Growth-promoting Microorganisms Research Articles

The effect of long-term controlled-release urea application on the relative abundances of plant growth-promoting microorganisms

Controlled-release urea (CRUs), including polymer-coated urea (PCU), sulfur-coated urea (SCU), and polymer/sulfur dual layer-coated urea (PSCU), have been demonstrated to increase crop yield and nitrogen use efficiency (NUE). However, the effects of long-term application of CRUs on soil microbial community and function remain unclear. In this study, a 12-year (2009–2021) 24-season wheat -maize rotation lysimeter experiment was studied to investigate the effects of PCU, SCU, and PSCU on soil microbial community composition and function. Wheat was grown, soil chemical properties were analyzed, and soil biological properties including enzyme activities and microbial community structure and function at the wheat filling stage were determined in 2021. The results showed that soil organic matter (SOM) contents were markedly increased by 3.1∼5.0% under the CRUs compared to conventional urea. Meanwhile, some carbon, nitrogen, and sulfur cycle enzyme activities, including cellulase (CE), urease and arylsulfatase (AS), were significantly enhanced by 23.4∼32.4%, 6.6∼32.1%, and 2.5∼3.7% under the CRUs compared to conventional urea, respectively. Redundancy analysis indicated that changes in bacterial and fungal communities were driven by SOM. Co-occurrence network analysis showed that wheat growth promotion by the CRUs was strongly linked to the high relative abundance (Z-score) of bacterial and fungal module 1, which included such plant growth-promoting microorganisms (PGPMs) as Arthrobacter, Bryobacter, Bradyrhizobium, Microscypha, and Marasmius. Compared with PCU, SCU and PSCU showed a better effect in increasing the relative abundances of PGPMs while inhibiting the growth of nitrobacteria, denitrifying bacteria, and plant pathogens, thereby better promoting wheat yields and reducing N loss and plant disease. Of the three CRUs, SCU and PSCU have significantly increased SOM, which provided sufficient substrate for the growth of PGPMs, thus increasing wheat yield. This study provides a support for long-term CRUs application and sustainable agriculture.

MAIZE SEED INOCULATION WITH BIOAGENT AND ITS EFFECTS ON THE GROWTH AND YIELD TRAITS

The presented study sought to use the plant growth-promoting microorganism (PGPM) as a biofertilizer in maize (Zea mays L.) seeds and determine its effects on the growth and productivity of maize, with two levels of mineral fertilizer (25% and 50% of chemical fertilizer) under Iraqi conditions. Laboratory studies confirmed no antagonism between Azotobacter chroococcum and other microorganisms used in this study. Field experiments carried out during crop season 2021 were in two different regions, Mosul (36°20′6″N, 43°7′8″E) and Kirkuk (35°28′5.02″N, 44°23′31.99″E) in the north of Iraq. The result showed biofertilizer superiority when combined with 25% and 50% doses of the recommended mineral fertilizer for maize growth and yield traits in the experiments in both locations. In Kirkuk city, the biofertilizer combined with 25% chemical fertilizer recorded superiority without significant difference from the biofertilizer combined with 50% mineral fertilizer. However, in Mosul city, the biofertilizer combined with 50% chemical fertilizer expressed a more superior and significant difference than other treatments for growth and yield traits in maize. The difference between the two regions might be due to chemical fertilizer residues in the soil.

Microbial Biofertilisers in Plant Production and Resistance: A Review

In sustainable agriculture, plant nutrients are the most important elements. Biofertilisers introduce microorganisms that improve the nutrient status of plants and increase their accessibility to crops. To meet the demands of a growing population, it is necessary to produce healthy crops using the right type of fertilisers to provide them with all the key nutrients they need. However, the increasing dependence on chemical fertilisers is destroying the environment and negatively affecting human health. Therefore, it is believed that the use of microbes as bioinoculants, used together with chemical fertilisers, is the best strategy to increase plant growth and soil fertility. In sustainable agriculture, these microbes bring significant benefits to crops. In addition to colonising plant systems (epiphytes, endophytes and rhizospheres), beneficial microbes play a key role in the uptake of nutrients from surrounding ecosystems. Microorganisms, especially fungi, also play a protective function in plants, enhancing the responses of defence systems, and play a key role in situations related to soil iron deficiency or phosphorous solubilisation. Plant-associated microbes can thus promote plant growth regardless of natural and extreme conditions. The most frequently used strategies for growth-promoting microorganisms are nitrogen fixation, the production of growth hormones, siderophores, HCN, various hydrolytic enzymes and the solubilisation of potassium, zinc and phosphorous. Research on biofertilisers has been extensive and available, demonstrating how these microbes can provide crops with sufficient nutrients to increase yields. This review examines in detail the direct and indirect mechanisms of PGPR action and their interactions in plant growth and resistance.

