Plant Beneficial Microorganisms Research Articles

Crop-type-driven changes in polyphenols regulate soil nutrient availability and soil microbiota

Crop rotation is a typical agronomic practice to mitigate soil deterioration caused by continuous cropping. However, the mechanisms of soil biotic and abiotic factors in response to different cropping patterns in acidic and polyphenol-rich tea nurseries remain unclear. In this study, the composition and function of microbial communities were comparatively investigated in soils of tea seedlings continuously planted for 2 years (AC: autumn-cutting; SC: summer-cutting) and in soils rotation with strawberries alternately for 3 years (AR: autumn-cutting). The results showed that AR significantly improved the survival of tea seedlings but greatly reduced the contents of soil polyphenols. The lower soil polyphenol levels in AR were associated with the decline of nutrients (SOC, TN, Olsen-P) availability, which stimulates the proliferation of nutrient cycling-related bacteria and mixed-trophic fungi, endophytic fungi and ectomycorrhizal fungi, thus further satisfying the nutrient requirements of tea seedlings. Moreover, lower levels of polyphenols facilitated the growth of plant beneficial microorganisms (Bacillus, Mortierella, etc.) and suppressed pathogenic fungi (Pseudopestalotiopsis, etc.), creating a more balanced microbial community that is beneficial to plant health. Our study broadens the understanding of the ecological role of plant secondary metabolites and provides new insights into the sustainability of tea breeding.

Long-term effect of epigenetic modification in plant\u2013microbe interactions: modification of DNA methylation induced by plant growth-promoting bacteria mediates promotion process

BackgroundSoil microbiomes are considered a cornerstone of the next green revolution, and plant growth-promoting bacteria (PGPB) are critical for microbiome engineering. However, taking plant-beneficial microorganisms from discovery to agricultural application remains challenging, as the mechanisms underlying the interactions between beneficial strains and plants in native soils are still largely unknown. Increasing numbers of studies have indicated that strains introduced to manipulate microbiomes are usually eliminated in soils, while others have reported that application of PGPB as inocula significantly improves plant growth. This contradiction suggests the need for a deeper understanding of the mechanisms underlying microbe-induced growth promotion.ResultsWe showed PGPB-induced long-term plant growth promotion after elimination of the PGPB inoculum in soils and explored the three-way interactions among the exogenous inoculum, indigenous microbiome, and plant, which were key elements of the plant growth-promoting process. We found the rhizosphere microbiome assembly was mainly driven by plant development and root recruitments greatly attenuated the influence of inocula on the rhizosphere microbiome. Neither changes in the rhizosphere microbiome nor colonization of inocula in roots was necessary for plant growth promotion. In roots, modification of DNA methylation in response to inoculation affects gene expression related to PGPB-induced growth promotion, and disruptions of the inoculation-induced DNA methylation patterns greatly weakened the plant growth promotion. Together, our results showed PGPB-induced DNA methylation modifications in roots mediated the promotion process and these modifications remained functional after elimination of the inoculum from the microbiome.ConclusionThis study suggests a new mechanism in which PGPB affect DNA methylation in roots to promote plant growth, which provides important insights into microbiome–plant interactions and offers new strategies for plant microbiome engineering beyond the perspective of maintaining inoculum persistence in soils.4DAt-NxeARCpvmCXo93oLmVideo abstractGraphical abstract

Induced Systemic Resistance for Improving Plant Immunity by Beneficial Microbes.

Plant beneficial microorganisms improve the health and growth of the associated plants. Application of beneficial microbes triggers an enhanced resistance state, also termed as induced systemic resistance (ISR), in the host, against a broad range of pathogens. Upon the activation of ISR, plants employ long-distance systemic signaling to provide protection for distal tissue, inducing rapid and strong immune responses against pathogens invasions. The transmission of ISR signaling was commonly regarded to be a jasmonic acid- and ethylene-dependent, but salicylic acid-independent, transmission. However, in the last decade, the involvement of both salicylic acid and jasmonic acid/ethylene signaling pathways and the regulatory roles of small RNA in ISR has been updated. In this review, the plant early recognition, responsive reactions, and the related signaling transduction during the process of the plant–beneficial microbe interaction was discussed, with reflection on the crucial regulatory role of small RNAs in the beneficial microbe-mediated ISR.

