisms. The present review summarized the recent developments in the functional characteristics and action mechanisms of plant rhizobacteria in sustaining the development and production of plants under unfavorable environmental conditions, with special attention on plant rhizobacteria-mediated physiological and molecular responses associated with stress-induced responses.

IAA-producing plant growth promoting rhizobacteria from Ceanothus velutinus enhance cutting propagation efficiency and Arabidopsis biomass

Climate-induced drought impacts plant growth and development. Recurring droughts increase the demand for water for food production and landscaping. Native plants in the Intermountain West region of the US are of keen interest in low water use landscaping as they are acclimatized to dry and cold environments. These native plants do very well at their native locations but are difficult to propagate in landscape. One of the possible reasons is the lack of associated microbiome in the landscaping. Microbiome in the soil contributes to soil health and impacts plant growth and development. Here, we used the bulk soil from the native plant Ceanothus velutinus (snowbrush ceanothus) as inoculant to enhance its propagation. Snowbrush ceanothus is an ornamental plant for low-water landscaping that is hard to propagate asexually. Using 50% native bulk soil as inoculant in the potting mix significantly improved the survival rate of the cuttings compared to no-treated cuttings. Twenty-four plant growth-promoting rhizobacteria (PGPR) producing indole acetic acid (IAA) were isolated from the rhizosphere and roots of the survived snowbrush. Seventeen isolates had more than 10µg/mL of IAA were shortlisted and tested for seven different plant growth-promoting (PGP) traits; 76% showed nitrogen-fixing ability on Norris Glucose Nitrogen free media,70% showed phosphate solubilization activity, 76% showed siderophore production, 36% showed protease activity, 94% showed ACC deaminase activity on DF-ACC media, 76% produced catalase and all of isolates produced ammonia. Eight of seventeen isolates, CK-6, CK-22, CK-41, CK-44, CK-47, CK-50, CK-53, and CK-55, showed an increase in shoot biomass in Arabidopsis thaliana. Seven out of eight isolates were identified as Pseudomonas, except CK-55, identified as Sphingobium based on 16S rRNA gene sequencing. The shortlisted isolates are being tested on different grain and vegetable crops to mitigate drought stress and promote plant growth.

Pseudomonas putida configures Arabidopsis root architecture through modulating the sensing systems for phosphate and iron acquisition

Iron (Fe) and phosphate (Pi) are two essential nutrients that are poorly available in the soil and should be supplemented either as fertilizers or organic amendments to sustain crop production. Currently, determining how rhizosphere bacteria contribute to plant mineral nutrient acquisition is an area of growing interest regarding its potential application in agriculture. The aim of this study was to investigate the influence of root colonization by Pseudomonas putida for Arabidopsis growth through Fe and Pi nutritional signaling. We found that root colonization by the bacterium inhibits primary root elongation and promotes the formation of lateral roots. These effects could be related to higher expression of two Pi starvation-induced genes and AtPT1, the major Pi transporter in root tips. In addition, P. putida influenced the accumulation of Fe in the root and the expression of different elements of the Fe uptake pathway. The loss of function of the protein ligase BRUTUS (BTS), and the bHLH transcription factors POPEYE (PYE) and IAA-LEUCINE RESISTANT3 (ILR3) compromised the root branching stimulation triggered by bacterial inoculation while the leaf chlorosis in the fit1 and irt1-1 mutant plants grown under standard conditions could be bypassed by P. putida inoculation. The WT and both mutant lines showed similar Fe accumulation in roots. P. putida repressed the expression of the IRON-REGULATED TRANSPORTER 1 (IRT1) gene suggesting that the bacterium promotes an alternative Fe uptake mechanism. These results open the door for the use of P. putida to enhance nutrient uptake and optimize fertilizer usage by plants.

Role of calcium nutrition in plant Physiology: Advances in research and insights into acidic soil conditions - A comprehensive review

Plant mineral nutrition has immense significance for crop productivity and human well-being. Soil acidity plays a major role in determining the nutrient availability that influences plant growth. The importance of calcium (Ca) in biological processes, such as signaling, metabolism, and cell growth, underlines its critical role in plant growth and development. This review focuses on soil acidification, a gradual process resulting from cation leaching, fertilizer utilization, and drainage issues. Soil acidification significantly hampers global crop production by modifying nutrient accessibility. In acidic soils, essential nutrients, such as nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), and Ca become less accessible, establishing a correlation between soil pH and plant nutrition. Cutting-edge Ca nutrition technologies, including nanotechnology, genetic engineering, and genome sequencing, offer the potential to deliver Ca and reduce the reliance on conventional soluble fertilizers. These fertilizers not only contribute to environmental contamination but also impose economic burdens on farmers. Nanotechnology can enhance nutrient uptake, and Ca nanoparticles improve nutrient absorption and release. Genetic engineering enables the cultivation of acid-tolerant crop varieties by manipulating Ca-related genes. High-throughput technologies such as next-generation sequencing and microarrays aid in identifying the microbial structures, functions, and biosynthetic pathways involved in managing plant nutritional stress. The ultimate goal is to shed light on the importance of Ca, problems associated with soil acidity, and potential of emerging technologies to enhance crop production while minimizing the environmental impact and economic burden on farmers.

Nodulation Experiment by Cross-Inoculation of Nitrogen-Fixing Bacteria Isolated from Root Nodules of Several Leguminous Plants

Root-nodule nitrogen-fixing bacteria are known for being specific to particular legumes. This study isolated the endophytic root-nodule bacteria from the nodules of legumes and examined them to determine whether they could be used to promote the formation of nodules in other legumes. Forty-six isolates were collected from five leguminous plants and screened for housekeeping (16S rRNA), nitrogen fixation (nifH), and nodulation (nodC) genes. Based on the 16S rRNA gene sequencing and phylogenetic analysis, the bacterial isolates WC15, WC16, WC24, and GM5 were identified as Rhizobium, Sphingomonas, Methylobacterium, and Bradyrhizobium, respectively. The four isolates were found to have the nifH gene, and the study confirmed that one isolate (GM5) had both the nifH and nodC genes. The Salkowski method was used to measure the isolated bacteria for their capacity to produce phytohormone indole acetic acid (IAA). Additional experiments were performed to examine the effect of the isolated bacteria on root morphology and nodulation. Among the four tested isolates, both WC24 and GM5 induced nodulation in Glycine max. The gene expression studies revealed that GM5 had a higher expression of the nifH gene. The existence and expression of the nitrogen-fixing genes implied that the tested strain had the ability to fix the atmospheric nitrogen. These findings demonstrated that a nitrogen-fixing bacterium, Methylobacterium (WC24), isolated from a Trifolium repens, induced the formation of root nodules in non-host leguminous plants (Glycine max). This suggested the potential application of these rhizobia as biofertilizer. Further studies are required to verify the N2-fixing efficiency of the isolates.