Growth-promoting microorganisms in the development of orchid seedlings of Phalaenopsis, Cymbidium, and Dendrobium genera

The demand for sustainable agricultural production systems is increasing, and using growth-promoting microorganisms in plants has stood out because it decreases or even replaces chemical fertilizer use, reducing production costs. This study aimed to evaluate the response of some microorganisms applied to the seedlings of primary orchids cultivated in Brazil (Phalaenopsis sp. 'Taisuco Swan', Cymbidium atropurpureum, and Dendrobium secundum). The experimental design was completely randomized. There were seven treatments (absence of microorganisms – control, Trichoderma sp. in sodium alginate, Trichoderma sp. in clay, Trichoderma sp. in sodium alginate and clay, Trichoderma sp. in a liquid medium, Azospirillum brasilense + Bacillus subtilis in a liquid medium, and Bacillus pumilus in a liquid medium), four replications, and three plants per plot. The seedlings were grown in a greenhouse and evaluated 190 days after microorganism inoculation. The evaluation of morpho-physiological characteristics differed according to the particularities of each genus. The Bacillus pumilus and Azospirillum brasilense + Bacillus subtilis rhizobacteria in a liquid medium for Phalaenopsis sp. 'Taisuco Swan' and the Trichoderma sp. fungus in a liquid medium for Cymbidium atropurpureum increased seedling growth and development. Azospirillum brasilense + Bacillus subtilis in a liquid medium for the Dendrobium secundum orchid promoted more root biomass. Using beneficial microorganisms in orchid cultivation is promising, and seedling growth and development depend on their inoculation and the morpho-physiological characteristics of each plant.

The shaping of onion seedlings performance through substrate formulation and co-inoculation with beneficial microorganism consortia.

Smart management in crop cultivation is increasingly supported by application of arbuscular mycorrhizal fungi (AMF) and plant growth-promoting microorganisms (PGPM), which sustain soil fertility and plant performance. The aim of this study was the evaluation of the effects of consortia composed of (Claroideoglomus claroideum BEG96, Claroideoglomus etunicatum BEG92, Funneliformis geosporum BEG199, Funneliformis mosseae BEG 95, and Rhizophagus irregularis BEG140) and PGPM (Azospirillum brasilense - AZ, or Saccharothrix sp. - S) on onion cultivated in growing media with a composition corresponding to a degraded soil. Three types of substrate formulations were used, with peat:sand ratios of 50:50, 70:30, 100:0 (v:v). The analysis of substrate parameters crucial for its fertility (pH, salinity, sorption complex capacity, and elements' content) and characteristics reflecting onion seedlings' performance (fresh weight, stress biomarkers, and elements' content) was performed. AMF colonized onion roots in all treatments, showing increasing potential to form intercellular structures in the substrates rich in organic matter. Additionally, co-inoculation with PGPM microorganisms accelerated arbuscular mycorrhiza establishment. Increased antioxidant activity and glutathione peroxidase (GPOX) activity of onion roots sampled from the formulations composed of peat and sand in the ratio of 100:0, inoculated with AMF+S, and positive correlation between GPOX, fresh weight and antioxidant activity of onion roots reflected the successful induction of plant acclimatization response. Total phenols content was the highest in roots and leaves of onion grown in substrates with 70:30 peat:sand ratio, and, in the case of roots, it was correlated with AMF colonization parameters but not with antioxidant activity. AMF and PGPM efficiency in supporting onion growth should be linked to the increased onion root system capacity in mineral salts absorption, resulting in more efficient aboveground biomass production. AMF and PGPM consortia were effective in releasing minerals to soluble fraction in substrates rich in organic matter, making elements available for uptake by onion root system, though this phenomenon depended on the PGPM species. Microorganism consortia enhanced onion seedlings' performance also in substrates with lower content of organic carbon through plant biofertilization and phytostimulation.