THE COMPOST, A SOURCE OF PLANT BENEFICIAL BACTERIA WITH BIOCONTROL POTENTIAL

Recycling the sewage sludge from treatment plants is a common activity. The resulting compost is usually rich in plant nutrients and beneficial microorganisms. However, compost properties greatly differ depending on the nature of the fermented biomass and fermentation processes. The aim of this study was to analyze the microbial load of three different composts, in order to detect new bacterial strains with plant protection properties. Isolated bacteria were microbiologically characterized and evaluated for their potential to reduce soil-borne phytopathogenic fungi. Results showed a microbial load of approximately 106 CFU/g of compost. In the analyzed samples it was revealed that as bacterial load increases, the fungal amount decreases. Analyzing some newly isolated bacteria obtained from these composts, a good biocontrol potential against soil-borne pathogenic fungi was revealed. Some of the isolated bacterial strains revealed antifungal activity against Rhizoctonia solani and Sclerotinia sclerotiorum. These bacteria showed good colonization capacity and lytic enzymes production, correlated to antimicrobial activity. These compost-originated bacteria reveal high potential in pathogens inhibition. Therefore, the analyzed composts are recommended not only as soil fertility improvers, but also as potential suppressors of soil-borne pathogens. Results revealed these composts as source of plant beneficial bacteria with biological control potential.

Effect of Chicken Manure-Based Fertiliser on Bacterial Communities and Diversity of Tomato Endosphere Microbiota

Abstract The frequent use of chemical fertiliser produces harmful effects on the soil ecosystem. Therefore, biocompatible methods are used to improve plant health and production through natural fertiliser or plant beneficial microorganisms. This study aims to investigate the effect of amended chicken manure-based natural fertiliser on bacterial communities and plant beneficial bacteria of tomato endosphere microbiome using the high throughput 16S rRNA gene amplicon sequencing. The results showed Proteobacteria (89.4 ± 4.7% to 86.7 ± 3.9%), Actinobacteria (6.03 ± 2.9% to 3.56 ± 2.1%), and Firmicutes (3.34 ± 1.3% to 0.59 ± 0.3%) as the dominant bacterial phyla of tomato endophytic microbiome. Pseudomonas and Bacillus were the most abundant identifiable genera in the chicken manure root (CMR) (amended manure treatments) sample. There was no significant difference in alpha bacterial diversity (Shannon index: p = 0.48) and species richness (Chao 1: p = 0.43) between control original root (OR) and CMR. However, the distribution of the dominant phyla was mainly affected by manure fertilisation. The non-metric multidimensional scaling (NMDS) and PCoA of beta diversity analysis suggested a significant separation in bacterial communities of tomato endophytes between CMR and OR. The most differently abundant bacterial taxa belong to Bacteroidetes in the OR group, whereas the beneficial bacterial communities of Actinobacteria and Firmicutes were more abundant in the CMR group. Therefore, the chicken manure application can significantly affect bacterial communities of tomatoes´ root endophytic microbiome and effectively improve the abundance of the beneficial microbes as biofertilisers.

Characterization of bacterial communities isolated from municipal waste compost and screening of their plant-interactive phenotypes

Four batches of commercial compost obtained from the organic fraction of municipal solid waste were analyzed from chemical and microbiological standpoints. The working hypothesis was that, being this type of compost derived partly from plant waste, it could contain plant-growth promoting bacterial endophytes, prone to be active again upon its usual delivery as fertilizer. Culturable bacteria were isolated at different temperatures, quantified by colony morphology, identified taxonomically by 16S sequencing and screened for plant-growth promoting phenotypes including auxin and siderophore production, phosphate solubilization and peptide mineralization to ammonia. In parallel, the total community was assessed by culture independent DNA metabarcoding. The capability of plants to select, uptake and internally multiply bacteria from these compost samples was analyzed using grapevine in-vitro rooting cuttings from which acquired bacteria were reisolated, quantified and their identities determined as above. Major differences in compost bacterial composition were observed as function of the season, with the winter sample being rather distinct from the summer ones. Bacillales and Actinomycetales dominated the culturable communities while Alteromonadales, Oceanospirillales and Flavobacteriales prevailed in the total community. In spite of the challenging composting cycle conditions, the plant nature of the main input substrates appeared determinant in guaranteeing that 82% of the culturable bacteria were found endowed with one or more of the plant growth-promoting phenotypes tested. Beside its fertilization role, compost proved to be also a potential inoculant carrier for the in-soil delivery of plant beneficial microorganisms. Furthermore, upon an in vitro passage through grapevine plants under axenic conditions, the subsequently recoverable endophyte community yielded also members of the Rhizobiales order which had not been detectable when culturing directly from compost. This observation further suggests that compost-borne plant-interacting taxa could be also rescued from non-culturable states and/or enriched above detectability levels by a contact with their potential host plants.

