Unveiling the multifaceted potential of Pseudomonas khavaziana strain SR9: a promising biocontrol agent for wheat crown rot

Fusarium pseudograminearum, a soil-borne fungus, is the cause of the devastating wheat disease known as wheat crown rot (WCR). The persistence of this pathogen in the soil and crop residues contributes to the increased occurrence and severity of WCR. Therefore, developing effective strategies to prevent and manage WCR is of great importance. In this study, we isolated a bacterial strain, designated as SR9, from the stem of wheat, that exhibited potent antagonistic effects against F. pseudograminearum, as well as the biocontrol efficacy of SR9 on WCR was quantified at 83.99% ± 0.11%. We identified SR9 as Pseudomonas khavaziana and demonstrated its potential as a plant probiotic. SR9 displayed broad-spectrum antagonism against other fungal pathogens, including Neurospora dictyophora, Botrytis californica, and Botryosphaeria dothidea. Whole-genome sequencing analysis revealed that SR9 harbored genes encoding various cell wall-degrading enzymes, cellulases, and lipases, along with antifungal metabolites, which are responsible for its antagonistic activity. Gene knockout and quantitative PCR analyses reveal that phenazine is the essential factor for antagonism. SR9 possessed genes related to auxin synthesis, flagellar biosynthesis, biofilm adhesion, and the chemotaxis system, which play pivotal roles in plant colonization and growth promotion; we also evaluated the effects of SR9 on plant growth in wheat and Arabidopsis. Our findings strongly suggest that SR9 holds great promise as a biocontrol agent for WCR in sustainable agriculture.IMPORTANCEThe escalating prevalence of wheat crown rot, primarily attributed to Fusarium pseudograminearum, necessitates the development of cost-effective and eco-friendly biocontrol strategies. While plant endophytes are recognized for their biocontrol potential, reports on effective strains targeting wheat crown rot are sparse. This study introduces the Pseudomonas khavaziana SR9 strain as an efficacious antagonist to the wheat crown rot pathogen Fusarium pseudograminearum. Demonstrating a significant reduction in wheat crown rot incidence and notable plant growth promotion, SR9 emerges as a key contributor to plant health and agricultural sustainability. Our study outlines a biological approach to tackle wheat crown rot, establishing a groundwork for innovative sustainable agricultural practices.

Tracking maize colonization and growth promotion by Azospirillum reveals strain-specific behavior and the influence of inoculation method

Inoculation of Azospirillum in maize has become a standard practice in Latin America. However, information on the behavior and population survival of the Azospirillum post-inoculation is scarce, making standardization difficult and generating variations in inoculation efficiency across assays. In this study, we tracked the colonization of three agriculturally relevant Azospirillum strains (Ab-V5, Az39, and the ammonium excreting HM053) after different inoculation methods in maize crops by qPCR. Besides, we assessed their ability to promote maize growth by measuring biometric parameters after conducting a greenhouse essay over 42 days. Inoculated plants exhibited Azospirillum population ranging from 103 to 107 cells plant-1 throughout the experiment. While all strains efficiently colonized roots, only A. argentinense Az39 demonstrated bidirectional translocation between roots and shoots, which characterizes a systemic behavior. Optimal inoculation methods for plant growth promotion varied among strains: soil inoculation promoted the best maize growth for the Ab-V5 and Az39 strains, while seed inoculation proved most effective for HM053. The findings of this study demonstrate that the inoculation method affects the behavior of Azospirillum strains and their effectiveness in promoting maize growth, thereby guiding practices to enhance crop yield.

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

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

Insight into farming native microbiome by bioinoculant in soil-plant system

Applying beneficial microorganisms (BM) as bioinoculants presents a promising soil-amendment strategy while impacting the native microbiome, which jointly alters soil-plant performance. Leveraging the untapped potential of native microbiomes alongside bioinoculants may enable farmers to sustainably regulate soil-plant systems via natural bioresources. This review synthesizes literature on native microbiome responses to BMs and their interactive effects on soil and plant performance. We highlight that native microbiomes harbor both microbial "helpers" that can improve soil fertility and plant productivity, as well as "inhibitors" that hinder these benefits. To harness the full potential of resident microbiome, it is crucial to elucidate their intricate synergistic and antagonistic interplays with introduced BMs and clarify the conditions that facilitate durable BM-microbiome synergies. Hence, we indicate current challenges in predicting these complex microbial interactions and propose corresponding strategies for microbiome breeding via BM bioinoculant. Overall, fully realizing the potential of BMs requires clarifying their interactions with native soil microbiomes and judiciously engineering microbiome to harness helpful microbes already present within agroecosystems.

Impact of Sodium Alginate-Encapsulated Iron Nanoparticles and Soil Yeasts on the Photosynthesis Performance of Lactuca sativa L. Plants

In a scenario of accelerated global climate change, the continuous growth of the world population, and the excessive use of chemical fertiliser, the search for sustainable alternatives for agricultural production is crucial. The present study was conducted to evaluate the plant growth-promoting (PGP) characteristics of two yeast strains, Candida guilliermondii and Rhodotorula mucilaginosa, and the physicochemical characteristics of nanometric capsules and iron oxide nanoparticles (Fe2O3-NPs) for the formulation of nanobiofertilisers. The physiological and productive effects were evaluated in a greenhouse assay using lettuce plants. The results showed that C. guilliermondii exhibited higher tricalcium phosphate solubilisation capacity, and R. mucilaginosa had a greater indole-3-acetic acid (IAA) content. The encapsulation of C. guilliermondii in sodium alginate capsules significantly improved the growth, stomatal conductance, and photosynthetic rate of the lettuce plants. Physicochemical characterisation of the Fe2O3-NPs revealed a particle size of 304.1 nm and a negative Z-potential, which indicated their stability and suitability for agricultural applications. The incorporation of Fe2O3-NPs into the capsules was confirmed by SEM-EDX analysis, which showed the presence of Fe as the main element. In summary, this study highlights the potential of nanobiofertilisers containing yeast strains encapsulated in sodium alginate with Fe2O3-NPs to improve plant growth and photosynthetic efficiency as a path toward more sustainable agriculture.

The Role of PGPB-Microalgae interaction in Alleviating Salt Stress in Plants

Plant development and yield are severely hampered by climate change. Plants are very prone to a variety of abiotic stressors during growth, making them susceptible to destruction which can reduce the productivity by 20-60%. These stresses generate reactive oxygen species (ROS), which damage lipids, proteins, and nucleic acids. Microalgae and plant growth-promoting bacteria (PGPB) are remarkably effective at reducing the effects of salt stress and promoting plant growth, thereby increasing agricultural yield, and helping ensure global food security. Through a variety of mechanisms, including the production of phytohormones, 1-aminocyclopropane-1-carboxylic acid deaminase, exopolysaccharide, siderophores, hydrogen cyanide, extracellular polymeric substances, volatile organic compounds, and modulation of antioxidants defense machinery under abiotic stresses promote plant growth after inoculation of PGPB and microalgae. These microorganisms also maintain ion homeostasis, offer osmotic balance, stimulate genes that respond to salt and drought, rewire the metabolism, modify the transcription of ion transporter genes, and more. To counteract the negative consequences of salinity stress, this study summarizes the effects of PGPB- microalgae along with a tentative protective mechanism during salinity stress for sustainable agriculture.

Exploring the therapeutic potential of the oxygenated monoterpene linalool in alleviating saline stress effects on Allium cepa L

Sodium chloride (NaCl) can cause oxidative stress in plants, which represents a potential obstacle to the development of monocultures worldwide. Onion (Allium cepa L.) is a famous vegetable consumed and used in world cuisine. In the present study, we analyzed the influence of soil physicochemical profile and the remedial capacity of linalool on seed emergence, roots, and leaf growth in onions subjected to salt stress, as well as its in vivo and in vitro antioxidant potential, Fe2+chelating activity, and reducing power of Fe3+. The outcome of the soil analysis established the following order of abundance: sulfur (S) > calcium (Ca) > potassium (K) > magnesium (Mg) > sodium (Na). NaCl (150 mM) significantly reduced the emergence speed index (ESI), leaf and root length, while increasing the peroxidation content. The length of leaves and roots significantly increased after treatment with linalool (300 and 500 μg/mL). Our data showed negative correlations between seed emergence and K+ concentration, which was reversed after treatments. Linalool (500 μg/mL) significantly reduced oxidative stress, but increased Fe2+ concentration and did not show potential to reduce Fe3+. The in vivo antioxidant effect of linalool is thought to primarily result from an enzymatic activation process. This mechanism underscores its potential as a therapeutic agent for oxidative stress-related conditions. Further investigation into this process could unveil new avenues for antioxidant therapy.