Indigenously produced biochar retains fertility in sandy soil through unique microbial diversity sustenance: a step toward the circular economy.

Agricultural productivity in the arid hot desert climate of UAE is limited by the unavailability of water, high temperature, and salt stresses. Growing enough food under abiotic stresses and decreasing reliance on imports in an era of global warming are a challenge. Biochar with high water and nutrient retention capacity and acid neutralization activity is an attractive soil conditioner. This study investigates the microbial community in the arid soil of Dubai under shade house conditions irrigated with saline water and the shift in the microbial community, following 1 year of amendment with indigenously prepared biochar from date palm waste. Amplicon sequencing was used to elucidate changes in bacterial, archaeal, and fungal community structures in response to long-term biochar amendment. Samples were collected from quinoa fields receiving standard NPK doses and from fields receiving 20 and 30 tons ha-1 of biochar, in addition to NPK for 1 year. Water holding capacity, pH, electrical conductivity, calcium, magnesium, chloride, potassium, sodium, phosphorus, total carbon, organic matter, and total nitrogen in the soil from biochar-treated and untreated controls were determined. The results show that soil amendment with biochar helps retain archaeal and bacterial diversity. Analysis of differentially abundant bacterial and fungal genera indicates enrichment of plant growth-promoting microorganisms. Interestingly, many of the abundant genera are known to tolerate salt stress, and some observed genera were of marine origin. Biochar application improved the mineral status and organic matter content of the soil. Various physicochemical properties of soil receiving 30 tons ha-1 of biochar improved significantly over the control soil. This study strongly suggests that biochar helps retain soil fertility through the enrichment of plant growth-promoting microorganisms.

Disclosing the native blueberry rhizosphere community in Portugal-an integrated metagenomic and isolation approach.

The production of red fruits, such as blueberry, has been threatened by several stressors from severe periods of drought, nutrient scarcity, phytopathogens, and costs with fertilization programs with adverse consequences. Thus, there is an urgent need to increase this crop's resilience whilst promoting sustainable agriculture. Plant growth-promoting microorganisms (PGPMs) constitute not only a solution to tackle water and nutrient deficits in soils, but also as a control against phytopathogens and as green compounds for agricultural practices. In this study, a metagenomic approach of the local fungal and bacterial community of the rhizosphere of Vaccinium corymbosum plants was performed. At the same time, both epiphytic and endophytic microorganisms were isolated in order to disclose putative beneficial native organisms. Results showed a high relative abundance of Archaeorhizomyces and Serendipita genera in the ITS sequencing, and Bradyrhizobium genus in the 16S sequencing. Diversity analysis disclosed that the fungal community presented a higher inter-sample variability than the bacterial community, and beta-diversity analysis further corroborated this result. Trichoderma spp., Bacillus spp., and Mucor moelleri were isolated from the V. corymbosum plants. This work revealed a native microbial community capable of establishing mycorrhizal relationships, and with beneficial physiological traits for blueberry production. It was also possible to isolate several naturally-occurring microorganisms that are known to have plant growth-promoting activity and confer tolerance to hydric stress, a serious climate change threat. Future studies should be performed with these isolates to disclose their efficiency in conferring the needed resilience for this and several crops.

Legacy effects of rhizodeposits on soil microbiomes: A perspective

Plant legacy effects observed in plant-soil feedback experiments have largely been attributed to the root or litter material of the previous plant. The legacy effects of rhizodeposits are defined as changes in the soil microbiome that remain after a plant has died or been removed from the soil and caused by the release of substances of various compositions by living plants (rhizodeposits). Rhizodeposit-mediated legacy effects have been largely ignored mainly due to the high spatial and temporal variability of rhizodeposits and difficulties quantifying and tracking them in the rhizosphere. In this perspective article, we discuss what is known about the legacy effects of rhizodeposits and provide ideas for future experiments to improve understanding of this phenomenon. Only a few studies separate rhizodeposit-mediated plant legacy effects from legacy effects of root decomposition. Results from these experiments indicate that rhizodeposit-mediated legacy effects on soil microbial communities may persist for several months to several years, especially if the same crop is cultivated persistently for several years in a ‘conditioning’ phase. Rhizodeposit-mediated legacy effects on fungal communities usually last longer than those on bacterial communities due to fungal life-cycle strategies (spore formation) and slower reproduction rates, compared to bacterial communities. We highlight the need for further experimentation to investigate the influence that the length of a conditioning phase has on the persistence of the legacy effect, differentiate the effect of root exudates from the effects of sloughed root cells, separate the influence of simple sugars from that of high molecular-weight exudates and plant derived compounds with antimicrobial properties, and explore whether plant species diversity influences the nature of the legacy. To address these questions, we propose the use of contemporary tools such as stable isotope probing, plant genetics, and reverse microdialysis. We think that harnessing rhizodeposit-mediated plant legacy effects could be a promising approach to improve sustainable crop production by creating disease-suppressive soils and simulating plant growth-promoting micro-organisms within soil systems.