The use of indigenous bacterial community as inoculant for plant growth promotion in soybean cultivation

ABSTRACT We characterized the bacterial community in shoot and rhizosphere of healthy adult soybean plants grown in two differentially managed soils. Then, these communities were transplanted to seeds to assess their effect on seedling development. The bacterial communities of inoculated soybean seedlings were assessed through 16S rRNA amplicon sequencing and seedlings’ growth was measured. The diversity in the bacterial consortium inoculum prepared from the rhizosphere was higher than those from the shoot. However, the application of bacterial consortium in seedling had no influence on diversity. The resulting bacterial community of seedlings inoculated with bacterial consortium presented an enrichment of specific plant growth-promoting groups, such as Gammaproteobacteria (Enterobacter, Pseudomonas, and Xanthomonas). The predicted potential functions showed an increased abundance of functions related to plant protection and nutrition. The application of bacterial consortium from the shoot of soybean plants grown in the soil with a previous history of soybean cultivation increased the seedling radicle length, hypocotyl length, and total dry weight by 44%, 30%, and 29%, respectively. Our study showed that selecting a consortium of indigenous microbes as inoculants is a potential approach to enhance the use and impacts of plant beneficial microorganisms on plant growth and possibly productivity.

Reaping the Benefits of Microorganisms in Cropping Systems: Is the Regulatory Policy Adequate?

Within food plant cropping systems, microorganisms provide vital functions and ecosystem services, such as biological pest and disease control, promotion of plant growth and crop quality, and biodegradation of organic matter and pollutants. The beneficial effects of microorganisms can be achieved and/or enhanced by agricultural management measures that target the resident microbial biodiversity or by augmentation with domesticated and propagated microbial strains. This study presents a critical review of the current legislation and regulatory policies pertaining to the utilization of plant-beneficial microorganisms in the European Union (EU). For augmentative approaches, the nature of the intended effect and the product claim determine how a microbiological product is categorized and regulated, and pre-market authorization may be mandatory. Typically, microbial products have been incorporated into frameworks that were designed for evaluating non-living substances, and are therefore not well suited to the specific properties of live microorganisms. We suggest that regulatory harmonization across the sector could stimulate technical development and facilitate implementation of crop management methods employing microorganisms. Possible scenarios for regulatory reform in the longer term are discussed, but more investigation into their feasibility is needed. The findings of this study should serve as a catalyst for more efficient future use of plant-beneficial microorganisms, to the benefit of agriculture as well as the environment.

Fermentation Strategies to Improve Soil Bio-Inoculant Production and Quality.

The application of plant beneficial microorganisms has been widely accepted as an efficient alternative to chemical fertilizers and pesticides. Isolation and selection of efficient microorganisms, their characterization and testing in soil-plant systems are well studied. However, the production stage and formulation of the final products are not in the focus of the research, which affects the achievement of stable and consistent results in the field. Recent analysis of the field of plant beneficial microorganisms suggests a more integrated view on soil inoculants with a special emphasis on the inoculant production process, including fermentation, formulation, processes, and additives. This mini-review describes the different groups of fermentation processes and their characteristics, bearing in mind different factors, both nutritional and operational, which affect the biomass/spores yield and microbial metabolite activity. The characteristics of the final products of fermentation process optimization strategies determine further steps of development of the microbial inoculants. Submerged liquid and solid-state fermentation processes, fed-batch operations, immobilized cell systems, and production of arbuscular mycorrhiza are presented and their advantages and disadvantages are discussed. Recommendations for further development of the fermentation strategies for biofertilizer production are also considered.