Limited efficacy of a commercial microbial inoculant for improving growth and physiological performance of native plant species

Soil microbial inoculants are increasingly being explored as means to improve soil conditions to facilitate ecological restoration. In southwestern Western Australia, highly biodiverse Banksia woodland plant communities are increasingly threatened by various factors including climate change, land development and mining. Banksia woodland restoration is necessary to conserve this plant community. The use of microbial inoculation in Banksia woodland restoration has not yet been investigated. Here, we evaluated the efficacy of a commercial microbial inoculant (GOGO Juice, Neutrog Australia Pty Ltd) for improving the performance of 10 ecologically diverse Banksia woodland plant species in a pot experiment. Plants were subjected to one of two watering regimes (well-watered and drought) in combination with microbial inoculation treatments (non-inoculated and inoculated). Plants were maintained under these two watering treatments for 10 weeks, at which point plants in all treatments were subjected to a final drought period lasting 8 weeks. Plant performance was evaluated by plant biomass and allocation, gas exchange parameters, foliar carbon and nitrogen and stable isotope (δ15N and δ13C) compositions. Plant xylem sap phytohormones were analysed to investigate the effect of microbial inoculation on plant phytohormone profiles and potential relationships with other observed physiological parameters. Across all investigated plant species, inoculation treatments had small effects on plant growth. Further analysis within each species revealed that inoculation treatments did not result in significant biomass gain under well-watered or drought-stressed conditions, and effects on nitrogen nutrition and photosynthesis were variable and minimal. This suggests that the selected commercial microbial inoculant had limited benefits for the tested plant species. Further investigations on the compatibility between the microorganisms (present in the inoculant) and plants, timing of inoculation, viability of the microorganisms and concentration(s) required to achieve effectiveness, under controlled conditions, and field trials are required to test the feasibility and efficacy in actual restoration environments.

A meta-analysis on crop growth and heavy metals accumulation with PGPB inoculation in contaminated soils

Plant growth-promoting bacteria (PGPB) offer a promising solution for mitigating heavy metals (HMs) stress in crops, yet the mechanisms underlying the way they operate in the soil-plant system are not fully understood. We therefore conducted a meta-analysis with 2037 observations to quantitatively evaluate the effects and determinants of PGPB inoculation on crop growth and HMs accumulation in contaminated soils. We found that inoculation increased shoot and root biomass of all five crops (rice, maize, wheat, soybean, and sorghum) and decreased metal accumulation in rice and wheat shoots together with wheat roots. Key factors driving inoculation efficiency included soil organic matter (SOM) and the addition of exogenous fertilizers (N, P, and K). The phylum Proteobacteria was identified as the keystone taxa in effectively alleviating HMs stress in crops. More antioxidant enzyme activity, photosynthetic pigment, and nutrient absorption were induced by it. Overall, using PGPB inoculation improved the growth performance of all five crops, significantly increasing crop biomass in shoots, roots, and grains by 33 %, 35 %, and 20 %, respectively, while concurrently significantly decreasing heavy metal accumulation by 16 %, 9 %, and 37 %, respectively. These results are vital to grasping the benefits of PGPB and its future application in enhancing crop resistance to HMs.

Performance of Halo-Alkali-Tolerant Endophytic Bacteria on Hybrid Pennisetum and Bacterial Community under Varying Soil Conditions

Halo-alkali soil threatens agriculture, reducing growth and crop yield worldwide. In this study, physicochemical and molecular techniques were employed to explore the potential of halo-alkali-tolerant endophytic bacteria strains Sphingomonas sp. pp01, Bacillus sp. pp02, Pantoea sp. pp04, and Enterobacter sp. pp06 to enhance the growth of hybrid Pennisetum under varying saline conditions. The strains exhibited tolerance to high salt concentrations, alkaline pH, and high temperatures. Under controlled conditions, all four strains showed significant growth-promoting effects on hybrid Pennisetum inoculated individually or in combination. However, the effects were significantly reduced in coastal saline soil. The best growth-promoting effect was achieved under greenhouse conditions, increasing shoot fresh and dry weights of hybrid Pennisetum by up to 457.7% and 374.7%, respectively, using irrigating trials. Metagenomic sequencing analysis revealed that the diversity and composition of rhizosphere microbiota underwent significant changes after inoculation with endophytic bacteria. Specifically, pp02 and co-inoculation significantly increased the Dyella and Pseudomonas population. Firmicutes, Mycobacteria, and Proteobacteria phyla were enriched in Bacillus PP02 samples. These may explain the best growth-promoting effects of pp02 and co-inoculation on hybrid Pennisetum under greenhouse conditions. Our findings reveal the performance of endophytic bacterial inoculants in enhancing beneficial microbiota, salt stress tolerance, and hybrid Pennisetum growth.

Enhanced wheat productivity in saline soil through the combined application of poultry manure and beneficial microbes

BACKGROUND

Soil salinity is one of the major menaces to food security, particularly in dealing with the food demand of the ever-increasing global population. Production of cereal crops such as wheat is severely affected by soil salinity and improper fertilization. The present study aimed to examine the effect of selected microbes and poultry manure (PM) on seedling emergence, physiology, nutrient uptake, and growth of wheat in saline soil. A pot experiment was carried out in research area of Institute of Soil and Environmental Sciences, University of Agriculture, Faisalabad, Pakistan. Saline soil (12 dS m- 1 w/w) was developed by spiking using sodium chloride, and used in experiment along with two microbial strains (i.e., Alcaligenes faecalis MH-2 and Achromobacter denitrificans MH-6) and PM. Finally, wheat seeds (variety Akbar-2019) were sown in amended and unamended soil, and pots were placed following a completely randomized design. The wheat crop was harvested after 140 days of sowing.

RESULTS

The results showed a 10-39% increase (compared to non-saline control) in agronomic, physiological, and nutritive attributes of wheat plants when augmented with PM and microbes. Microbes together with PM significantly enhanced seedling emergence (up to 38%), agronomic (up to 36%), and physiological (up to 33%) in saline soil as compared to their respective unamended control. Moreover, the co-use of microbes and PM also improved soil's physicochemical attributes and enhanced N (i.e., 21.7%-17.1%), P (i.e., 24.1-29.3%), and K (i.e., 28.7%-25.3%) availability to the plant (roots and shoots, respectively). Similarly, the co-use of amendments also lowered the Na+ contents in soil (i.e., up to 62%) as compared to unamended saline control. This is the first study reporting the effects of the co-addition of newly identified salt-tolerant bacterial strains and PM on seedling emergence, physiology, nutrient uptake, and growth of wheat in highly saline soil.

CONCLUSION

Our findings suggest that co-using a multi-trait bacterial culture and PM could be an appropriate option for sustainable crop production in salt-affected soil.

Trichoderma guizhouense NJAU4742 augments morphophysiological responses, nutrient availability and photosynthetic efficacy of ornamental Ilex verticillata

Winterberry holly (Ilex verticillata [L.] A. Gray), a deciduous shrub producing glossy bright red berries, is a valuable ornamental and medicinal plant with good market prospects. However, the growth and development of I. verticillata are significantly affected by various stresses, and environmentally hazardous agrochemicals are often used to mitigate them. Trichoderma spp., ubiquitous soil-borne eco-friendly plant growth-promoting fungi, are potent biostimulants and biofertilizers and viable alternatives to agrochemicals for healthy and sustainable agriculture. In this study, the temporal efficacy of different dosages of the filamentous fungus Trichoderma guizhouense NJAU4742 in promoting morphophysiological responses of I. verticillata and the physicochemical properties and enzymatic activities of the substrate were investigated. Different concentrations of the strain T. guizhouense NJAU4742 spore suspension (C [0%], T1 [5%, v/m], T2 [10%, v/m] and T3 [15%, v/m]) were injected in the substrate contained in a pot in which 1-year-old I. verticillata was planted for temporal treatment (15, 45 and 75 days) under open-air conditions. The beneficial effects of T2 and/or T3 treatment for a long duration (75 days) were evident on the different root, aerial and photosynthetic traits; total contents of nitrogen (N), phosphorus (P) and potassium (K) in different tissues and the physicochemical properties of the substrate and its enzymatic activities (urease and invertase). Overall, the study revealed the potency of strain T. guizhouense NJAU4742 as a sustainable solution to improve the growth and development and ornamental value of I. verticillata.