Colonization of root endophytic fungus Serendipita indica improves drought tolerance of Pinus taeda seedlings by regulating metabolome and proteome

Pinus taeda is an important forest tree species for plantations because of its rapid growth and high yield of oleoresins. Although P. taeda plantations distribute in warm and wet southern China, drought, sometime serious and long time, often occurs in the region. To explore drought tolerance of P. taeda and usage of beneficial microorganisms, P. taeda seedlings were planted in pots and were inoculated with root endophytic fungus Serendipita indica and finally were treated with drought stress for 53 d. Metabolome and proteome of their needles were analyzed. The results showed that S. indica inoculation of P. taeda seedlings under drought stress caused great changes in levels of some metabolites in their needles, especially some flavonoids and organic acids. Among them, the levels of eriocitrin, trans-aconitic acid, vitamin C, uric acid, alpha-ketoglutaric acid, vitamin A, stachydrine, coumalic acid, itaconic acid, calceolarioside B, 2-oxoglutaric acid, and citric acid were upregulated more than three times in inoculated seedlings under drought stress, compared to those of non-inoculated seedlings under drought stress. KEGG analysis showed that some pathways were enriched in inoculated seedlings under drought stress, such as flavonoid biosynthesis, ascorbate and aldarate metabolism, C5-branched dibasic acid metabolism. Proteome analysis revealed some specific differential proteins. Two proteins, namely, H9X056 and H9VDW5, only appeared in the needles of inoculated seedlings under drought stress. The protein H9VNE7 was upregulated more than 11.0 times as that of non-inoculated seedlings under drought stress. In addition, S. indica inoculation increased enrichment of water deficient-inducible proteins (such as LP3-1, LP3-2, LP3-3, and dehydrins) and those involved in ribosomal structures (such as A0A385JF23). Meanwhile, under drought stress, the inoculation caused great changes in biosynthesis and metabolism pathways, mainly including phenylpropanoid biosynthesis, cutin, suberine and wax biosynthesis, and 2-oxocarboxylic acid metabolism. In addition, there were positive relationships between accumulation of some metabolites and enrichment of proteins in P. taeda under drought stress. Altogether, our results showed great changes in metabolome and proteome in inoculated seedlings under drought stress and provided a guideline to further study functions of metabolites and proteins, especially those related to drought stress.

A review of chitosan nanoparticles: Nature's gift for transforming agriculture through smart and effective delivery mechanisms

Chitosan nanoparticles (CNPs) have emerged as a promising tool in agricultural advancements due to their unique properties including, biocompatability, biodegradability, non-toxicity and remarkable versatility. These inherent properties along with their antimicrobial, antioxidant and eliciting activities enable CNPs to play an important role in increasing agricultural productivity, enhancing nutrient absorption and improving pest management strategies. Furthermore, the nano-formulation of chitosan have the ability to encapsulate various agricultural amendments, enabling the controlled release of pesticides, fertilizers, plant growth promoters and biocontrol agents, thus offering precise and targeted delivery mechanisms for enhanced efficiency. This review provides a comprehensive analysis of the latest research and developments in the use of CNPs for enhancing agricultural practices through smart and effective delivery mechanisms. It discusses the synthesis methods, physicochemical properties, and their role in enhancing seed germination and plant growth, crop protection against biotic and abiotic stresses, improving soil quality and reducing the environmental pollution and delivery of agricultural amendments. Furthermore, the potential environmental benefits and future directions for integrating CNPs into sustainable agricultural systems are explored. This review aims to shed light on the transformative potential of chitosan nanoparticles as nature's gift for revolutionizing agriculture and fostering eco-friendly farming practices.

Parameter evaluation for developing phosphate-solubilizing Bacillus inoculants

Bacterial inoculants have been used in agriculture to improve plant performance. However, laboratory and field requirements must be completed before a candidate can be employed as an inoculant. Therefore, this study aimed to evaluate the parameters for inoculant formulation and the potential of Bacillus subtilis (B70) and B. pumilus (B32) to improve phosphorus availability in maize (Zea mays L.) crops. In vitro experiments assessed the bacterial ability to solubilize and mineralize phosphate, their adherence to roots, and shelf life in cassava starch (CS), carboxymethyl cellulose (CMC), peat, and activated charcoal (AC) stored at 4 °C and room temperature for 6 months. A field experiment evaluated the effectiveness of strains to increase the P availability to plants growing with rock phosphate (RP) and a mixture of RP and triple superphosphate (TS) and their contribution to improving maize yield and P accumulation in grains. The B70 was outstanding in solubilizing RP and phytate mineralization and more stable in carriers and storage conditions than B32. However, root adherence was more noticeable in B32. Among carriers, AC was the most effective for preserving viable cell counts, closely similar to those of the initial inoculum of both strains. Maize productivity using the mixture RPTS was similar for B70 and B32. The best combination was B70 with RP, which improved the maize yield (6532 kg ha-1) and P accumulation in grains (15.95 kg ha-1). Our results indicated that the inoculant formulation with AC carrier and B70 is a feasible strategy for improving phosphorus mobilization in the soil and maize productivity.

Ciceribacter sichuanensis sp. nov., a plant growth promoting rhizobacterium isolated from root nodules of soybean in Sichuan, China

The fast-growing rhizobia-like strains S101T and S153, isolated from root nodules of soybean (Glycine max) in Sichuan, People's Republic of China, underwent characterization using a polyphasic taxonomy approach. The strains exhibited growth at 20-40 °C (optimum, 28 °C), pH 4.0-10.0 (optimum, pH 7.0) and up to 2.0% (w/v) NaCl (optimum, 0.01%) on Yeast Mannitol Agar plates. The 16S rRNA gene of strain S101T showed 98.4% sequence similarity to the closest type strain, Ciceribacter daejeonense L61T. Major cellular fatty acids in strain S101T included summed feature 8 (C18:1ω7c and/or C18:1ω6c) and C19:0 cyclo ω8c. The predominant quinone was ubiquinone-10. The polar lipids of strain S101T included diphosphatidylglycerol, phosphatidylglycerol, phosphatidylmethyl ethanolamine, phosphatidyl ethanolamine, amino phospholipid, unidentified phosphoglycolipid and unidentified amino-containing lipids. The DNA G + C contents of S101T and S153 were 61.1 and 61.3 mol%, respectively. Digital DNA-DNA hybridization relatedness and average nucleotide identity values between S101T and C. daejeonense L61T were 46.2% and 91.4-92.2%, respectively. In addition, strain S101T promoted the growth of soybean and carried nitrogen fixation genes in its genome, hinting at potential applications in sustainable agriculture. We propose that strains S101T and S153 represent a novel species, named Ciceribacter sichuanensis sp. nov., with strain S101T as the type strain (= CGMCC 1.61309 T = JCM 35649 T).