‘The Good, the Bad and the Ugly’ in the shades of green: the genus Trichoderma in the spotlight

The ascomycetous filamentous fungal genus Trichoderma has at least two faces, like Agni, the God of fire in Hindu mythology. Or maybe even three? The ‘Good’, the ‘Bad’ and the ‘Ugly’? In fact, Trichoderma species can be considered: (1) ‘Good’—as plant-beneficial microorganisms in agriculture due to a plethora of antagonistic mechanisms acting against plant pathogens, e.g., inhibiting them through the production of antimicrobial metabolites or by direct parasitism, or indirectly, promoting the growth of crop plants and inducing their immune system; (2) ‘Bad’ —as devastating agents of green mould diseases in the cultivation of mushrooms viz. champignon, oyster mushroom, shiitake, etc., destroying crops and thereby causing serious economic damage world-wide; and (3) ‘Ugly’—as opportunistic pathogens of mainly immunocompromised humans. Do biocontrol Trichoderma strains represent a risk to mushroom production or human health? Is the agricultural application of Trichoderma strains safe or rather risky? The aim of this review is to address these important questions.

Protists as main indicators and determinants of plant performance

BackgroundMicrobiomes play vital roles in plant health and performance, and the development of plant beneficial microbiomes can be steered by organic fertilizer inputs. Especially well-studied are fertilizer-induced changes on bacteria and fungi and how changes in these groups alter plant performance. However, impacts on protist communities, including their trophic interactions within the microbiome and consequences on plant performance remain largely unknown. Here, we tracked the entire microbiome, including bacteria, fungi, and protists, over six growing seasons of cucumber under different fertilization regimes (conventional, organic, and Trichoderma bio-organic fertilization) and linked microbial data to plant yield to identify plant growth-promoting microbes.ResultsYields were higher in the (bio-)organic fertilization treatments. Soil abiotic conditions were altered by the fertilization regime, with the prominent effects coming from the (bio-)organic fertilization treatments. Those treatments also led to the pronounced shifts in protistan communities, especially microbivorous cercozoan protists. We found positive correlations of these protists with plant yield and the density of potentially plant-beneficial microorganisms. We further explored the mechanistic ramifications of these relationships via greenhouse experiments, showing that cercozoan protists can positively impact plant growth, potentially via interactions with plant-beneficial microorganisms including Trichoderma, the biological agent delivered by the bio-fertilizer.ConclusionsWe show that protists may play central roles in stimulating plant performance through microbiome interactions. Future agricultural practices might aim to specifically enhance plant beneficial protists or apply those protists as novel, sustainable biofertilizers.9YGnSNgqaHj2gH_1N6en5wVideo abstract

Localization and survival of Azospirillum brasilense Az39 in soybean leaves.

In recent years, foliar inoculation has gained acceptance among the available methods to deliver plant beneficial micro-organisms to crops under field conditions. Colonization efficiency by such micro-organisms largely depends on their ability to survive when applied on the leaves. In this work, we evaluated the survival and localization of Azospirillum brasilense Az39 (Az39) in excised soybean leaves. Scanning electron microscopy and confocal laser scanning microscopy of a red fluorescent-transformed variant of Az39 were used to determine bacterial localization, while the most probable number and plate count methods were applied for bacterial quantification. Microscopic observations indicated a decrease in the number of Az39 cells on the leaf surface at 24h after treatment, whereas midribs and cell-cell junctions of the inner leaf epidermis became highly populated zones. The presence of Az39 inside xylem vessels was corroborated at 6h after bacterization. Az39 population did not significantly decrease throughout 24h. We could visualize Az39 cells on the surface and in internal tissues of soybean leaves and recover them through culture methodologies. These results evidence the survival capacity of Az39 on and inside leaves and suggest a previously unnoticed endophytic potential for this well-known plant growth-promoting rhizobacteria strain.