Screening microbial inoculants and their interventions for cross-kingdom management of wilt disease of solanaceous crops- a step toward sustainable agriculture.

Microbial inoculants may be called magical bullets because they are small in size but have a huge impact on plant life and humans. The screening of these beneficial microbes will give us an evergreen technology to manage harmful diseases of cross-kingdom crops. The production of these crops is reducing as a result of multiple biotic factors and among them the bacterial wilt disease triggered by Ralstonia solanacearum is the most important in solanaceous crops. The examination of the diversity of bioinoculants has shown that more microbial species have biocontrol activity against soil-borne pathogens. Reduced crop output, lower yields, and greater cost of cultivation are among the major issues caused by diseases in agriculture around the world. It is universally true that soil-borne disease epidemics pose a greater threat to crops. These necessitate the use of eco-friendly microbial bioinoculants. This review article provides an overview of plant growth-promoting microorganisms bioinoculants, their various characteristics, biochemical and molecular screening insights, and modes of action and interaction. The discussion is concluded with a brief overview of potential future possibilities for the sustainable development of agriculture. This review will be useful for students and researchers to obtain existing knowledge of microbial inoculants, their activities, and their mechanisms, which will facilitate the development of environmentally friendly management strategies for cross-kingdom plant diseases.

The Effect of Nutrient Source and Beneficial Bacteria on Growth of Pythium-Exposed Lettuce at High Salt Stress

High salinity, nutrient imbalance, and pathogens are some of the challenges of closed soilless cultivation systems, e.g., those combining hydroponics (HP) with aquaculture effluents (AE). Plant growth-promoting microorganisms (PGPM) can support plants to cope with stressing agents. To address these topics, lettuces were grown in soilless systems (20 boxes) at an electrical conductivity of around 4.2–5 mS/cm, following a full factorial design with two nutrient sources and five bacterial treatments. The nutrient sources were either organic (AE) or inorganic (HP); the treatments were either commercial PGPM or sludges of an aquaculture farm or of an urban wastewater treatment plant. Finally, half the plants were exposed to pathogen Pythium sp. After 61 days of culture, most of the differences between HP- and AE-plants could be attributed to the composition of the nutrient solutions. Nutrient imbalances, salinity, and the pathogen exposition did not cause severe damage, except for tip burn. Fresh weight was significantly higher in HP (177.8 g) than in AE (107.0 g), while the chlorophyll and flavonoid levels tended to be higher in AE. The leaf sodium and chlorine concentrations were higher than the values found in similar studies; however, AE plants contained a lower content of sodium and chlorine (35.0 and 21.5 mg/g dry weight) than the HP ones (44.6 and 28.6 mg/g dry weight). Many macro- and micronutrients in the AE-grown plants tended to be higher when the commercial PGPM or the sludges were administered, supporting the idea that those treatments contain a flora that helps to extract nutrients from organic sources. The study demonstrated that lettuce can be successfully cultured at relatively high salt concentration. To further investigate beneficial services such as nutrient extraction, salinity mitigation, and pathogen protection, we suggest administering bacterial communities of known composition, or single microbial strains. The study also showed that PGPM can be found in sludges of different origins; isolating beneficial strains from sludge would additionally transform its management from a burdensome cost to a source of beneficial services.