Bacillus species as tools for biocontrol of plant diseases: A meta-analysis of twenty-two years of research, 2000-2021

The traditional way of dealing with plant diseases has been the use of chemical products, but these harm the environment and are incompatible with the global effort for sustainable development. The use of Bacillus and related species in the biological control of plant diseases is a trend in green agriculture. Many studies report the positive effect of these bacteria, but a synthesis is still necessary. So, the objective of this work is to perform a meta-analysis of Bacillus biocontrol potential and identify factors that drive its efficacy. Data were compiled from articles published in journals listed in two of the main scientific databases between 2000 and 2021. Among 6159 articles retrieved, 399 research papers met the inclusion criteria for a systematic review. Overall, Bacilli biocontrol agents reduced disease by 60% compared to control groups. Furthermore, experimental tests with higher concentrations show a strong protective effect, unlike low and single concentration essays. Biocontrol efficacy also increased when used as a protective inoculation rather than therapeutic inoculation. Inoculation directly in the fruit has a greater effect than soil drenching. The size of the effect of Bacillus-based commercial products is lower than the newly tested strains. The findings presented in this study confirm the power of Bacillus-based bioinoculants and provide valuable guidance for practitioners, researchers, and policymakers seeking effective and sustainable solutions in plant disease management.

Microalgae biomass as a conditioner and regulator of soil quality and fertility

Characteristics of an acid soil cultivated with Urochloa brizantha cv. Marandu were evaluated in relation to two types of fertilization: a conventional one, chemical based on nitrogen and potassium, and a biofertilizer, based on microalgae biomass. The results were compared among three treatments, control, conventional, and biological fertilization, with seven replications each. The study evaluated microalgae community, total carbon and nitrogen contents, mineral nitrogen, and enzymatic activity. Chlorella vulgaris showed the highest organism density, which can be explained by its rapid growth and high resistance. The highest species diversity was detected in the control 1,380,938 org cm-3 and biological 1,841,250 org cm-3 treatments, with the latter showing a higher density of cyanobacteria, especially Pseudanabaena limnetica with 394,554 org cm-3. The soil treated with chemical fertilization showed higher nitrate (9.14 mg NKg-1 NO3--N) and potassium (52.32 mg dm-3) contents. The highest levels of sulfur (21.73 mg dm-3) and iron (96.46 mgdm-3) were detected in the biological treatment. The chemical treatment showed higher activity of the enzymes acid phosphatase, acetylglucosaminidase, and sulfatase, while α-glucosidase and leucine aminopeptidase stood out in the biological treatment. Soil properties were not significantly affected by the treatments. The use of microalgae biomass derived from wastewater treatment from milking parlors was evaluated and presented as a promising biofertilizer for agriculture, following the line of recovering nutrient-rich wastes. In this sense, although many challenges need to be overcome, the results suggest that microalgal-based fertilizers could lead to low-impact agriculture.

Effect of a native bacterial consortium on growth, yield, and grain quality of durum wheat (Triticum turgidum L. subsp. durum) under different nitrogen rates in the Yaqui Valley, Mexico

A field experiment was carried out to quantify the effect of a native bacterial inoculant on the growth, yield, and quality of the wheat crop, under different nitrogen (N) fertilizer rates in two agricultural seasons. Wheat was sown under field conditions at the Experimental Technology Transfer Center (CETT-910), as a representative wheat crop area from the Yaqui Valley, Sonora México. The experiment was conducted using different doses of nitrogen (0, 130, and 250 kg N ha-1) and a bacterial consortium (BC) (Bacillus subtilis TSO9, B. cabrialesii subsp. tritici TSO2T, B. subtilis TSO22, B. paralicheniformis TRQ65, and Priestia megaterium TRQ8). Results showed that the agricultural season affected chlorophyll content, spike size, grains per spike, protein content, and whole meal yellowness. The highest chlorophyll and Normalized Difference Vegetation Index (NDVI) values, as well as lower canopy temperature values, were observed in treatments under the application of 130 and 250 kg N ha-1 (the conventional Nitrogen dose). Wheat quality parameters such as yellow berry, protein content, Sodium dodecyl sulfate (SDS)-Sedimentation, and whole meal yellowness were affected by the N dose. Moreover, the application of the native bacterial consortium, under 130 kg N ha-1, resulted in a higher spike length and grain number per spike, which led to a higher yield (+1.0 ton ha-1 vs. un-inoculated treatment), without compromising the quality of grains. In conclusion, the use of this bacterial consortium has the potential to significantly enhance wheat growth, yield, and quality while reducing the nitrogen fertilizer application, thereby offering a promising agro-biotechnological alternative for improving wheat production.

Improved plant yield of potato through exogenously applied potassium fertilizer sources and biofertilizer

Excessive usage of chemical fertilizers has detrimental effects on the environment and the safety of food. Conversely, utilizing organic fertilizers such as sage offers several advantages, including cost-effectiveness, soil enhancement, and promotion of root development. A two-year field experiment was conducted to investigate the impact of different potassium fertilizer sources and biofertilizers (specifically Bacillus cereus (MBc)) on potato plants. The experiment employed a split-plot design with three replicates, where the main plot factor was MBc (with and without), and the subplot factor was the sources of potassium fertilizer (control without K fertilizer, 100% Feldspar (FD), 100% Filter cake (FC), 75% FD + 25% FC, 25% FD + 75% FC, and 50% FD + 50% FC). The purpose was to examine the growth response of potato plants to these treatments. The results indicated that all treatments increased plant height, stem count, and tuber dry matter compared to the control. Furthermore, all treatments exhibited a higher uptake of macronutrients (N, P, and K) compared to the control. Notably, the plants treated with 100FC combined with MBc showed a significant 104.74% increase in total tuber weight compared to the control treatment. Additionally, the addition of 100FC with MBc significantly enhanced the availability of N, P, and K by 73.13%, 110.33%, and 51.88% respectively, compared to the control treatment. Apart from the biofertilizers, the individual application of FC and its combination with FD also demonstrated positive effects on soil fertility, potato growth, and yield.

Liquid Bioformulation: A Trending Approach Towards Achieving Sustainable Agriculture

The human population is expanding at an exponential rate, and has created a great surge in the demand for food production. To intensify the rate of crop production, there is a tremendous usage of chemical pesticides and fertilizers. The practice of using these chemicals to enhance crop productivity has resulted in the degradation of soil fertility, leading to the depletion of native soil microflora. The constant application of these hazardous chemicals in the soil possesses major threat to humans and animals thereby impacting the agroecosystem severely. Hence, it is very important to hunt for certain new alternatives for enhancing crop productivity in an eco-friendly manner by using the microbial bioformulations. Microbial bioformulations can be mainly divided into two types: solid and liquid. There is a lot of information available on the subject of solid bioformulation, but the concept of liquid bioformulation is largely ignored. This article focuses on the diverse spectrum of liquid bioformulation pertaining to the market capture, its different types, potency of the product, mode of usage, and the limitations encountered. Also the authors have tried to include all the strategies required for sensitizing and making liquid bioformulation approach cost effective and as a greener strategy to succeed in developing countries.