The AT-hook protein AHL29 promotes Bacillus subtilis colonization by suppressing SWEET2-mediated sugar retrieval in Arabidopsis roots

Beneficial Bacillus subtilis (BS) symbiosis could combat root pathogenesis, but it relies on root-secreted sugars. Understanding the molecular control of sugar flux during colonization would benefit biocontrol applications. The SWEET (Sugar Will Eventually Be Exported Transporter) uniporter regulates microbe-induced sugar secretion from roots; thus, its homologs may modulate sugar distribution upon BS colonization. Quantitative polymerase chain reaction revealed that gene transcripts of SWEET2, but not SWEET16 and 17, were significantly induced in seedling roots after 12 h of BS inoculation. Particularly, SWEET2-β-glucuronidase fusion proteins accumulated in the apical mature zone where BS abundantly colonized. Yet, enhanced BS colonization in sweet2 mutant roots suggested a specific role for SWEET2 to constrain BS propagation, probably by limiting hexose secretion. By employing yeast one-hybrid screening and ectopic expression in Arabidopsis protoplasts, the transcription factor AHL29 was identified to function as a repressor of SWEET2 expression through the AT-hook motif. Repression occurred despite immunity signals. Additionally, enhanced SWEET2 expression and reduced colonies were specifically detected in roots of BS-colonized ahl29 mutant. Taken together, we propose that BS colonization may activate repression of AHL29 on SWEET2 transcription that would be enhanced by immunity signals, thereby maintaining adequate sugar secretion for a beneficial Bacillus association.

Multifarious plant growth-promoting traits of mangrove yeasts: growth enhancement in mangrove seedlings (Rhizophora mucronata) for conservation

Plant Growth-Promoting Yeasts (PGPY) have garnered significant attention in recent years; however, research on PGPY from mangroves remains a largely unexplored frontier. This study, therefore, focused on exploring the multifaceted plant growth-promoting (PGP) capabilities of yeasts isolated from mangroves of Puthuvype and Kumbalam. The present work found that manglicolous yeasts exhibited diverse hydrolytic properties, with the predominance of lipolytic activity, in addition to other traits such as phosphate solubilization, and production of indole acetic acid, siderophore, ammonia, catalase, nitrate, and hydrogen cyanide. After screening for 15 PGP traits, three strains P 9, PV 23, and KV 35 were selected as the most potent ones. These strains also exhibited antagonistic activity against fungal phytopathogens and demonstrated resilience to abiotic stresses, making them not only promising biocontrol agents but also suited for field application. The potent strains P 9, PV 23, and KV 35 were molecularly identified as Candida tropicalis, Debaryomyces hansenii, and Aureobasidium melanogenum, respectively. The potential of these strains in enhancing the growth performance of mangrove seedlings of Rhizophora mucronata, was demonstrated using the pot-experiment. The results suggested that the consortium of three potent strains (P 9, PV 23, and KV 35) was more effective in increasing the number of shoot branches (89.2%), plant weight (87.5%), root length (83.3%), shoot height (57.9%) and total leaf area (35.1%) than the control seedlings. The findings of this study underscore the significant potential of manglicolous yeasts in contributing to mangrove conservation and restoration efforts, offering a comprehensive understanding of their diverse plant growth-promoting mechanisms and highlighting their valuable role in sustainable ecosystem management.

Microbial consortia and biochar as sustainable biofertilisers: Analysis of their impact on wheat growth and production

The European Union is among the top wheat producers in the world, but its productivity relies on adequate soil fertilisation. Biofertilisers, either alone or in combination with biochar, can be a preferable alternative to chemical fertilisers. However, the addition of biofertilisers, specifically plant growth promoting microbes (PGPM), could modify grain composition, and/or deteriorate the soil composition. In this study, the two wheat cultivars Triticum aestivum (Bramante) and T. durum (Svevo) were cultivated in open fields for two consecutive years in the presence of a commercial PGPM mix supplied alone or in combination with biochar. An in-depth analysis was conducted by collecting physiological and agronomic data throughout the growth period. The effects of PGPM and biochar were investigated in detail; specifically, soil chemistry and rhizosphere microbial composition were characterized, along with the treatment effects on seed storage proteins. The results demonstrated that the addition of commercial microbial consortia and biochar, alone or in combination, did not modify the rhizospheric microbial community; however, it increased grain yield, especially in the cultivar Svevo (increase of 6.8 %-13.6 %), even though the factors driving the most variations were associated with both climate and cultivar. The total gluten content of the flours was not affected, whereas the main effect of the treatments was a variation in gliadins and low-molecular-weight-glutenin subunits in both cultivars when treated with PGPM and biochar. This suggested improved grain quality, especially regarding the viscoelastic properties of the dough, when the filling period occurred in a dry climate. The results indicate that the application of biofertilisers and biochar may aid the effective management of sustainable wheat cultivation, to support environmental health without altering the biodiversity of the resident microbiome.

Perspective on utilization of Bacillus species as plant probiotics for different crops in adverse conditions

Plant probiotic bacteria are a versatile group of bacteria isolated from different environmental sources to improve plant productivity and immunity. The potential of plant probiotic-based formulations is successfully seen as growth enhancement in economically important plants. For instance, endophytic Bacillus species acted as plant growth-promoting bacteria, influenced crops such as cowpea and lady's finger, and increased phytochemicals in crops such as high antioxidant content in tomato fruits. The present review aims to summarize the studies of Bacillus species retaining probiotic properties and compare them with the conventional fertilizers on the market. Plant probiotics aim to take over the world since it is the time to rejuvenate and restore the soil and achieve sustainable development goals for the future. Comprehensive coverage of all the Bacillus species used to maintain plant health, promote plant growth, and fight against pathogens is crucial for establishing sustainable agriculture to face global change. Additionally, it will give the latest insight into this multifunctional agent with a detailed biocontrol mechanism and explore the antagonistic effects of Bacillus species in different crops.

Nanoparticle applications in agriculture: overview and response of plant-associated microorganisms

Globally, food security has become a critical concern due to the rise in human population and the current climate change crisis. Usage of conventional agrochemicals to maximize crop yields has resulted in the degradation of fertile soil, environmental pollution as well as human and agroecosystem health risks. Nanotechnology in agriculture is a fast-emerging and new area of research explored to improve crop productivity and nutrient-use efficiency using nano-sized agrochemicals at lower doses than conventional agrochemicals. Nanoparticles in agriculture are applied as nanofertilizers and/or nanopesticides. Positive results have been observed in terms of plant growth when using nano-based agricultural amendments. However, their continuous application may have adverse effects on plant-associated rhizospheric and endospheric microorganisms which often play a crucial role in plant growth, nutrient uptake, and disease prevention. While research shows that the application of nanoparticles has the potential to improve plant growth and yield, their effect on the diversity and function of plant-associated microorganisms remains under-explored. This review provides an overview of plant-associated microorganisms and their functions. Additionally, it highlights the response of plant-associated microorganisms to nanoparticle application and provides insight into areas of research required to promote sustainable and precision agricultural practices that incorporate nanofertilizers and nanopesticides.

Mitigating life-cycle environmental impacts and increasing net ecosystem economic benefits via optimized fertilization combined with lime in pomelo production in Southeast China

Excessive fertilization is acknowledged as a significant driver of heightened environmental pollution and soil acidification in agricultural production. Combining fertilizer optimization with soil acidity amendment can effectively achieve sustainable crop production in China, especially in Southeast China. However, there is a lack of long-term studies assessing the environmental and economic sustainability of combining fertilizer optimization with soil acidity amendment strategies, especially in fruit production. A four-year field experiment was conducted to explore pomelo yield, fruit quality, and environmental and economic performance in three treatments, e.g., local farmer practices (FP), optimized NPK fertilizer application (OPT), and OPT with lime (OPT+L). The results showed that the OPT+L treatment exhibited the highest pomelo yield and fruit quality among the three treatments. The OPT treatment had the lowest net greenhouse gas (GHG) emissions among the three treatments, which were 90.1 % and 42.6 % lower than those in FP and OPT+L, respectively. It is essential to note that GHG emissions associated with lime production constitute 40.7 % of the total emissions from fertilizer production. The OPT+L treatment reduced reactive nitrogen (Nr) emissions and phosphorus (P) losses, compared to FP and OPT. Moreover, the OPT+L treatment increased the net ecosystem economic benefit by 220.3 % and 20.3 % compared with the FP and OPT treatments, respectively. Overall, the OPT and OPT+L treatments underscore the potential to achieve environmentally friendly and economically sustainable pomelo production. Our study provides science-based evidence to achieve better environmental and economic performance in pomelo production through optimized NPK fertilization and alleviating soil acidification by lime.