Utilização de microrganismos multifuncionais na cultura do milho

ABSTRACT In the composition of the soil microbiome, there are numerous microorganisms capable of promoting plant growth, better known as plant growth-promoting microorganisms. The study aimed to determine the effects of multifunctional microorganisms, alone or in combination, on shoot, root, and total biomass production, gas exchange, macronutrient content, yield components, and grain yield of corn plants. The experiment was carried out in a greenhouse in a completely randomized design, with four replications. Twenty-six treatments consisted of isolated or combined microbiolization of corn seeds with the rhizobacteria Bacillus sp. (BRM 32109, BRM 32110, and BRM 63573), Burkholderia cepacea (BRM 32111), Pseudomonas sp. (BRM 32112), Serratia marcenses BRM 32113, Serratia sp. (BRM 32114), Azospirillum brasilense (Ab-V5), and Azospirillum sp. (BRM 63574), an isolated of fungus Trichoderma koningiopsis (BRM 53736), and a control treatment (without the application of microorganisms). At seven and 21 days, two more applications of the same treatments were carried out in the soil and the plants, respectively. The microorganisms applied alone or in combination promoted significant increases of 49% in corn plant biomass, 30% in gas exchange, 36% in macronutrient content, and 33% in grain yield. Isolates BRM 32114, Ab-V5, BRM 32110, and BRM 32112 and the combinations BRM 32114 + BRM 53736, BRM 63573 + Ab-V5, and BRM 32114 + BRM 32110 promoted better benefits to corn, allowing us to infer that the use of beneficial microorganisms significantly affects the development of corn plants.

Apple Root Microbiome as Indicator of Plant Adaptation to Apple Replant Diseased Soils.

The tree fruit industry in Nova Scotia, Canada, is dominated by the apple (Malus domestica) sector. However, the sector is faced with numerous challenges, including apple replant disease (ARD), which is a well-known problem in areas with intensive apple cultivation. A study was performed using 16S rRNA/18S rRNA and 16S rRNA/ITS2 amplicon sequencing to assess soil- and root-associated microbiomes, respectively, from mature apple orchards and soil microbiomes alone from uncultivated soil. The results indicated significant (p < 0.05) differences in soil microbial community structure and composition between uncultivated soil and cultivated apple orchard soil. We identified an increase in the number of potential pathogens in the orchard soil compared to uncultivated soil. At the same time, we detected a significant (p < 0.05) increase in relative abundances of several potential plant-growth-promoting or biocontrol microorganisms and non-fungal eukaryotes capable of promoting the proliferation of bacterial biocontrol agents in orchard soils. Additionally, the apple roots accumulated several potential PGP bacteria from Proteobacteria and Actinobacteria phyla, while the relative abundances of fungal taxa with the potential to contribute to ARD, such as Nectriaceae and plant pathogenic Fusarium spp., were decreased in the apple root microbiome compared to the soil microbiome. The results suggest that the health of a mature apple tree can be ascribed to a complex interaction between potential pathogenic and plant growth-promoting microorganisms in the soil and on apple roots.

Comparative Genomics and Physiological Investigations Supported Multifaceted Plant Growth-Promoting Activities in Two Hypericum perforatum L.-Associated Plant Growth-Promoting Rhizobacteria for Microbe-Assisted Cultivation.

Plants are no longer considered standalone entities; instead, they harbor a diverse community of plant growth-promoting rhizobacteria (PGPR) that aid them in nutrient acquisition and can also deliver resilience. Host plants recognize PGPR in a strain-specific manner; therefore, introducing untargeted PGPR might produce unsatisfactory crop yields. Consequently, to develop a microbe-assisted Hypericum perforatum L. cultivation technique, 31 rhizobacteria were isolated from the plant's high-altitude Indian western Himalayan natural habitat and in vitro characterized for multiple plant growth-promoting attributes. Among 31 rhizobacterial isolates, 26 produced 0.59 to 85.29 μg mL-1 indole-3-acetic acid and solubilized 15.77 to 71.43 μg mL-1 inorganic phosphate; 21 produced 63.12 to 99.92% siderophore units, and 15 exhibited 103.60 to 1,296.42 nmol α-ketobutyrate mg-1 protein h-1 1-aminocyclopropane-1-carboxylate deaminase (ACCD) activity. Based on superior plant growth-promoting attributes, eight statistically significant multifarious PGPR were further evaluated for an in planta plant growth-promotion assay under poly greenhouse conditions. Plants treated with Kosakonia cowanii HypNH10 and Rahnella variigena HypNH18 showed, by significant amounts, the highest photosynthetic pigments and performance, eventually leading to the highest biomass accumulation. Comparative genome analysis and comprehensive genome mining unraveled their unique genetic features, such as adaptation to the host plant's immune system and specialized metabolites. Moreover, the strains harbor several functional genes regulating direct and indirect plant growth-promotion mechanisms through nutrient acquisition, phytohormone production, and stress alleviation. In essence, the current study endorsed strains HypNH10 and HypNH18 as cogent candidates for microbe-assisted H. perforatum cultivation by highlighting their exclusive genomic signatures, which suggest their unison, compatibility, and multifaceted beneficial interactions with their host and support the excellent plant growth-promotion performance observed in the greenhouse trial. IMPORTANCE Hypericum perforatum L. (St. John's wort) herbal preparations are among the top-selling products to treat depression worldwide. A significant portion of the overall Hypericum supply is sourced through wild collection, prompting a rapid decline in their natural stands. Crop cultivation seems lucrative, although cultivable land and its existing rhizomicrobiome are well suited for traditional crops, and its sudden introduction can create soil microbiome dysbiosis. Also, the conventional plant domestication procedures with increased reliance on agrochemicals can reduce the diversity of the associated rhizomicrobiome and plants' ability to interact with plant growth-promoting microorganisms, leading to unsatisfactory crop production alongside harmful environmental effects. Cultivating H. perforatum with crop-associated beneficial rhizobacteria can reconcile such concerns. Based on a combinatorial in vitro, in vivo plant growth-promotion assay and in silico prediction of plant growth-promoting traits, here we recommend two H. perforatum-associated PGPR, Kosakonia cowanii HypNH10 and Rahnella variigena HypNH18, to extrapolate as functional bioinoculants for H. perforatum sustainable cultivation.