A comprehensive overview of eco-friendly bio-fertilizers extracted from living organisms

Currently, sustainable agriculture involves ecofriendly techniques, which include biofertilization. Biofertilizers increase plant productivity by improving soil fertility and nutrient content. A wide range of living organisms can be applied as biofertilizers and increase soil fertility without causing pollution due to their biodegradability. The organisms can be microorganisms like bacteria, microalgae, and micro fungi or macro organisms like macroalgae, macro fungi, and higher plants. Biofertilizers extracted from living organisms or their residues will be increasingly used rather than chemical fertilizers, which cause heavy metal accumulation in soil. Biofertilizer use aims for sustainable development in agriculture by maintaining the soil. This will mitigate climate change and related impacts and will also lower many serious diseases resulting from pollution such as cancer, liver and renal failure, and immune diseases. This review is a comprehensive overview of biofertilizers extracted from a range of living organisms from the Kingdoms Monera to Plantae and included bacteria, algae, fungi, and higher plants. Organisms that play a vital role in elevating soil nutrients in a safe, cheap, and ecofriendly manner are included in the review to promote their potential commercial application.

Impact of PGPR inoculation on root morphological traits and root exudation in rapeseed and camelina: interactions with heat stress

Root exudation is involved in the recruitment of beneficial microorganisms by trophic relationships and/or signalling pathways. Among beneficial microorganisms, Plant Growth-Promoting Rhizobacteria (PGPR) are known to improve plant growth and stress resistance. These interactions are of particular importance for species that do not interact with mycorrhizal fungi, such as rapeseed (Brassica napus L.) and camelina (Camelina sativa (L.) Crantz). However, heat stress is known to have a quantitative and qualitative impact on root exudation and could affect the interactions between plants and PGPR. We aimed to analyse the effects of PGPR inoculation on root morphology and exudation in rapeseed and camelina at the reproductive stage. The modulation of the effects of these interactions under heat stress was also investigated. The plants were inoculated twice at the reproductive stage with two different Pseudomonas species and were exposed to heat stress after the second inoculation. In non-stressing conditions, after bacterial inoculation, rapeseed and camelina exhibited two contrasting behaviours in C root allocation. While rapeseed plants seemed to suffer from the interactions with the bacteria, camelina plants appeared to control the relationship with the PGPR by modifying the composition of their root exudates. Under heat stress, the plant-PGPR interaction was unbalanced for rapeseed, for which the C allocation strategy is mainly driven by the C cost from the bacteria. Alternatively, camelina plants prioritized C allocation for their own above-ground development. This work opens up new perspectives for understanding plant-PGPR interactions, especially in an abiotic stress context.

Green economic revival acquisition: evaluating impact of digital finance and natural resource development

Digital financing is an emerging source after COVID-19 to address novel problems of economies and different industries. With the growing concern about the sustainability of the global environment, developing countries are now moving toward unprecedented economic development. This research analyzes the impact of digital finance and economic growth on environmental sustainability in China from 1995 to 2020, focusing on natural resource management. To include asymmetric patterns and handle socioeconomic shocks during the last three decades, the research uses the cutting-edge ordinary least square (O.L.S.) methodology. The O.L.S. helps the research findings and illustrated patterns of ecological sustainability dependency across various data distributions. According to the empirical results, N.R., F.D.P., and G.D.P. all benefited from carbon emissions at higher and lower emissions quantiles. Green technology innovation, on the other hand, considerably reduces emissions across all quantiles. Notably, the effect of each repressor significantly changed for lower, medium, and higher emissions quantiles, showing a thorough understanding of China's resource scarcity and sustainable growth.

Characterizing indigenous plant growth promoting bacteria and their synergistic effects with organic and chemical fertilizers on wheat (Triticum aestivum)

The excessive use of chemical fertilizers is deteriorating both the environment and soil, making it a big challenge faced by sustainable agriculture. To assist the efforts for the solution of this burning issue, nine different potential native strains of plant growth-promoting bacteria (PGPB) namely, SA-1(Bacillus subtilis), SA-5 (Stenotrophomonas humi),SA-7(Azospirillum brasilense), BH-1(Azospirillum oryzae), BH-7(Azotobacter armeniacus), BH-8(Rhizobium pusense), BA-3(Azospirillum zeae), BA-6(Rhizobium pusense), and BA-7(Pseudomonas fragi) were isolated that were characterized morphologically, biochemically and molecularly on the basis of 16S rRNA sequencing. Furthermore, the capability of indigenous PGPB in wheat (Triticum aestivum, Chakwal-50) under control, DAP+FYM, SA-1,5,7, BH-1,7,8, BA-3,6,7, DAP+ FYM + SA-1,5,7, DAP+FYM+ BH-1,7,8 and DAP+FYM+ BA-3,6,7 treatments was assessed in a randomized complete block design (RCBD). The results of the study showed that there was a significant increase in plant growth, nutrients, quality parameters, crop yield, and soil nutrients at three depths under SA-1,5,7, BH-1,7,8, and BA-3,6,7 in combination with DAP+FYM. Out of all these treatments, DAP+ FYM + BA-3,6,7 was found to be the most efficient for wheat growth having the highest 1000-grain weight of 55.1 g. The highest values for plant height, no. of grains/spike, spike length, shoot length, root length, shoot dry weight, root dry weight, 1000 grain weight, biological yield, and economic yield were found to be 90.7 cm, 87.7 cm, 7.20 cm, 53.5 cm, 33.5 cm, 4.87 g, 1.32 g, 55.1 g, 8209 kg/h, and 4572 kg/h, respectively, in the DAP+FYM+BA treatment. The DAP+FYM+BA treatment had the highest values of TN (1.68 µg/mL), P (0.38%), and K (1.33%). Likewise, the value of mean protein (10.5%), carbohydrate (75%), lipid (2.5%), and available P (4.68 ppm) was also highest in the DAP+FYM+BA combination. C:P was found to be significantly highest (20.7) in BA alone but was significantly lowest (11.9) in DAP+FYM+BA. Hence, the integration of strains BA-3, BA-5, and BA-7 in fertilizers can be regarded as the most suitable choice for agricultural growth in the sub-mountainous lower region of AJK. This could serve as the best choice for sustainable wheat growth and improved soil fertility with lesser impacts on the environment.

Enhance of tomato production and induction of changes on the organic profile mediated by Rhizobium biofortification

Introduction

The extensive use of chemical fertilizers has served as a response to the increasing need for crop production in recent decades. While it addresses the demand for food, it has resulted in a decline in crop productivity and a heightened negative environmental impact. In contrast, plant probiotic bacteria (PPB) offer a promising alternative to mitigate the negative consequences of chemical fertilizers. PPB can enhance nutrient availability, promote plant growth, and improve nutrient uptake efficiency, thereby reducing the reliance on chemical fertilizers.

Methods

This study aimed to evaluate the impact of native Rhizobium strains, specifically Rhizobium calliandrae LBP2-1, Rhizobium mayense NSJP1-1, and Rhizobium jaguaris SJP1- 2, on the growth, quality, and rhizobacterial community of tomato crops. Various mechanisms promoting plant growth were investigated, including phosphate solubilization, siderophore production, indole acetic acid synthesis, and cellulose and cellulase production. Additionally, the study involved the assessment of biofilm formation and root colonization by GFP-tagged strains, conducted a microcosm experiment, and analyzed the microbial community using metagenomics of rhizospheric soil.