Granular bacterial inoculant alters the rhizosphere microbiome and soil aggregate fractionation to affect phosphorus fractions and maize growth

The constraint of phosphorus (P) fixation on crop production in alkaline calcareous soils can be alleviated by applying bioinoculants. However, the impact of bacterial inoculants on this process remains inadequately understood. Here, a field study was conducted to investigate the effect of a high-concentration, cost-effective, and slow-release granular bacterial inoculant (GBI) on maize (Zea mays L.) plant growth. Additionally, we explored the effects of GBI on rhizosphere soil aggregate physicochemical properties, rhizosphere soil P fraction, and microbial communities within aggregates. The outcomes showed a considerable improvement in plant growth and P uptake upon application of the GBI. The application of GBI significantly enhanced the AP, phoD gene abundance, alkaline phosphatase activity, inorganic P fractions, and organic P fractions in large macroaggregates. Furthermore, GBI impacted soil aggregate fractionation, leading to substantial alterations in the composition of fungal and bacterial communities. Notably, key microbial taxa involved in P-cycling, such as Saccharimonadales and Mortierella, exhibited enrichment in the rhizosphere soil of plants treated with GBI. Overall, our study provides valuable insight into the impact of GBI application on microbial distributions and P fractions within aggregates of alkaline calcareous soils, crucial for fostering healthy root development and optimal crop growth potential. Subsequent research endeavors should delve into exploring the effects of diverse GBIs and specific aggregate types on P fraction and community composition across various soil profiles.

Integrating phytoremediation and mycoremediation with biosurfactant-producing fungi for hydrocarbon removal and the potential production of secondary resources

Treatment of petroleum-contaminated soil to a less toxic medium via physical and chemical treatment is too costly and requires posttreatment. This review focuses on the employment of phytoremediation and mycoremediation technologies in cleaning hydrocarbon-contaminated soil which is currently rare. It is considered environmentally beneficial and possibly cost-effective as it implements the synergistic interaction between plants and biosurfactant producing mycorrhiza to degrade hydrocarbon contaminants. This review also covers possible sources of hydrocarbon pollution in water and soil, toxicity effects, and current technologies for hydrocarbon removal and degradation. In addition to these problems, this review also discusses the challenges and opportunities of transforming the resultant treated sludge and treating plants into potential by-products for a higher quality of life for future generations.

The Biosynthesis, Accumulation of Phenolic Compounds and Antioxidant Response in Lactuca sativa L. Plants Inoculated with a Biofertilizer Based on Soil Yeast and Iron Nanoparticles

Lettuce is a vegetable that contributes vitamins, minerals, fibre, phenolic compounds and antioxidants to the human diet. In the search for improving production conditions and crop health, the use of microorganisms with plant growth-promoting capabilities, such as soil yeasts (PGPY), in conjunction with nanotechnology could offer sustainable development of agroecosystems. This study evaluated the synthesis of health-promoting bioactive compounds in lettuce under the application of soil yeast and an iron nanoparticle (NP-Fe2O3) encapsulated in alginate beads. Two yeast strains, Candida guillermondii and Rhodotorula mucilaginosa, and a consortium of both yeasts were used in the presence and absence of Fe2O3-NPs. Phenolic compounds were identified and quantified via HPLC-ESI-Q-ToF and antioxidant activity. Ten phenolic compounds were identified, highlighting the chicoric acid isomer and two quercetin glycosides with high concentrations of up to 100 µg g-1 in treatments with C. guillermondii. Treatments with R. mucilaginosa and NPs-Fe2O3 presented an increase in antioxidant activity, mainly in TEAC, CUPRAC and DPPH activities in leaves, with significant differences between treatments. Therefore, the use of encapsulated soil yeasts is a viable alternative for application in vegetables to improve the biosynthesis and accumulation of phenolic compounds in lettuce and other crops.

Degradation of Triazole Fungicides by Plant Growth-Promoting Bacteria from Contaminated Agricultural Soil

The widespread application of triazole fungicides (TFs) in agricultural practices can result in the considerable accumulation of active compound residues in the soil and a subsequent negative impact on the soil microbiota and crop health. In this study, we isolated three TF-degrading bacterial strains from contaminated agricultural soils and identified them as Klebsiella sp., Pseudomonas sp., and Citrobacter sp. based on analysis of morphological characteristics and 16S rRNA gene sequences. The strains used three common TFs, namely hexaconazole, difenoconazole, and propiconazole, as their only sources of carbon and energy for growth in a liquid mineral salt medium, with high concentrations (~ 500 mg/l) of each TF. In addition to the ability to degrade fungicides, the isolates also exhibited plant growth-promoting characteristics, such as nitrogen fixation, indole acetic acid production, phosphate dissolution, and cellulose degradation. The synergistic combination of three bacterial isolates significantly improved plant growth and development with an increased survival rate (57%), and achieved TF degradation ranging from 85.83 to 96.59% at a concentration of approximately 50 mg/kg of each TF within 45 days in the soil-plant system. Based on these findings, the three strains and their microbial consortium show promise for application in biofertilizers, to improve soil health and facilitate optimal plant growth.

Testing plant growth promoting microorganisms in the field - a proposal for standards

In the European Union and worldwide there are a burgeoning markets for plant growth promoting microorganisms (PGPM) and other biological agents as soil improvers, bio-fertilizers, plant bio-stimulants, and biological control agents or bio-pesticides. Microbial agents have a major share in this development. The use of such products is often advertised with the promise of contributing to sustainable agricultural practices by increasing crop growth and yield and offering an alternative or substitute to decrease the dependency of agriculture on hazardeous agrochemicals. In contrast to registered microbial plant protection products, PGPM that are marketed in the EU as soil improvers or plant biostimulants, are not strictly required to have proven minimum efficacy levels under field conditions. Manufacturers only have to ensure that these products do not pose unacceptable risks to human, animal or plant health, safety or the environment. Uniform guidelines comparable to the EPPO - standards (European and Mediterranean Plant Protection Organisation) to test the efficacy in field trials are not available. This paper attempts to fill the gap. It proposes guidelines for PGPM field trial design and implementation, as well as recommendations for the type and scope of data collection and evaluation. Selected research papers from literature were evaluated to analyze, whether and to what extent the requirements are already met. The majority of the papers had a clear experimental design followed by proper data evaluation. Frequent deficiencies were the low number of tested environments and crop species, insufficient site and agronomic management description and missing data on soil humidity and temperature. Using the suggested standards is assumed to increase the expressive power of tested microbial products.

Plant responses to climate change, how global warming may impact on food security: a critical review

Global agricultural production must double by 2050 to meet the demands of an increasing world human population but this challenge is further exacerbated by climate change. Environmental stress, heat, and drought are key drivers in food security and strongly impacts on crop productivity. Moreover, global warming is threatening the survival of many species including those which we rely on for food production, forcing migration of cultivation areas with further impoverishing of the environment and of the genetic variability of crop species with fall out effects on food security. This review considers the relationship of climatic changes and their bearing on sustainability of natural and agricultural ecosystems, as well as the role of omics-technologies, genomics, proteomics, metabolomics, phenomics and ionomics. The use of resource saving technologies such as precision agriculture and new fertilization technologies are discussed with a focus on their use in breeding plants with higher tolerance and adaptability and as mitigation tools for global warming and climate changes. Nevertheless, plants are exposed to multiple stresses. This study lays the basis for the proposition of a novel research paradigm which is referred to a holistic approach and that went beyond the exclusive concept of crop yield, but that included sustainability, socio-economic impacts of production, commercialization, and agroecosystem management.

A Review on Rhizosphere Microbiota of Tea Plant (Camellia sinensis L): Recent Insights and Future Perspectives

Rhizosphere microbial colonization of the tea plant provides many beneficial functions for the host, But the factors that influence the composition of these rhizosphere microbes and their functions are still unknown. In order to explore the interaction between tea plants and rhizosphere microorganisms, we summarized the current studies. First, the review integrated the known rhizosphere microbial communities of tea tree, including bacteria, fungi, and arbuscular mycorrhizal fungi. Then, various factors affecting tea rhizosphere microorganisms were studied, including: endogenous factors, environmental factors, and agronomic practices. Finally, the functions of rhizosphere microorganisms were analyzed, including (a) promoting the growth and quality of tea trees, (b) alleviating biotic and abiotic stresses, and (c) improving soil fertility. Finally, we highlight the gaps in knowledge of tea rhizosphere microorganisms and the future direction of development. In summary, understanding rhizosphere microbial interactions with tea plants is key to promoting the growth, development, and sustainable productivity of tea plants.

Streptomyces alleviate abiotic stress in plant by producing pteridic acids

Soil microbiota can confer fitness advantages to plants and increase crop resilience to drought and other abiotic stressors. However, there is little evidence on the mechanisms correlating a microbial trait with plant abiotic stress tolerance. Here, we report that Streptomyces effectively alleviate drought and salinity stress by producing spiroketal polyketide pteridic acid H (1) and its isomer F (2), both of which promote root growth in Arabidopsis at a concentration of 1.3 nM under abiotic stress. Transcriptomics profiles show increased expression of multiple stress responsive genes in Arabidopsis seedlings after pteridic acids treatment. We confirm in vivo a bifunctional biosynthetic gene cluster for pteridic acids and antimicrobial elaiophylin production. We propose it is mainly disseminated by vertical transmission and is geographically distributed in various environments. This discovery reveals a perspective for understanding plant-Streptomyces interactions and provides a promising approach for utilising beneficial Streptomyces and their secondary metabolites in agriculture to mitigate the detrimental effects of climate change.