Acclimatisation of orchids using plant growth-promoting bacteria and humic acids

ABSTRACT Acclimatisation of orchid seedlings propagated in vitro is a slow process that can be accelerated with the use of plant growth-promoting microorganisms and humic substances. The aim of this study was to evaluate the plant’s response to inoculation with plant growth-promoting bacteria and humic acids, as well as to their combined use, during the period of acclimatisation of Cymbidium sp. orchids. The treatments were control; application of humic acids; inoculation with Stenotrophomonas maltophilia; inoculation with Burkholderia cepacia; inoculation with S. maltophilia and B. cepacia; inoculation with S. maltophilia combined with application of humic acids; inoculation with B. cepacia combined with application of humic acids; inoculation with S. maltophilia and B. cepacia combined with application of humic acids. A total of 150 days after acclimatisation, the plants were biometrically and nutritionally evaluated. Inoculation with the bacterial strains separately promoted seedlings with greater N content; however, only inoculation with S. maltophilia, resulted in plants with more total dry matter in relation to the control. There was no response from application of humic acids in an isolated manner or in combination with the bacterial strains. The results indicate the biotechnological potential of the bacteria S. maltophilia in promoting the growth of the Cymbidium sp. orchid.

Mitigation of Salinity Stress on Soybean Seedlings Using Indole Acetic Acid-Producing Acinetobacter pittii YNA40

Soybean is an important oil crop with multiple uses. Soybeans can grow in various soil types and climates; however, salt stress reduces their yield. Plant growth-promoting microorganisms are an environmentally benign way to combat stress and boost plant tolerance. In the present study, we have identified plant growth-promoting bacteria that can produce indole acetic acid (IAA) and induce distinct growth characteristics in soybean plants under salt stress. The YNA40 isolate was identified as Acinetobacter pittii through 16S rRNA sequencing and phylogenetic analysis. A pure culture of Acinetobacter pittii YNA40 was subjected to chromatographic and mass spectrometry selected-ion monitoring (GC-MS/SIM) for IAA quantification. The results revealed that the YNA40 bacterial strain showed a significantly higher IAA concentration (473.88 ng/mL) at 4% sodium chloride (NaCl). Moreover, in a salt-stress condition, inoculation with Acinetobacter pittii YNA40 was able to induce increased shoot length (23.48%), shoot weight (24%), root length (2.47%), and root weight (44.82%) compared to the uninoculated control. Therefore, soybean seedlings were inoculated with YNA40 to examine their potential for promoting growth and reprogramming after salt stress. Inoculation with YNA40 isolates mitigated the salt stress and significantly improved the growth of the plant, enhanced the chlorophyll contents, and improved the quantum efficiency of chlorophyll fluorescence, total phenolic content, flavonoid content, the diphenyl-1-picrylhydrazyl (DPPH) activity, and antioxidant activities of soybean plants during and after salt stress. The present research demonstrated that the application of the YNA40 isolate is promising for reducing salt stress in soybean plants and helps plants grow better in a salt-stressed environment.