Results

The results showed that the rhizobial strains LBP2-1, NSJP1-1 and SJP1-2 had the ability to solubilize dicalcium phosphate, produce siderophores, synthesize indole acetic acid, cellulose production, biofilm production, and root colonization. Inoculation of tomato plants with native Rhizobium strains influenced growth, fruit quality, and plant microbiome composition. Metagenomic analysis showed increased Proteobacteria abundance and altered alpha diversity indices, indicating changes in rhizospheric bacterial community.

Discussion

Our findings demonstrate the potential that native Rhizobium strains have to be used as a plant probiotic in agricultural crops for the generation of safe food and high nutritional value.

Application of the biogas residue of anaerobic co-digestion of gentamicin mycelial residues and wheat straw as soil amendment: Focus on nutrients supply, soil enzyme activities and antibiotic resistance genes

Land utilization of the biogas residue (BR) produced by anaerobic co-digestion of gentamicin mycelial residues (GMRs) and wheat straw is a promising method to achieve the deep recycling of GMRs. This study evaluated the feasibility and efficacy of application of using BR as a soil amendment by using a pot experiment. Results indicated that BR could improve the soil fertility better than commercial chicken manure fertilizer (CMF) in terms of the soil enzyme activities and nutrients supply. Random Forest (RF) model was applied to predict soil enzyme activities and identify key influencing factors. Combining the Random Forest (RF) model with the Three-dimensional Excitation-emission Matrix and Parallel Factor (3D-EEM-PARAFAC) analysis, revealing that humic-like substances provided by BR protected soil enzymes, thus improving soil fertility. Furthermore, gentamicin and antibiotic resistance genes (ARGs)/mobile genetic elements (MEGs) introduced by BR decreased greatly after cultivation, implying a low risk of antimicrobial resistance. This study suggested that reasonable application of BR could improve soil nutrients supply, soil enzyme activity and control antimicrobial resistance risk.

Copper and iron metal resistant rhizospheric bacteria boost the plant growth and bacoside A content in Bacopa monnieri under stress conditions

Bacteria that enhance plant growth and development and are found in the vicinity of roots are referred to as plant growth-promoting rhizobacteria. Some beneficial bacteria help plant tolerance to many hazardous chemical elements. In this context, Cupriavidus basilensis , Novosphingobium humi , Bacillus zanthoxyli , Bacillus sp., Paenibacillus alvei , Ancylobacter aquaticus and Ralstonia syzygii metal-tolerant rhizospheric bacteria were isolated from rhizospheric soil associated with Bacopa monnieri . The beneficial effects of rhizospheric bacteria on B. monnieri plant physiology and biochemical responses were investigated under pot conditions at two levels (100μM and 500μM) of CuSO4 or FeCl3 . N. humi , A. aquaticus and R. syzygii bacterial strains were associated with significantly increased height and biomass under normal and stress conditions. An assay for indole acetic acid in isolated rhizospheric bacteria found differential secretion except Bacillus zanthoxyli . Bacoside A is a major phytocompound in B. monnieri with medicinal value; maximum induction was observed in the R. syzygii treatment. High concentration of copper and iron salts negatively influenced height, biomass and photosynthetic pigments; however N. humi , A. aquaticus , Bacilllus sp. and R. syzygii beneficial bacterial helped plants under stress conditions. Moreover, a significant enhancement in chlorophyll a and b was noticed in C. basilensis , B. zanthoxyli , Bacilllus sp., P. alvei and R. syzygii treatments, without much influence on carotenoid levels. Therefore, the present study emphasises the importance of isolating plant growth-promoting rhizobacteria for use in bacopa plants exposed to metals such as copper and iron in soil.

Integrated use of plant growth-promoting bacteria and nano-zinc foliar spray is a sustainable approach for wheat biofortification, yield, and zinc use efficiency

Introduction and aims

The intensive cropping system and imbalance use of chemical fertilizers to pursue high grain production and feed the fast-growing global population has disturbed agricultural sustainability and nutritional security. Understanding micronutrient fertilizer management especially zinc (Zn) through foliar application is a crucial agronomic approach that could improve agronomic biofortification of staple grain crops. The use of plant growth-promoting bacteria (PGPBs) is considered as one of the sustainable and safe strategies that could improve nutrient acquisition and uptake in edible tissues of wheat to combat Zn malnutrition and hidden hunger in humans. Therefore, the objective of this study was to evaluate the best-performing PGPB inoculants in combination with nano-Zn foliar application on the growth, grain yield, and concentration of Zn in shoots and grains, Zn use efficiencies, and estimated Zn intake under wheat cultivation in the tropical savannah of Brazil.

Methods

The treatments consisted of four PGPB inoculations (without inoculation, Azospirillum brasilense, Bacillus subtilis, and Pseudomonas fluorescens, applied by seeds) and five Zn doses (0, 0.75, 1.5, 3, and 6 kg ha^-1, applied from nano ZnO in two splits by leaf).

Results

Inoculation of B. subtilis and P. fluorescens in combination with 1.5 kg ha^-1 foliar nano-Zn fertilization increased the concentration of Zn, nitrogen, and phosphorus in the shoot and grain of wheat in the 2019 and 2020 cropping seasons. Shoot dry matter was increased by 5.3% and 5.4% with the inoculation of P. fluorescens, which was statistically not different from the treatments with inoculation of B. subtilis as compared to control. The grain yield of wheat was increased with increasing nano-Zn foliar application up to 5 kg Zn ha^-1 with the inoculation of A. brasilense in 2019, and foliar nano-Zn up to a dose of 1.5 kg ha^-1 along with the inoculation of P. fluorescens in the 2020 cropping season. The zinc partitioning index was increased with increasing nano Zn application up to 3 kg ha^-1 along with the inoculation of P. fluorescens. Zinc use efficiency and applied Zn recovery were improved at low doses of nano-Zn application in combination with the inoculation of A. brasilense, B. subtilis, and P. fluorescens, respectively, as compared to control.

Discussion

Therefore, inoculation with B. subtilis and P. fluorescens along with foliar nano-Zn application is considered a sustainable and environmentally safe strategy to increase nutrition, growth, productivity, and Zn biofortification of wheat in tropical savannah.

Performance of Plant-Growth-Promoting Rhizobacteria (PGPR) Isolated from Sandy Soil on Growth of Tomato (Solanum lycopersicum L.)