Epigenetic and Hormonal Modulation in Plant-Plant Growth-Promoting Microorganism Symbiosis for Drought-Resilient Agriculture

Plant growth-promoting microorganisms (PGPMs) have emerged as valuable allies for enhancing plant growth, health, and productivity across diverse environmental conditions. However, the complex molecular mechanisms governing plant-PGPM symbiosis under the climatic hazard of drought, which is critically challenging global food security, remain largely unknown. This comprehensive review explores the involved molecular interactions that underpin plant-PGPM partnerships during drought stress, thereby offering insights into hormonal regulation and epigenetic modulation. This review explores the challenges and prospects associated with optimizing and deploying PGPMs to promote sustainable agriculture in the face of drought stress. In summary, it offers strategic recommendations to propel research efforts and facilitate the practical implementation of PGPMs, thereby enhancing their efficacy in mitigating drought-detrimental effects in agricultural soils.

Role of an antagonistic bacterium, Bacillus subtilis PE7, in growth promotion of netted melon (Cucumis melo L. var. reticulatus Naud.)

The aim of this study was to determine the plant growth-promoting effect of Bacillus subtilis PE7 on growth of melon plants. B. subtilis PE7 isolated from kimchi was identified based on colonial and microscopic morphology along with analyses of 16S rRNA and pycA gene sequences. Strain PE7 showed different levels of inhibition on phytopathogens and was able to grow at variable temperatures and pH values. Strain PE7 had the ability to produce siderophores, indole-3-acetic acid (IAA), ammonia, exopolysaccharides, and 1-aminocyclopropane-1-carboxylic acid deaminase, as well as solubilize insoluble phosphate and zinc. The IAA secretion of strain PE7 showed a concentration-dependent pattern based on the concentration of l-tryptophan supplemented in the fertilizer-based culture medium. The LC-MS analysis indicates the presence of IAA in the culture filtrate of strain PE7. Treatment of the B. subtilis PE7 culture containing different metabolites, mainly IAA, significantly promoted melon growth in terms of higher growth parameters and greater plant nutrient contents compared to treatments with the culture without IAA, fertilizer, and water. The cells of B. subtilis PE7 attached to and firmly colonized the roots of the bacterized melon plants. Based on our results, B. subtilis PE7 can be utilized as a potential microbial fertilizer to substitute chemical fertilizers in sustainable agriculture.

Microbial inoculants with higher capacity to colonize soils improved wheat drought tolerance

Microbial inoculants have gained increasing attention worldwide as an eco-friendly solution for improving agriculture productivity. Several studies have demonstrated their potential benefits, such as enhanced resistance to drought, salinity, and pathogens. However, the beneficial impacts of inoculants remain inconsistent. This variability is attributed to limited knowledge of the mechanisms by which microbial inoculants affect crop growth and a lack of ecological characteristics of these inoculants that limit our ability to predict their beneficial effects. The first important step is believed to be the evaluation of the inoculant's ability to colonize new habitats (soils and plant roots), which could provide crops with beneficial functions and improve the consistency and efficiency of the inoculants. In this study, we aimed to investigate the impact of three microbial inoculants (two bacterial: P1 and P2, and one fungal: P3) on the growth and stress responses of three wheat varieties in two different soil types under drought conditions. Furthermore, we investigated the impact of microbial inoculants on soil microbial communities. Plant biomass and traits were measured, and high-throughput sequencing was used to characterize bulk and rhizosphere soil microbiomes after exposure to drought stress. Under drought conditions, plant shoot weight significantly increased (11.37%) under P1 treatments compared to uninoculated controls. In addition, total nitrogen enzyme activity increased significantly under P1 in sandy soil but not in clay soil. Importantly, network analyses revealed that P1, consisting of Bacillus paralicheniformis and Bacillus subtilis, emerged as the keystone taxa in sandy soil. Conversely, P2 and P3 failed to establish as keystone taxa, which may explain their insignificant impact on wheat performance under drought conditions. In conclusion, our study emphasizes the importance of effective colonization by microbial inoculants in promoting crop growth under drought conditions. Our findings support the development of microbial inoculants that robustly colonize plant roots for improved agricultural productivity.

Mitigating climate change and pandemic impacts on global food security: dual sustainable agriculture approach (2S approach)

MAIN CONCLUSION

Simultaneous application of two sustainability approaches such as the application of biofertilizers to GM plants and microbe bioengineering to enhance physiological response and beneficial interaction with GM plants may have a significant impact on strengthening global food security amid climate change and the pandemic. The second sustainable development goal (SDG 02, Zero Hunger) aims global agricultural sustainability and food security challenges. The agriculture sector has been an integral part of developing countries for millions of farmers and their families. Their contribution provides stability of raw matter related to food availability. But climate change, higher population growth and worldwide pandemics are the main obstacles to food quality, higher crop productivity and global food security. Scientists are concerned with the manifestation of agriculture sustainability in the modern crop management approach to resolving the issues. It is the only way to higher yield productivity by protecting the environment, conserving natural resources, and slowing climate change. Several strategies can be an option to implement, yet the proposed two sustainability approach or 2S approach will be the significant way toward the goal of zero hunger. The first sustainability approach is an application of genetically modified (S1: GMO) Plants and the other is an application of beneficiary plant growth-promoting microbes (S2: Biofertilizers) to the plants for both higher crops and maintenance of the environment. This study summarizes the essential points of S1 and S2 for the widespread utilization of the 2S approach in agriculture and recommends the potential alternatives to be implemented to produce food for all. Simultaneous application of the 2S approach can defeat all threats to gain sustainability in agriculture.

Rare rhizo-Actinomycetes: A new source of agroactive metabolites

Numerous biotic and abiotic stress in some geographical regions predisposed their agricultural matrix to challenges threatening plant productivity, health, and quality. In curbing these threats, different customary agrarian principles have been created through research and development, ranging from chemical inputs and genetic modification of crops to the recently trending smart agricultural technology. But the peculiarities associated with these methods have made agriculturists rely on plant rhizospheric microbiome services, particularly bacteria. Several bacterial resources like Proteobacteria, Firmicutes, Acidobacteria, and Actinomycetes (Streptomycetes) are prominent as bioinoculants or the application of their by-products in alleviating biotic/abiotic stress have been extensively studied, with a dearth in the application of rare Actinomycetes metabolites. Rare Actinomycetes are known for their colossal genome, containing well-preserved genes coding for prolific secondary metabolites with many agroactive functionalities that can revolutionize the agricultural industry. Therefore, the imperativeness of this review to express the occurrence and distributions of rare Actinomycetes diversity, plant and soil-associated habitats, successional track in the rhizosphere under diverse stress, and their agroactive metabolite characteristics and functionalities that can remediate the challenges associated with agricultural productivity.

Beneficial microbial consortium improves winter rye performance by modulating bacterial communities in the rhizosphere and enhancing plant nutrient acquisition

The beneficial effect of microbial consortium application on plants is strongly affected by soil conditions, which are influenced by farming practices. The establishment of microbial inoculants in the rhizosphere is a prerequisite for successful plant-microorganism interactions. This study investigated whether a consortium of beneficial microorganisms establishes in the rhizosphere of a winter crop during the vegetation period, including the winter growing season. In addition, we aimed for a better understanding of its effect on plant performance under different farming practices. Winter rye plants grown in a long-time field trial under conventional or organic farming practices were inoculated after plant emergence in autumn with a microbial consortium containing Pseudomonas sp. (RU47), Bacillus atrophaeus (ABi03) and Trichoderma harzianum (OMG16). The density of the microbial inoculants in the rhizosphere and root-associated soil was quantified in autumn and the following spring. Furthermore, the influence of the consortium on plant performance and on the rhizosphere bacterial community assembly was investigated using a multidisciplinary approach. Selective plating showed a high colonization density of individual microorganisms of the consortium in the rhizosphere and root-associated soil of winter rye throughout its early growth cycle. 16S rRNA gene amplicon sequencing showed that the farming practice affected mainly the rhizosphere bacterial communities in autumn and spring. However, the microbial consortium inoculated altered also the bacterial community composition at each sampling time point, especially at the beginning of the new growing season in spring. Inoculation of winter rye with the microbial consortium significantly improved the plant nutrient status and performance especially under organic farming. In summary, the microbial consortium showed sufficient efficacy throughout vegetation dormancy when inoculated in autumn and contributed to better plant performance, indicating the potential of microbe-based solutions in organic farming where nutrient availability is limited.