The Conception of Microbial Preparations Development for a Crop Production

As a result of the analysis of scientific literature data and based on our experimental data, we present the conception of mutual relations between beneficial microorganisms and plants in the soil: a) for the purposeful management of processes in agro- and natural phytocenoses it is necessary to consider all components of the plant-microbial community (plant, arbuscular mycorrhizas, nodule bacteria and all microorganisms stimulating plants growth and development, both endophytic and epiphytic), as a uniform gen-metabolic net; b) it is necessary to consider, that the rate of microsymbionts genomes evolution exceeds the rate of plant evolution and consequently the plant should be considered as the most genetically stable in time, key component controlling the efficiency of plant-microbial systems functioning. According to the basic conception of intensive agriculture within several decades all over the world, the selection of new breeds of agricultural plants was conducted on a high agrotechnical level with the application of high doses of fertilizers and chemicals. The attention was paid only to the negative influence of a pathogenic microbiota on plants and according to this, the resistance of plants to such conditions. As a rare example, in the case of legumes farmers took into account the symbiotic nitrogen fixation that is mutualistic interactions of plants with nodule bacteria. It is necessary to notice, that the genetic systems of legumes controlled the interaction with nodule bacteria, arbuscular mycorrhiza and plant growth promoting bacteria (PGPB), have a series of common genes. It should be considered as a uniform polygene net and to be the object of selection on integral feature “efficiency of interaction with microorganisms beneficial to plants”, instead on separate signs characterizing the efficiency of formation of separate types of mutually advantageous plant-microbial symbioses; c) at the beginning of plant selection history, not having the effective technologies and knowledge about the structure of plant genetic system, monitoring mutual relations of plants with microorganisms, scientists breeders intuitively followed the laws dictated by natureconducted selection against an undisturbed structure of plant beneficial microorganisms community on the integral feature of plant productivity. Today it is necessary to return to the initial practice of selection, but with the account of effective technologies and new knowledge of plant-microbial interactions and to make plant selection to increase the symbiotic potential of such interaction against its maximum genetic diversity. It is reasonable to conduct plant selection on such features as additional biomass, saved up by the formation of the mutualistic plant-microbial system and quality of received production. Due to such selection, the commercial breeds of agricultural plants maximum efficiently operating the interaction with microorganisms in agrophytocenosis will be received. As a result of applying this conception, the technologies for production of complex microbial preparations BIST, Pseudorizobin and Zamin were developed, patented and successfully tested in the Republic of Uzbekistan.

Application of Encapsulated Bacillus licheniformis Supplemented with Chitosan Nanoparticles and Rice Starch for the Control of Sclerotium rolfsii in Capsicum annuum (L.) Seedlings.

Rhizosphere encourages the survival and functioning of diverse microbial communities through the influence of plant roots. Likewise, the rhizobacterial functioning contribute to the growth and productivity of crop plants significantly. With the advancement of nanotechnology, the nanoparticles can expect to augment the performance of plant beneficial microorganisms including the rhizobacteria and hence have the promise to boost sustainable agricultural practices. In the present study, Bacillus licheniformis encapsulated in alginate-chitosan nanoparticles (CNPs) beads supplemented with rice starch (RS) has been evaluated for its plant growth enhancement and disease control properties. The encapsulated Bacillus licheniformis was initially characterized for indole-3-acetic acid (IAA) production, nitrogen fixing capacity, 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase production and antifungal activity against Sclerotium rolfsii. In addition to this, the plant growth promoting and biocontrol properties of the encapsulated Bacillus licheniformis were also evaluated using Capsicum annuum (L.)(chilli) seedlings. From the results, the plants treated with encapsulated Bacillus licheniformis supplemented with CNPs were found to have maximum growth enhancement. At the same time, plants treated with encapsulated Bacillus licheniformis supplemented with CNPs and RS were found to have enhanced disease suppression. This revealed the application of encapsulated Bacillus licheniformis supplemented with CNPs and RS as a promising delivery system for agricultural applications.