The plant-growth-promoting rhizobacteria (PGPR) in the rhizosphere affect plant growth, health, and productivity, as well as soil-nutrient contents. They are considered a green and eco-friendly technology that will reduce chemical-fertilizer usage, thereby reducing production costs and protecting the environment. Out of 58 bacterial strains isolated in Qassim, Saudi Arabia, four strains were identified by the 16S rRNA as the Streptomyces cinereoruber strain P6-4, Priestia megaterium strain P12, Rossellomorea aquimaris strain P22-2, and Pseudomonas plecoglossicida strain P24. The plant-growth-promoting (PGP) features of the identified bacteria involving inorganic phosphate (P) solubilization, the production of indole acetic acid (IAA), and siderophore secretion were assessed in vitro. Regarding the P solubilization, the previous strains' efficacy reached 37.71%, 52.84%, 94.31%, and 64.20%, respectively. The strains produced considerable amounts of IAA (69.82, 251.70, 236.57, and 101.94 µg/mL) after 4 days of incubation at 30 °C. Furthermore, the rates of siderophore production reached 35.51, 26.37, 26.37, and 23.84 psu, respectively, in the same strains. The application of the selected strains in the presence of rock phosphate (RP) with tomato plants under greenhouse conditions was evaluated. The plant growth and P-uptake traits positively and significantly increased in response to all the bacterial treatments, except for some traits, such as plant height, number of leaves, and leaf DM at 21 DAT, compared to the negative control (rock phosphate, T2). Notably, the P. megaterium strain P12 (T4), followed by R. aquimaris strain P22-2 (T5), revealed the best values related to plant height (at 45 DAT), number of leaves per plant (at 45 DAT), root length, leaf area, leaf-P uptake, stem P uptake, and total plant P uptake compared to the rock phosphate. The first two components of the PCA (principal component analysis) represented 71.99% (PCA1 = 50.81% and PCA2 = 21.18%) of the variation at 45 DAT. Finally, the PGPR improved the vegetative-growth traits of the tomato plants through P solubilization, IAA, and siderophore production, and ameliorated the availability of nutrients. Thus, applying in PGPR in sustainable agriculture will potentially reduce production costs and protect the environment from contamination by chemical fertilizers and pesticides.

Comparison of the Rhizobacteria Serratia sp. H6 and Enterobacter sp. L7 on Arabidopsis thaliana Growth Promotion

The genera Serratia and Enterobacter belong to the Enterobacteriaceae family and several members have been described as plant growth-promoting rhizobacteria (PGPR). However, how these bacteria influence growth and development is unclear. We performed in vitro interaction assays between either Serratia sp. H6 or Enterobacter sp. L7 with Arabidopsis thaliana seedlings to analyze their effects on plant growth. In experiments of co-cultivation distant from the root tip, Enterobacter sp. decreased root length, markedly increased lateral root number, and slightly increased plant biomass by 33%, 230%, and 69%, respectively, and relative to the control. The volatile organic compounds (VOCs) emitted from Serratia sp. H6 but not those from Enterobacter sp. L7 promoted Arabidopsis growth. A blend of volatile compounds from the two bacteria had effects on plant growth that were similar to those observed for volatile compounds from H6 only. At several densities, the direct contact of roots with Serratia sp. H6 had phytostimulant properties but Enterobacter sp. L7 had clear deleterious effects. Together, these results suggest that direct contact and VOCs of Serratia sp. H6 were the main mechanisms to promote plant growth of A. thaliana, while diffusible compounds of Enterobacter sp. L7 were predominant in their PGPR activity.

Reconnoitering the capabilities of nodule endophytic Pantoea dispersa for improved nodulation and grain yield of chickpea (Cicer arietinum L.)

Microorganisms belonging to root and soil provide a wide range of services and benefits to the plant by promoting plant growth and controlling phytopathogens. This study aimed to isolate endophytic bacteria from the root nodules of chickpea (Cicer arietinum L.) and determine their potential in improving plant growth. A total of nineteen different bacterial morphotypes were isolated from root nodules of chickpea and characterized in vitro for plant growth promotion abilities. All bacterial isolates were able to produce indole acetic acid at varying levels, out of which MCA19 was screened as the most efficient indole acetic acid producer (10.25 µg mL^-1). MCA8, MCA9, MCA10, MCA11, MCA16, MCA17 and MCA19 were positive for phosphate solubilization, out of which MCA9 was best phosphate solubilizer (18.8 µg mL^-1). All bacterial strains showed varying ability to grow on nitrogen-free media. Hydrogen cyanide, pectinase, and cellulase production ability were also observed in isolates, in which MCA9, MCA12, MCA17 and MCA19 were found best. Based on in vitro testing, five isolates MCA2, MCA9, MCA11, MCA17 and MCA19 were selected for further studies. Bacterial isolates MCA9, MCA11, MCA17 and MCA19 were identified by 16S rRNA gene sequence analysis as Pantoea dispersa while MCA2 as Rhizobium pusense. This is the first report on the existence of Pantoea dispersa in the root nodules of chickpea. In pot experiment, a maximum increase of 30% was recorded in plant dry weight upon the application of MCA19. Under field conditions, bacterial isolates, MCA2, MCA11 and MCA19 significantly enhanced nodulation and yield parameters of chickpea, compared to control. Pantoea dispersa MCA19 displayed the highest plant growth-promoting potential by increasing 38% grain yield. Our results indicate that Pantoea dispersa MCA19 is a promising biofertilizer for future applications.

Plant growth promotion of the forage plant Lupinus albus Var. Orden Dorado using Pseudomonas agronomica sp. nov. and Bacillus pretiosus sp. nov. added over a valorized agricultural biowaste

Introduction

The overexploitation of natural ecosystems and the evolution of climate change currently force us to design new strategies for more sustainable agronomic uses. The recovery of plant residues, as an alternative to agrochemicals, can help alleviate these problems, for example, through its use for the synthesis of biofertilizers. In this work, the effect of the organic fertilizer matrix ORGAON^® from the valorization of horticultural waste is tested, to which two strains of bacteria (and their consortium) are added (SAICEU11^T identified as Bacillus pretiosus and SAICEU22^T identified as Pseudomonas agronomica), selected for their demonstrated ability to promote plant growth (PGPB), on the lupine forage plant (Lupinus albus).

Methods

For the synthesis of the biofertilizer, both strains were added to the ORGAON^® organic matrix separately, until reaching a final optical density (OD) of 0.5 McFarland in each case in the irrigation matrix. As a control, sterile ORGAON^® (ORGAON^®st) was used, also supplemented with the PGPB strains and a chemical fertilizer widely used in agronomy (Chem-F). With these treatments, a 6-week experiment was started under controlled laboratory conditions and on agricultural substrate, to recreate field conditions as accurately as possible. All the tests were carried out with 9 repetitions and 3 replicates of each treatment. After harvest, the improvements on the following biometric variables were studied for each treatment: total weight (Weight_T, g), shoot weight (Weight_S, g), root weight (Weight_R, g), number of leaves (Leaves, No.), shoot length (Length_S), root length (Length_R) and number of secondary roots (Roots, No.). Likewise, the identification of the tested strains and their description as new species was carried out. For this, they were studied from the phenotypic point of view (Transmission electron microscopy (TEM), metabolic profile, PGP activities, fatty acid profile and Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF)) and genotypic (sequencing of the main housekeeping genes and sequencing of the whole genome, genomic characteristics (dDDH and ANI) and phylogenetic analysis).