Enhancing Phosphorus and Nitrogen Uptake in Maize Crops with Food Industry Biosolids and Azotobacter nigricans

The problem of phosphorus and nitrogen deficiency in agricultural soils has been solved by adding chemical fertilizers. However, their excessive use and their accumulation have only contributed to environmental contamination. Given the high content of nutrients in biosolids collected from a food industry waste treatment plant, their use as fertilizers was investigated in Zea mays plants grown in sandy loam soil collected from a semi-desert area. These biosolids contained insoluble phosphorus sources; therefore, given the ability of Azotobacter nigricans to solubilize phosphates, this strain was incorporated into the study. In vitro, the suitable conditions for the growth of Z. mays plants were determined by using biosolids as a fertilizer and A. nigricans as a plant-growth-promoting microorganism; in vitro, the ability of A. nigricans to solubilize phosphates, fix nitrogen, and produce indole acetic acid, a phytohormone that promotes root formation, was also evaluated. At the greenhouse stage, the Z. mays plants fertilized with biosolids at concentrations of 15 and 20% (v/w) and inoculated with A. nigricans favored the development of bending strength plants, which was observed on the increased stem diameter (>13.5% compared with the negative control and >7.4% compared with the positive control), as well as a better absorption of phosphorus and nitrogen, the concentration of which increased up to 62.8% when compared with that in the control treatments. The interactions between plants and A. nigricans were observed via scanning electron microscopy. The application of biosolids and A. nigricans in Z. mays plants grown in greenhouses presented better development than when Z. mays plants were treated with a chemical fertilizer. The enhanced plant growth was attributed to the increase in root surface area.

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.

Implications of Below-Ground Allelopathic Interactions of Camelina sativa and Microorganisms for Phosphate Availability and Habitat Maintenance

Toxic breakdown products of young Camelina sativa (L.) Crantz, glucosinolates can eliminate microorganisms in the soil. Since microorganisms are essential for phosphate cycling, only insensitive microorganisms with phosphate-solubilizing activity can improve C. sativa's phosphate supply. In this study, 33P-labeled phosphate, inductively coupled plasma mass spectrometry and pot experiments unveiled that not only Trichoderma viride and Pseudomonas laurentiana used as phosphate-solubilizing inoculants, but also intrinsic soil microorganisms, including Penicillium aurantiogriseum, and the assemblies of root-colonizing microorganisms solubilized as well phosphate from apatite, trigger off competitive behavior between the organisms. Driving factors in the competitiveness are plant and microbial secondary metabolites, while glucosinolates of Camelina and their breakdown products are regarded as key compounds that inhibit the pathogen P. aurantiogriseum, but also seem to impede root colonization of T. viride. On the other hand, fungal diketopiperazine combined with glucosinolates is fatal to Camelina. The results may contribute to explain the contradictory effects of phosphate-solubilizing microorganisms when used as biofertilizers. Further studies will elucidate impacts of released secondary metabolites on coexisting microorganisms and plants under different environmental conditions.

Microbial applications for sustainable space exploration beyond low Earth orbit

With the construction of the International Space Station, humans have been continuously living and working in space for 22 years. Microbial studies in space and other extreme environments on Earth have shown the ability for bacteria and fungi to adapt and change compared to "normal" conditions. Some of these changes, like biofilm formation, can impact astronaut health and spacecraft integrity in a negative way, while others, such as a propensity for plastic degradation, can promote self-sufficiency and sustainability in space. With the next era of space exploration upon us, which will see crewed missions to the Moon and Mars in the next 10 years, incorporating microbiology research into planning, decision-making, and mission design will be paramount to ensuring success of these long-duration missions. These can include astronaut microbiome studies to protect against infections, immune system dysfunction and bone deterioration, or biological in situ resource utilization (bISRU) studies that incorporate microbes to act as radiation shields, create electricity and establish robust plant habitats for fresh food and recycling of waste. In this review, information will be presented on the beneficial use of microbes in bioregenerative life support systems, their applicability to bISRU, and their capability to be genetically engineered for biotechnological space applications. In addition, we discuss the negative effect microbes and microbial communities may have on long-duration space travel and provide mitigation strategies to reduce their impact. Utilizing the benefits of microbes, while understanding their limitations, will help us explore deeper into space and develop sustainable human habitats on the Moon, Mars and beyond.

The Microbial Connection to Sustainable Agriculture

Microorganisms are an important element in modeling sustainable agriculture. Their role in soil fertility and health is crucial in maintaining plants' growth, development, and yield. Further, microorganisms impact agriculture negatively through disease and emerging diseases. Deciphering the extensive functionality and structural diversity within the plant-soil microbiome is necessary to effectively deploy these organisms in sustainable agriculture. Although both the plant and soil microbiome have been studied over the decades, the efficiency of translating the laboratory and greenhouse findings to the field is largely dependent on the ability of the inoculants or beneficial microorganisms to colonize the soil and maintain stability in the ecosystem. Further, the plant and its environment are two variables that influence the plant and soil microbiome's diversity and structure. Thus, in recent years, researchers have looked into microbiome engineering that would enable them to modify the microbial communities in order to increase the efficiency and effectiveness of the inoculants. The engineering of environments is believed to support resistance to biotic and abiotic stressors, plant fitness, and productivity. Population characterization is crucial in microbiome manipulation, as well as in the identification of potential biofertilizers and biocontrol agents. Next-generation sequencing approaches that identify both culturable and non-culturable microbes associated with the soil and plant microbiome have expanded our knowledge in this area. Additionally, genome editing and multidisciplinary omics methods have provided scientists with a framework to engineer dependable and sustainable microbial communities that support high yield, disease resistance, nutrient cycling, and management of stressors. In this review, we present an overview of the role of beneficial microbes in sustainable agriculture, microbiome engineering, translation of this technology to the field, and the main approaches used by laboratories worldwide to study the plant-soil microbiome. These initiatives are important to the advancement of green technologies in agriculture.

Effect of sterilants and plant growth regulators in regenerating commonly used cassava cultivars at the Kenyan coast

Cassava is an important root crop whose seed system is undeveloped. Micropropagation of explants in vitro has the potential of addressing the challenge of the unavailability of healthy cassava planting materials. Therefore, the study determined the effect of sterilization and plant growth regulators on cassava explants to produce certified disease-free plants of commonly used cultivars at the coast of Kenya. The apical nodes drawn from the three cultivars of cassava, Tajirika and Kibandameno and Taita, were used as explants. The sterilant sodium hypochlorite (NaOCl) at 5, 10 and 15% and 70% ethanol for 1 and 5 min and sprayed for 20 s were tested for the effect on the explant. Similarly, the effect of BAP (6-Benzyl amino purine) and NAA (1-Naphthalene acetic acid) Plant Growth Regulators (PGRs) each at 0.5, 1 and 5 mg/L under optimal conditions of sterilization was determined. Surface sterilization using 10% NaOCl followed by spraying 70% ethanol for 20 s had 85% initiation on Tajirika whereas 5% NaOCl followed by spraying 70% ethanol for 20 s had 87% and 91% initiation in Kibandameno and Taita cultivars, respectively. In Tajirika, significantly (p < 0.05) high shooting of 68% was from 5 mg/L BAP in MS media whereas approximately 50% rooting was from either 0.5 mg/L BAP or 5 mg/L NAA in MS media. Kibandameno and Taita cultivars had approximately 50% shooting from MS media without PGRs. Kibandameno had >37% rooting from 0.5 to 5 mg/L BAP or NAA in MS media whereas Taita had approximately 50% rooting from 0 to 5 mg/L NAA in MS media. This protocol showed at least 50% success rate of initiation, shooting and rooting as a rapid multiplication regeneration of Tajirika and Kibandameno and Taita cultivar plantlets with little modification of humidity and temperatures in the growth chambers. This protocol requires validation for use in large-scale production of cassava plantlets to alleviate the inadequacy of cassava planting materials among farmers.

New seed coating containing Trichoderma viride with anti-pathogenic properties

Background

To ensure food security in the face of climate change and the growing world population, multi-pronged measures should be taken. One promising approach uses plant growth-promoting fungi (PGPF), such as Trichoderma, to reduce the usage of agrochemicals and increase plant yield, stress tolerance, and nutritional value. However, large-scale applications of PGPF have been hampered by several constraints, and, consequently, usage on a large scale is still limited. Seed coating, a process that consists of covering seeds with low quantities of exogenous materials, is gaining attention as an efficient and feasible delivery system for PGPF.