"PLANT-BENEFICIAL MICROBIAL INOCULANTS AND THEIR FORMULATION – A REVIEW"

" Agriculture plays a crucial role in the society and global economy and has a huge impact on the environment. Human overpopulation require higher amounts of food, and due to the overwhelming increase of health disorder it is a consumer demand for high quality food products. However, intensive agricultural practices involve the use of synthetic substances, with negative effects on human health and environmental safety. These triggered the concern of global regulatory agencies for new strategies and harsh regulations regarding agricultural inputs. Sustainable agriculture practices, including the use of renewable resources are now promoted. Biofertilizers, biopesticides and biostimulants contribute to agricultural yield and quality improvement, having a low detrimental impact on the environment. Microbial inoculants based on selected microorganisms are promising products that can improve plant growth and productivity and prevent crops from pest and diseases attack, being an environmental friendly approach. Plant beneficial microorganisms trigger various mechanisms for soil improvement, nitrogen fixation, nutrients solubilization and uptake in plants. Some beneficial microorganisms can release active biomolecule involved in plant protection, or suppress biotic and abiotic stress factors, revealing plant or environmental benefits. This study aims to review plant beneficial microbial agro-inoculants, successful formulations and application methods."

Minimizing abrasion losses from film-coated corn seeds

ABSTRACT Film-coating is a widely used technology to apply plant protection agents, beneficial microorganisms, and other substances to seeds. During handling and planting operations, fragments of the seed coat can become detached by mechanical abrasion and are released into the environment. Modest reductions in abrasion losses have been achieved by selecting polymers and formulations with improved adherence to seed surfaces. The objective of this study was to investigate a novel approach for reducing abrasion risk with film-coated corn (Zea mays L.) seeds and to evaluate an improved image-based protocol for rapid and effective evaluation of seed abrasion. This study demonstrated that the risk of abrasion losses from film-coated corn seeds was minimized by removing the outer wax layer of the seed pericarp prior to applying coat formulations. Removal of the outer wax layer did not affect seed germination or seedling growth, but it did improve the adhesion strength of the coat to the seed surface and effectively reduced abrasion losses. Coating surface of dewaxed seeds with three different treatment formulations, viz., a commercial seed-coating polymer, a starch-based bioplastic and a soy protein isolate-based preparation, reduced fragment release by 97.6%, 94.8%, and 98.9%, respectively, with respect to non-surface dewaxed seeds. Seed coatings placed in soil for six days deteriorated 2.5% and 72.1% for commercial and bioplastic formulations, respectively, whereas the soy protein isolate coating formulation deteriorated almost completely under the same conditions. Thus, removing the outer wax layer before film-coating seeds and using novel seed coat formulations improved environmental profile of coated seeds.

Effects of Rhizobium Inoculation on N2 Fixation, Phytochemical Profiles and Rhizosphere Soil Microbes of Cancer Bush Lessertia frutescens (L.)

Plant-beneficial microorganisms are determinants of plant health and productivity. However, the effects associated with secondary plant metabolism and interactions in the rhizosphere for Cancer bush Lessertia frutescens (L.) is unclear. The study was conducted to understand the mechanism of rhizobium inoculation for L. frutescens, variations in phytochemicals, soluble sugars, and soil–plant interactions in the rhizosphere. Four rhizobium inoculation levels (0, 100, 200, and 400 g) were evaluated under the field conditions to establish the antioxidant properties, soluble sugars, and rhizosphere soil microbial diversity at 150, 240, and 330 days after planting (d.a.p). Although inoculation did not significantly affect plant biomass and N2 fixation of L. frutescens, total phenolics and flavonoids were enhanced with the application of 200 g at 240 days after planting. The antioxidant values analyzed through FRAP (Ferric reducing power assay) were highest with 100 g inoculation at 240 days after planting. Water-soluble sugars such as fructose, sucrose, and glucose increased with the application of 400, 200, and 100 g rhizobium inoculation. The rhizosphere′s carbon source utilization profiles (CSUP) did not vary significantly, depicting the weaker ability in converting C, P, and N profiles. The lowest ß glucosidase activity was observed in the bulk soil with the lowest alkaline and acid phosphatase activities. Soil microbial populations present in the bulk sample demonstrated the smallest overall enzyme activities. The variation of different variables studied indicate the potential of rhizobium inoculation. However, further studies are required to ascertain the inoculation′s effectiveness for plant growth and rhizosphere microbial populations of L. frutescens.