Results and discussion

After the statistical analysis of the results, it is shown that the individual addition of both strains on the ORGAON^® and ORGAON^®st organic matrix improve certain biometric variables. In the case of the SAICEU11T (Bacillus pretiosus) strain, the variables root weight (Weight_R, g), total weight (Weight_T, g) and length of the plant, and number of secondary roots (Roots, No.) significantly improve, while in the case of the strain SAICEU22^T (Pseudmonas agronomica), a significant improvement of root length (Length_R) and number of secondary roots (Roots, No.) is demonstrated. On the other hand, the genotaxonomic analysis showed that both species have not been described to date. The identification based on the main housekeeping genes, show that for the Bacillus strain (SAICEU11^T) the sequence similarity of the 16S rRNA was 100%, gyrB 92.69%, rpoB 97.70% and rpoD 94.67%. For the Pseudomonas strain (SAICEU22^T) the results were 100% for 16S rRNA, 98.43% for rpoD and 96.94% for gyrB. However, in both cases, the dDDH and ANI values, as well as the phylogenetic analysis, show that both species are below the species threshold, which would support the hypothesis that both are new species, in line with the chemotaxonomic results obtained by MALDI-TOF spectrometry and fatty acid profile. To verify the biosafety in their handling and release into the natural environment, we have ruled out the presence of genes that encode virulence factors or resistance to antibiotics, concluding that they are suitable for use in the field to improve the yield of crop plants. Type strains are SAICEU11T (= DSM 114702^T = CECT30674^T) for Bacillus pretiosus and SAICEU22^T (= DSM 114959^T = CECT30673^T) for Pseudomonas agronomicae.

The potential of lactic acid bacteria in mediating the control of plant diseases and plant growth stimulation in crop production - A mini review

The microbial diseases cause significant damage in agriculture, resulting in major yield and quality losses. To control microbiological damage and promote plant growth, a number of chemical control agents such as pesticides, herbicides, and insecticides are available. However, the rising prevalence of chemical control agents has led to unintended consequences for agricultural quality, environmental devastation, and human health. Chemical agents are not naturally broken down by microbes and can be found in the soil and environment long after natural decomposition has occurred. As an alternative to chemical agents, biocontrol agents are employed to manage phytopathogens. Interest in lactic acid bacteria (LAB) research as another class of potentially useful bacteria against phytopathogens has increased in recent years. Due to the high level of biosafety, they possess and the processes they employ to stimulate plant growth, LAB is increasingly being recognized as a viable option. This paper will review the available information on the antagonistic and plant-promoting capabilities of LAB and its mechanisms of action as well as its limitation as BCA. This review aimed at underlining the benefits and inputs from LAB as potential alternatives to chemical usage in sustaining crop productivity.

Diversity and function of soybean rhizosphere microbiome under nature farming

Nature farming is a farming system that entails cultivating crops without using chemical fertilizers and pesticides. The present study investigated the bacterial and fungal communities in the rhizosphere of soybean grown in conventional and nature farming soils using wild-type and non-nodulating mutant soybean. The effect of soil fumigant was also analyzed to reveal its perturbation of microbial communities and subsequent effects on the growth of soybean. Overall, the wild-type soybean exhibited a better growth index compared to mutant soybean and especially in nature farming. Nodulation and arbuscular mycorrhiza (AM) fungi colonization were higher in plants under nature farming than in conventionally managed soil; however, fumigation drastically affected these symbioses with greater impacts on plants in nature farming soil. The rhizosphere microbiome diversity in nature farming was higher than that in conventional farming for both cultivars. However, the diversity was significantly decreased after fumigation treatment with a greater impact on nature farming. Principal coordinate analysis revealed that nature farming and conventional farming soil harbored distinct microbial communities and that soil fumigation significantly altered the communities in nature farming soils but not in conventional farming soils. Intriguingly, some beneficial microbial taxa related to plant growth and health, including Rhizobium, Streptomyces, and Burkholderia, were found as distinct microbes in the nature farming soil but were selectively bleached by fumigant treatment. Network analysis revealed a highly complex microbial network with high taxa connectivity observed under nature farming soil than in conventional soil; however, fumigation strongly broke it. Overall, the results highlighted that nature farming embraced higher microbial diversity and the abundance of beneficial soil microbes with a complex and interconnected network structure, and also demonstrated the underlying resilience of the microbial community to environmental perturbations, which is critical under nature farming where chemical fertilizers and pesticides are not applied.

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.

Mitigating abiotic stress: microbiome engineering for improving agricultural production and environmental sustainability

The responses of plants to different abiotic stresses and mechanisms involved in their mitigation are discussed. Production of osmoprotectants, antioxidants, enzymes and other metabolites by beneficial microorganisms and their bioengineering ameliorates environmental stresses to improve food production. Progressive intensification of global agriculture, injudicious use of agrochemicals and change in climate conditions have deteriorated soil health, diminished the microbial biodiversity and resulted in environment pollution along with increase in biotic and abiotic stresses. Extreme weather conditions and erratic rains have further imposed additional stress for the growth and development of plants. Dominant abiotic stresses comprise drought, temperature, increased salinity, acidity, metal toxicity and nutrient starvation in soil, which severely limit crop production. For promoting sustainable crop production in environmentally challenging environments, use of beneficial microbes has emerged as a safer and sustainable means for mitigation of abiotic stresses resulting in improved crop productivity. These stress-tolerant microorganisms play an effective role against abiotic stresses by enhancing the antioxidant potential, improving nutrient acquisition, regulating the production of plant hormones, ACC deaminase, siderophore and exopolysaccharides and accumulating osmoprotectants and, thus, stimulating plant biomass and crop yield. In addition, bioengineering of beneficial microorganisms provides an innovative approach to enhance stress tolerance in plants. The use of genetically engineered stress-tolerant microbes as inoculants of crop plants may facilitate their use for enhanced nutrient cycling along with amelioration of abiotic stresses to improve food production for the ever-increasing population. In this chapter, an overview is provided about the current understanding of plant-bacterial interactions that help in alleviating abiotic stress in different crop systems in the face of climate change. This review largely focuses on the importance and need of sustainable and environmentally friendly approaches using beneficial microbes for ameliorating the environmental stresses in our agricultural systems.

Biological Control and Plant Growth Promotion Properties of Volatile Organic Compound-Producing Antagonistic Trichoderma spp

Trichoderma is environmentally vital due to their plant growth-promoting effects (such as enhancement of nutrients supply, suppression of plant pathogens, and promotion of plant defense). Biogenic volatile organic compounds (VOCs) are diverse chemical substances emitted by Trichoderma spp. The potential role of VOCs in biological control and plant growth promotion has recently been recognized. Here, the Trichoderma-VOCs' performance for plant growth promotion and suppression of plant pathogens are evaluated. We further investigated VOC emission profiles of T. harzianum using GC-MS. The Trichoderma-VOCs exhibited significant (p < 0.05) antifungal properties against all tested pathogenic fungi. T. atroviride-VOCs showed a decisive inhibition of Alternaria panax, Botrytis cinerea, Cylindrocarpon destructans, and Sclerotinia nivalis. The germinating seeds demonstrated growth enhancement in the presence of Trichoderma-VOCs emitted by different strains. Low levels of cyclopentasiloxane, decamethyl, cyclotetrasiloxane, and octamethyl were found in T. harzianum KNU1 strain whereas cyclopentasiloxane, decamethyl, cyclotetrasiloxane, and octamethyl showed higher emission levels as Si-containing compounds. The results reveal the potentiality of VOCs as a biocontrol resource against deleterious rhizosphere microorganisms and underline the importance of Trichoderma-VOCs emissions in regulating plant growth and development.