Methods

We have designed a new seed coating composed of chitin, methylcellulose, and Trichoderma viride spores and assessed its effect on canola (Brassica napus L.) growth and development. For this purpose, we analyzed the antifungal activity of T. viride against common canola pathogenic fungi (Botrytis cinerea, Fusarium culmorum, and Colletotrichum sp.). Moreover, the effect of seed coating on germination ratio and seedling growth was evaluated. To verify the effect of seed coating on plant metabolism, we determined superoxide dismutase (SOD) activity and expression of the stress-related RSH (RelA/SpoT homologs).

Results

Our results showed that the T. viride strains used for seed coating significantly restricted the growth of all three pathogens, especially F. culmorum, for which the growth was inhibited by over 40%. Additionally, the new seed coating did not negatively affect the ability of the seeds to complete germination, increased seedling growth, and did not induce the plant stress response. To summarize, we have successfully developed a cost-effective and environmentally responsible seed coating, which will also be easy to exploit on an industrial scale.

Solid-State Fermentation: Applications and Future Perspectives for Biostimulant and Biopesticides Production

With the expansion of the green products market and the worldwide policies and strategies directed toward a green revolution and ecological transition, the demand for innovative approaches is always on the rise. Among the sustainable agricultural approaches, microbial-based products are emerging over time as effective and feasible alternatives to agrochemicals. However, the production, formulation, and commercialization of some products can be challenging. Among the main challenges are the industrial production processes that ensure the quality of the product and its cost on the market. In the context of a circular economy, solid-state fermentation (SSF) might represent a smart approach to obtaining valuable products from waste and by-products. SSF enables the growth of various microorganisms on solid surfaces in the absence or near absence of free-flowing water. It is a valuable and practical method and is used in the food, pharmaceutical, energy, and chemical industries. Nevertheless, the application of this technology in the production of formulations useful in agriculture is still limited. This review summarizes the literature dealing with SSF agricultural applications and the future perspective of its use in sustainable agriculture. The survey showed good potential for SSF to produce biostimulants and biopesticides useful in agriculture.

Mycorrhizal Colonization of Wheat by Intact Extraradical Mycelium of Mn-Tolerant Native Plants Induces Different Biochemical Mechanisms of Protection

Soil with excess Mn induces toxicity and impairs crop growth. However, with the development in the soil of an intact extraradical mycelia (ERM) from arbuscular mycorrhizal fungi (AMF) symbiotic to native Mn-tolerant plants, wheat growth is promoted due to a stronger AMF colonization and subsequent increased protection against Mn toxicity. To determine the biochemical mechanisms of protection induced by this native ERM under Mn toxicity, wheat grown in soil from previously developed Lolium rigidum (LOL) or Ornithopus compressus (ORN), both strongly mycotrophic plants, was compared to wheat grown in soil from previously developed Silene gallica (SIL), a non-mycotrophic plant. Wheat grown after LOL or ORN had 60% higher dry weight, ca. two-fold lower Mn levels and almost double P contents. Mn in the shoots was preferentially translocated to the apoplast along with Mg and P. The activity of catalase increased; however, guaiacol peroxidase (GPX) and superoxide dismutase (SOD) showed lower activities. Wheat grown after ORN differed from that grown after LOL by displaying slightly higher Mn levels, higher root Mg and Ca levels and higher GPX and Mn-SOD activities. The AMF consortia established from these native plants can promote distinct biochemical mechanisms for protecting wheat against Mn toxicity.

Influence of Plant Growth-Promoting Rhizobacteria on the Formation of Apoplastic Barriers and Uptake of Water and Potassium by Wheat Plants

The formation of apoplastic barriers is important for controlling the uptake of water and ions by plants, thereby influencing plant growth. However, the effects of plant growth-promoting bacteria on the formation of apoplastic barriers, and the relationship between these effects and the ability of bacteria to influence the content of hormones in plants, have not been sufficiently studied. The content of cytokinins, auxins and potassium, characteristics of water relations, deposition of lignin and suberin and the formation of Casparian bands in the root endodermis of durum wheat (Triticum durum Desf.) plants were evaluated after the introduction of the cytokinin-producing bacterium Bacillus subtilis IB-22 or the auxin-producing bacterium Pseudomonas mandelii IB-Ki14 into their rhizosphere. The experiments were carried out in laboratory conditions in pots with agrochernozem at an optimal level of illumination and watering. Both strains increased shoot biomass, leaf area and chlorophyll content in leaves. Bacteria enhanced the formation of apoplastic barriers, which were most pronounced when plants were treated with P. mandelii IB-Ki14. At the same time, P. mandelii IB-Ki14 caused no decrease in the hydraulic conductivity, while inoculation with B. subtilis IB-22, increased hydraulic conductivity. Cell wall lignification reduced the potassium content in the roots, but did not affect its content in the shoots of plants inoculated with P. mandelii IB-Ki14. Inoculation with B. subtilis IB-22 did not change the potassium content in the roots, but increased it in the shoots.

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.

Can arbuscular mycorrhizal fungi and rhizobacteria facilitate 33P uptake in maize plants under water stress?

Arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) are able to provide key ecosystem services, protecting plants against biotic and abiotic stresses. Here, we hypothesized that a combination of AMF (Rhizophagus clarus) and PGPR (Bacillus sp.) could enhance ³³P uptake in maize plants under soil water stress. A microcosm experiment using mesh exclusion and a radiolabeled phosphorus tracer (³³P) was installed using three types of inoculation: i) only AMF, ii) only PGPR, and iii) a consortium of AMF and PGPR, alongside a control treatment without inoculation. For all treatments, a gradient of three water-holding capacities (WHC) was considered i) 30% (severe drought), ii) 50% (moderate drought), and iii) 80% (optimal condition, no water stress). In severe drought conditions, AMF root colonization of dual-inoculated plants was significantly lower compared to individual inoculation of the AMF, whilst ³³P uptake by dual-inoculated plants or plants inoculated with bacteria was 2.4-fold greater than the uninoculated treatment. Under moderate drought conditions the use of AMF promoted the highest ³³P uptake by plants, increasing it by 2.1-fold, when compared to the uninoculated treatment. Without drought stress, AMF showed the lowest ³³P uptake and, overall, plant P acquisition was lower for all inoculation types when compared to the severe and moderate drought treatments. The total shoot P content was modulated by the water-holding capacity and inoculation type, with the lowest values observed under severe drought and the highest values under moderate drought. The highest soil electrical conductivity (EC) values were found under severe drought in AMF-inoculated plants and the lowest EC for no drought in single or dual-inoculated plants. Furthermore, water-holding capacity influenced the total soil bacterial and mycorrhizal abundance over time, with the highest abundances being found under severe and moderate drought. This study demonstrates that the positive influence of microbial inoculation on ³³P uptake by plants varied with soil water gradient. Furthermore, under severe stress conditions, AMF invested more in the production of hyphae, vesicles and spore production, indicating a significant carbon drain from the host plant as evidenced by the lack of translation of increased ³³P uptake into biomass. Therefore, under severe drought the use of bacteria or dual-inoculation seems to be more effective than individual AMF inoculation in terms of ³³P uptake by plants, while under moderate drought, the use of AMF stood out.

Promotion of Peanut (Arachis hypogaea L.) Growth by Plant Growth-Promoting Microorganisms

Brazil is an important peanut producer, but despite its high production, there still needs to be an inoculant for the peanut crop. In addition, the use of microorganisms that promote plant growth (PGPM) is not common, and this crop is highly dependent on chemical fertilizers. An excellent alternative to reduce the use of fertilizers and chemical inputs in peanut crops while reducing the production cost and environmental impact is the use of PGPM. The objective of this study was to evaluate the effects of Azospirillum brasilense, Bacillus subtilis, Bradyrhizobium japonicum, and Trichoderma harzianum as single inoculants and co-inoculants on the growth promotion and productivity of peanuts in greenhouse and field conditions. In the greenhouse, the experiment was conducted with 12 treatments with six repetitions. In the field conditions, the experiment was conducted with five treatments with four repetitions. Both experiments were conducted in randomized blocks. In general, all the microorganisms evaluated in the present study promoted increases in root dry mass, shoot dry mass, phosphorus concentrations, and plant height in the greenhouse and under field conditions compared with the control. Interestingly, the mixtures of microorganisms inoculated in peanut plants did not promote greater plant growth and development compared with inoculations of the microorganisms separately. Specifically, in the field, the highest productivity was found for the inoculation of B. japonicum alone. The PGPM evaluated in the present study for peanut crops generally promoted some increases in productivity in greenhouse and field conditions.