The Importance of Microbial Inoculants in a Climate-Changing Agriculture in Eastern Mediterranean Region

Climate change has gained importance due to its severe consequences for many aspects of life. Increasing temperature, drought and greenhouse gases affect directly or indirectly the productivity of agricultural and natural ecosystems as well as human health. The nutrient supply capacity of the soil is diminishing, while food requirements for the growing population are increasing. The ongoing application of agrochemicals results in adverse effects on ecosystem functioning and food chain. Now, more than ever, there is a need to mitigate the effects of agricultural activities on climate change using environmentally friendly techniques. The role of plant beneficial microorganisms on this global challenge is increasingly being explored, and there is strong evidence that could be important. The use of functional microbial guilds forms an alternative or even a supplementary approach to common agricultural practices, due to their ability to act as biofertilizers and promote plant growth. Application of microbial inocula has a significantly lower impact on the environment compared to chemical inputs, while the agricultural sector will financially benefit, and consumers will have access to quality products. Microbial inoculants could play an important role in agricultural stress management and ameliorate the negative impacts of climate change. This short review highlights the role of microbes in benefiting agricultural practices against climate-changing conditions. In particular, the main microbial plant growth-promoting functional traits that are related to climate change are presented and discussed. The importance of microbial inoculants’ multifunctionality is debated, while future needs and challenges are also highlighted.

Prospective evaluation of individual and consortia plant growth promoting rhizobacteria for drought stress amelioration in rice (Oryza sativa L.)

Rice (Oryza sativa L.) being the most important crop for human population in Asia region, accounts for 23% of the world’s caloric intake. Due to the changing climatic conditions, the agricultural crops are experiencing vagaries of the weather more frequently leading to yield losses and even crop failure. The objective of this study was to find out a suitable consortium of bacterial inoculants which can make the crop resilient to drought stress. Bacterial isolates from different habitats were characterized for salt tolerance and multiple plant growth promoting traits. Four separate treatments were formulated, with two treatments having individual bacterial strain as PGPR and the rest two having consortia of three bacterial isolates as PGPR. High yielding variety MTU1010 was selected for pot experiments and treated with individual as well as consortium of isolates. Drought was imposed for 10 days to different batch of the rice crop (variety MTU1010) at two stages of crop growth i.e., pre-flowering and flowering stages. Results indicated amelioration of drought stress with higher biomass accumulation, increased grain yield and reversal of stress indicators in plants inoculated with PGPR. The antioxidant enzyme activity of SOD, CAT, and GPOX declined by 24%, 20.5% and 20% in plants treated with bacterial inoculum as compared to un-inoculated control. This study indicates that the plant beneficial microorganisms can be used to induce systematic tolerance to rice plants under drought stress and furthermore, application of consortium of PGPR has better probability to improve the coping capacity of the plants exposed to stress conditions.

Responses of active soil microorganisms facing to a soil biostimulant input compared to plant legacy effects

Agriculture is changing to rely on agroecological practices that take into account biodiversity, and the ecological processes occurring in soils. The use of agricultural biostimulants has emerged as a valid alternative to chemicals to indirectly sustain plant growth and productivity. Certain BS have been shown to select and stimulate plant beneficial soil microorganisms. However, there is a lack of knowledge on the effects and way of action of the biostimulants operating on soil functioning as well as on the extent and dynamic of these effects. In this study we aimed to decipher the way of action of a seaweed and amino-acids based biostimulant intended to be applied on soil crop residues to increase their microbial mineralization and the further release of nutrients. By setting-up a two-phase experiment (soil plant-growing and soil incubation), our objectives were to (1) determine the effects of the soil biostimulant over time on the active soil bacteria and fungi and the consequences on the organic carbon mineralization in bare soils, and (2) assess the biostimulant effects on soil microorganisms relatively to plant legacy effects in planted soils. We demonstrated that the soil biostimulant had a delayed effect on the active soil microorganisms and activated both plant growth promoting bacteria and saprophytes microorganisms at the medium-term of 49 days. However, the changes in the abundances of active microbial decomposers were not associated to a higher mineralization rate of organic carbon derived from soil and/or litter. The present study assessed the biostimulant beneficial effect on active soil microbial communities as similar as or even higher than the legacy effects of either A. thaliana or T. aestivum plants. We specifically showed that the biostimulant increased the active fungal richness to a higher extent than observed in soils that previously grew the two plants tested.