Perspectives on Converting Keratin-Containing Wastes Into Biofertilizers for Sustainable Agriculture

Keratin-containing wastes become pollution to the environment if they are not treated properly. On the other hand, these wastes can be converted into value-added products applicable to many fields. Organic fertilizers and biofertilizers are important for sustainable agriculture by providing nutrients to enhance the growth speed of the plant and production. Keratin-containing wastes, therefore, will be an important resource to produce organic fertilizers. Many microorganisms exhibit capabilities to degrade keratins making them attractive to convert keratin-containing wastes into valuable products. In this review, the progress in microbial degradation of keratins is summarized. In addition, perspectives in converting keratin into bio- and organic fertilizers for agriculture are described. With proper treatment, feather wastes which are rich in keratin can be converted into high-value fertilizers to serve as nutrients for plants, reduce environmental pressure and improve the quality of the soil for sustainable agriculture.

Potential role of rhizobia to enhance chickpea-growth and yield in low fertility-soils of Tunisia

Plant growth-promoting rhizobacteria are bacteria that improve plant growth and reduce plant pathogen damages. In this study, 100 nodule bacteria were isolated from chickpea, screened for their plant growth-promoting (PGP) traits and then characterised by PCR-RFLP of 16 S rDNA. Results showed that most of the slow-growing isolates fixed nitrogen but those exhibiting fast-growth did not. Fourteen isolates solubilized inorganic phosphorus, 16 strains produced siderophores, and 17 strains produced indole acetic acid. Co-culture experiments identified three strains having an inhibitory effect against Fusarium oxysporum, the primary pathogenic fungus for chickpea in Tunisia. Rhizobia with PGP traits were assigned to Mesorhizobium ciceri, Mesorhizobium mediterraneum, Sinorhizobium meliloti and Agrobacterium tumefaciens. We noted that PGP activities were differentially distributed between M. ciceri and M. mediterraneum. The region of Mateur in northern Tunisia, with clay-silty soil, was the origin of 53% of PGP isolates. Interestingly, we found that S. meliloti and A. tumefaciens strains did not behave as parasitic nodule-bacteria but as PGP rhizobacteria useful for chickpea nutrition and health. In fact, S. meliloti strains could solubilize phosphorus, produce siderophore and auxin. The A. tumefaciens strains could perform the previous PGP traits and inhibit pathogen growth also. Finally, one candidate strain of M. ciceri (LL10)-selected for its highest symbiotic nitrogen fixation and phosphorus solubilization-was used for field experiment. The LL10 inoculation increased grain yield more than three-fold. These finding showed the potential role of rhizobia to be used as biofertilizers and biopesticides, representing low-cost and environment-friendly inputs for sustainable agriculture.

Rhizophagus irregularis and Nitrogen Fixing Azotobacter with a Reduced Rate of Chemical Fertilizer Application Enhances Pepper Growth along with Fruits Biochemical and Mineral Composition

Bell pepper is an important vegetable crop containing lots of bioactive compounds. The present study was designed to improve the productivity and quality of bell pepper with the application of arbuscular mycorrhizal fungi (Rhizophagus irregularis) and plant growth-promoting bacteria (Azotobacter chroococcum) in a combination of chemical fertilizer. Five treatments consisted of 75% chemical fertilizer (T1), 100% chemical fertilizer (T2), 75% chemical fertilizer + R. irregularis (T3), 75% chemical fertilizer + A. chroococcum (T4) and 75% chemical fertilizer + R. irregularis + A. chroococcum (T5). Out of 18 morphological parameters, 11 morphometric fruit parameters were recorded in detail by a tomato analyzer. The morphological and biochemical (TSS, ascorbic acid and capsaicin content) attributes of bell pepper were recorded higher in the case of a mixed consortium of chemical fertilizers having R. irregularis and A. chroococcum. Similarly, the amount of mineral content recorded was highest after 75% chemical fertilizer + R. irregularis + A. chroococcum, followed by the treatment with only 100% chemical fertilizer. The root mycorrhization (%) and the number of spores were observed highest in 75% chemical fertilizer + R. irregularis + A. chroococcum, and there was no mycorrhization and spore formation in 75% CF, 100% CF and 75% CF+AC. The treatment involving 75% chemical fertilizer + R. irregularis + A. chroococcum proved better for pepper’s growth, yield and yield-related traits.

New Polyfunctional Biorationals Use to Achieve Competitive Yield of Organic Potatoes in the North-West Russian Ecosystem

To increase the organic potato yield, it is necessary to provide the crop with sufficient nutrients and effective means of biocontrol the diseases. The research goal was to characterize the biorationals’ efficacy to achieve competitive organic potatoes’ yield under various weather conditions. A 4-year trial was carried out in the Leningrad region using Udacha variety potatoes. The tests used liquid forms of new polyfunctional biologicals Kartofin based on highly active Bacillus subtilis I-5-12/23 and organic fertilizer BIAGUM obtained from poultry manure by aerobic fermentation in a closed biofermenter. Significant stimulation in plant growth and development to the flowering phase regardless of the hydrothermal conditions of the growing season was noted. The stimulating effect was determined by the combined use of biorationals pro rata to BIAGUM dose. Kartofin biologicals and BIAGUM almost doubled the potato tubers’ yield compared to the control, regardless of the growing season conditions. At the flowering phase, the biological efficacy in potato fungal diseases incidence and development was near 90% under optimal and 50–75% under drought hydrothermal conditions. At the end of vegetation, the efficiency in fungal diseases incidence and development made up 45–65% under optimal and 45–70% under dry conditions. BIAGUM effectiveness in reducing disease development reached 45–50% regardless of growing season conditions.

Fertilization and Soil Microbial Community: A Review

The present paper reviews the most recent advances regarding the effects of chemical and organic fertilizers on soil microbial communities. Based on the results from the articles considered, some details are presented on how the use of various types of fertilizers affects the composition and activity of soil microbial communities. Soil microbes have different responses to fertilization based on differences in the total carbon (C), nitrogen (N) and phosphorus (P) contents in the soil, along with soil moisture and the presence of plant species. These articles show that the use of chemical fertilizers changes the abundance of microbial populations and stimulates their growth thanks to the nutrient supply added. Overall, however, the data revealed that chemical fertilizers have no significant influence on the richness and diversity of the bacteria and fungi. Instead, the abundance of individual bacterial or fungal species was sensitive to fertilization and was mainly attributed to the changes in the soil chemical properties induced by chemical or organic fertilization. Among the negative effects of chemical fertilization, the decrease in enzymatic activity has been highlighted by several papers, especially in soils that have received the largest amounts of fertilizers together with losses in organic matter.