Insights into the genome of Methylobacterium sp. NMS14P, a novel bacterium for growth promotion of maize, chili, and sugarcane

A novel methylotrophic bacterium designated as NMS14P was isolated from the root of an organic coffee plant (Coffea arabica) in Thailand. The 16S rRNA sequence analysis revealed that this new isolate belongs to the genus Methylobacterium, and its novelty was clarified by genomic and comparative genomic analyses, in which NMS14P exhibited low levels of relatedness with other Methylobacterium-type strains. NMS14P genome consists of a 6,268,579 bp chromosome, accompanied by a 542,519 bp megaplasmid and a 66,590 bp plasmid, namely pNMS14P1 and pNMS14P2, respectively. Several genes conferring plant growth promotion are aggregated on both chromosome and plasmids, including phosphate solubilization, indole-3-acetic acid (IAA) biosynthesis, cytokinins (CKs) production, 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity, sulfur-oxidizing activity, trehalose synthesis, and urea metabolism. Furthermore, pangenome analysis showed that NMS14P possessed the highest number of strain-specific genes accounting for 1408 genes, particularly those that are essential for colonization and survival in a wide array of host environments, such as ABC transporter, chemotaxis, quorum sensing, biofilm formation, and biosynthesis of secondary metabolites. In vivo tests have supported that NMS14P significantly promoted the growth and development of maize, chili, and sugarcane. Collectively, NMS14P is proposed as a novel plant growth-promoting Methylobacterium that could potentially be applied to a broad range of host plants as Methylobacterium-based biofertilizers to reduce and ultimately substitute the use of synthetic agrochemicals for sustainable agriculture.

Removal of primary nutrient degraders reduces growth of soil microbial communities with genomic redundancy

Introduction

Understanding how microorganisms within a soil community interact to support collective respiration and growth remains challenging. Here, we used a model substrate, chitin, and a synthetic Model Soil Consortium (MSC-2) to investigate how individual members of a microbial community contribute to decomposition and community growth. While MSC-2 can grow using chitin as the sole carbon source, we do not yet know how the growth kinetics or final biomass yields of MSC-2 vary when certain chitin degraders, or other important members, are absent.

Methods

To characterize specific roles within this synthetic community, we carried out experiments leaving out members of MSC-2 and measuring biomass yields and CO2 production. We chose two members to iteratively leave out (referred to by genus name): Streptomyces, as it is predicted via gene expression analysis to be a major chitin degrader in the community, and Rhodococcus as it is predicted via species co-abundance analysis to interact with several other members.

Results

Our results showed that when MSC-2 lacked Streptomyces, growth and respiration of the community was severely reduced. Removal of either Streptomyces or Rhodococcus led to major changes in abundance for several other species, pointing to a comprehensive shifting of the microbial community when important members are removed, as well as alterations in the metabolic profile, especially when Streptomyces was lacking. These results show that when keystone, chitin degrading members are removed, other members, even those with the potential to degrade chitin, do not fill the same metabolic niche to promote community growth. In addition, highly connected members may be removed with similar or even increased levels of growth and respiration.

Discussion

Our findings are critical to a better understanding of soil microbiology, specifically in how communities maintain activity when biotic or abiotic factors lead to changes in biodiversity in soil systems.

Bacillus proteolyticus OSUB18 triggers induced systemic resistance against bacterial and fungal pathogens in Arabidopsis

Pseudomonas syringae and Botrytis cinerea cause destructive bacterial speck and grey mold diseases in many plant species, leading to substantial economic losses in agricultural production. Our study discovered that the application of Bacillus proteolyticus strain OSUB18 as a root-drench enhanced the resistance of Arabidopsis plants against P. syringae and B. cinerea through activating Induced Systemic Resistance (ISR). The underlying mechanisms by which OSUB18 activates ISR were studied. Our results revealed that the Arabidopsis plants with OSUB18 root-drench showed the enhanced callose deposition and ROS production when inoculated with Pseudomonas syringae and Botrytis cinerea pathogens, respectively. Also, the increased salicylic acid (SA) levels were detected in the OSUB18 root-drenched plants compared with the water root-drenched plants after the P. syringae infection. In contrast, the OSUB18 root-drenched plants produced significantly higher levels of jasmonyl isoleucine (JA-Ile) than the water root-drenched control after the B. cinerea infection. The qRT-PCR analyses indicated that the ISR-responsive gene MYC2 and the ROS-responsive gene RBOHD were significantly upregulated in OSUB18 root-drenched plants upon both pathogen infections compared with the controls. Also, twenty-four hours after the bacterial or fungal inoculation, the OSUB18 root-drenched plants showed the upregulated expression levels of SA-related genes (PR1, PR2, PR5, EDS5, and SID2) or JA-related genes (PDF1.2, LOX3, JAR1 and COI1), respectively, which were consistent with the related hormone levels upon these two different pathogen infections. Moreover, OSUB18 can trigger ISR in jar1 or sid2 mutants but not in myc2 or npr1 mutants, depending on the pathogen's lifestyles. In addition, OSUB18 prompted the production of acetoin, which was reported as a novel rhizobacterial ISR elicitor. In summary, our studies discover that OSUB18 is a novel ISR inducer that primes plants' resistance against bacterial and fungal pathogens by enhancing the callose deposition and ROS accumulation, increasing the production of specific phytohormones and other metabolites involved in plant defense, and elevating the expression levels of multiple defense genes.

Structural breakdown and phytotoxic assessments of PE degradation through acid hydrolysis, starch addition and Pseudomonas aeruginosa bioremediation

Vast amounts of plastic waste are causing serious environmental issues and urge to develop of new remediation methods. The aim of the study is to determine the role of inorganic (nitric acid), organic (starch addition), and biological (Pseudomonas aeruginosa) soil amendments on the degradation of Polyethylene (PE) and phytotoxic assessment for the growth of lettuce plant. The PE-degrading bacteria were isolated from the plastic-contaminated soil. The strain was identified as Pseudomonas aeruginosa (OP007126) and showed the highest degradation percentage for PE. PE was pre-treated with nitric acid as well as starch and incubated in the soil, whereas P. aeruginosa was also inoculated in PE-contaminated soils. Different combinations were also tested. FTIR analysis and weight reduction showed that though nitric acid was efficient in degradation, the combined application of starch and bacteria also showed effective degradation of PE. Phytotoxicity was assessed using morphological, physiological, and biochemical parameters of plant. Untreated PE significantly affected plants' physiology, resulting in a 45% reduction in leaf chlorophyll and a 40% reduction in relative water content. It also had adverse effects on the biochemical parameters of lettuce. Bacterial inoculation and starch treatment mitigated the harmful impact of stress and improved plants' growth as well as physiological and biochemical parameters; however, the nitric treatment proved phytotoxic. The observed results revealed that bacteria and starch could be effectively used for the degradation of pre-treated PE.

Integrated analysis of potential microbial consortia, soil nutritional status, and agro-climatic datasets to modulate P nutrient uptake and yield effectiveness of wheat under climate change resilience

Climate change has a devastating effect on wheat production; therefore, crop production might decline by 2030. Phosphorus (P) nutrient deficiency is another main limiting factor of reduced yield. Hence, there is a dire need to judiciously consider wheat yield, so that human requirements and nutrition balance can be sustained efficiently. Despite the great significance of biostimulants in sustainable agriculture, there is still a lack of integrated technology encompassing the successful competitiveness of inoculated phosphate-solubilizing bacteria (PSB) in agricultural systems in the context of climatic conditions/meteorological factors and soil nutritional status. Therefore, the present study reveals the modulation of an integrated P nutrient management approach to develop potential PSB consortia for recommended wheat varieties by considering the respective soil health and agro-climatic conditions. The designed consortia were found to maintain adequate viability for up to 9 months, verified through field emission scanning electron microscopy and viable count. Furthermore, a significant increase in grain yield (5%-8%) and seed P (4%) content was observed in consortia-inoculated wheat plants with 20% reduced Diammonium phosphate (DAP) application under net house conditions. Fluorescence in situ hybridization analysis of roots and amplification of the gcd gene of Ochrobactrum sp. SSR indicated the survival and rhizosphere competency of the inoculated PSB. Categorical principal component analysis (CAT-PCA) showed a positive correlation of inoculated field-grown wheat varieties in native soils to grain yield, soil P content, and precipitation for sites belonging to irrigated plains and seed P content, soil organic matter, and number of tillers for sites belonging to Northern dry mountains. However, the impact of inoculation at sites belonging to the Indus delta was found significantly correlated to soil potassium (K) content, electrical conductivity (EC), and temperature. Additionally, a significant increase in grain yield (15%) and seed P (14%) content was observed in inoculated wheat plants. Thus, the present study demonstrates for the first time the need to integrate soil biological health and agro-climatic conditions for consistent performance of augmented PSB and enhanced P nutrient uptake to curtail soil pollution caused by the extensive use of agrochemicals. This study provides innovative insights and identifies key questions for future research on PSB to promote its successful implementation in agriculture.