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

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

Beneficial Microorganisms Improve Agricultural Sustainability under Climatic Extremes.

The challenging alterations in climate in the last decades have had direct and indirect influences on biotic and abiotic stresses that have led to devastating implications on agricultural crop production and food security. Extreme environmental conditions, such as abiotic stresses, offer great opportunities to study the influence of different microorganisms in plant development and agricultural productivity. The focus of this review is to highlight the mechanisms of plant growth-promoting microorganisms (especially bacteria and fungi) adapted to environmental induced stresses such as drought, salinity, heavy metals, flooding, extreme temperatures, and intense light. The present state of knowledge focuses on the potential, prospective, and biotechnological approaches of plant growth-promoting bacteria and fungi to improve plant nutrition, physio-biochemical attributes, and the fitness of plants under environmental stresses. The current review focuses on the importance of the microbial community in improving sustainable crop production under changing climatic scenarios.

Editorial: Plant growth-promoting microorganisms for sustainable agricultural production, volume II

Editorial: Plant growth-promoting microorganisms for sustainable agricultural production, volume II

Introducing the Power of Plant Growth Promoting Microorganisms in Soilless Systems: A Promising Alternative for Sustainable Agriculture

Soilless systems, such as hydroponics and aquaponics, are gaining popularity as a sustainable alternative to traditional soil-based agriculture, aiming at maximizing plant productivity while minimizing resource use. Nonetheless, the absence of a soil matrix poses challenges that require precise management of nutrients, effective control of salinity stress, and proactive strategies to master disease management. Plant growth-promoting microorganisms (PGPM) have emerged as a promising solution to overcome these issues. Research demonstrated that Bacillus, Pseudomonas, and Azospirillum are the most extensively studied genera for their effectiveness as growth promoters, inducing changes in root architecture morphology. Furthermore, PGPM inoculation, either alone or in synergy, can reverse the effects of nutrient deficiency and salt stress. The genera Pseudomonas and Trichoderma were recognized for their solid antagonistic traits, which make them highly effective biocontrol agents in hydroponic systems. The latest findings indicate their ability to significantly reduce disease severity index (DSI) through mycoparasitism, antibiosis, and induced systemic resistance. In aquaponic systems, the inoculation with Bacillus subtilis and Azospirillum brasilense demonstrated increased dissolved oxygen, improving water quality parameters and benefiting plant and fish growth and metabolism. This review also establishes the interaction variability between PGPM and growing media, implying the specificity for determining inoculation strategies to maximize the productivity of soilless cultivation systems. These findings suggest that using PGPM in soil-free settings could significantly contribute to sustainable crop production, addressing the challenges of nutrient management, disease control, and salinity issues.

Strain Streptomyces sp. P-56 Produces Nonactin and Possesses Insecticidal, Acaricidal, Antimicrobial and Plant Growth-Promoting Traits

Streptomycetes produce a huge variety of bioactive metabolites, including antibiotics, enzyme inhibitors, pesticides and herbicides, which offer promise for applications in agriculture as plant protection and plant growth-promoting products. The aim of this report was to characterize the biological activities of strain Streptomyces sp. P-56, previously isolated from soil as an insecticidal bacterium. The metabolic complex was obtained from liquid culture of Streptomyces sp. P-56 as dried ethanol extract (DEE) and possessed insecticidal activity against vetch aphid (Medoura viciae Buckt.), cotton aphid (Aphis gossypii Glov.), green peach aphid (Myzus persicae Sulz.), pea aphid (Acyrthosiphon pisum Harr.) and crescent-marked lily aphid (Neomyzus circumflexus Buckt.), as well as two-spotted spider mite (Tetranychus urticae). Insecticidal activity was associated with production of nonactin, which was purified and identified using HPLC-MS and crystallographic techniques. Strain Streptomyces sp. P-56 also showed antibacterial and antifungal activity against various phytopathogenic bacteria and fungi (mostly for Clavibacfer michiganense, Alternaria solani and Sclerotinia libertiana), and possessed a set of plant growth-promoting traits, such as auxin production, ACC deaminase and phosphate solubilization. The possibilities for using this strain as a biopesticide producer and/or biocontrol and a plant growth-promoting microorganism are discussed.