Biofertilizers: An Emerging Trend in Agricultural Sustainability

In this study, the effectiveness of plant growth promoting fungus (PGPF) and plant growth promoting rhizobacteria (PGPR) on Bhendi (Abelmoschus esculentus (L.) Moench) was estimated. Germination study was conducted with Bhendi seeds treated in different PGPR and PGPF. The growth indices like vigour index, seedling growth, shoot length, root length, total leaf area, fresh weight and dry weight and yield parameters were taken into consideration for this experiment. All these morphological growth parameters gradually increased with PGPF and PGPR when compared to control. On the basis of germination study data, the best growth of bhendi seedling was recorded in PGPF followed by PGPR when compare with control.

The consistent use of synthetic fertilizers and chemicals in traditional agriculture has not only compromised the fragile agroecosystems but has also adversely affected human, aquatic, and terrestrial life. The use of phytostimulants is an alternative eco-friendly approach that eliminates ecosystem disruption while maintaining agricultural productivity. Phytostimulants include living entities and materials, such as microorganisms and nanomaterials, which when applied to plants or to the rhizosphere, stimulate plant growth and induce tolerance to plants against biotic and abiotic stresses. In this review, we focus on plant growth-promoting rhizobacteria (PGPR), beneficial fungi, such as arbuscular mycorrhizal fungi (AMF) and plant growth-promoting fungi (PGPF), actinomycetes, cyanobacteria, azolla, and lichens, and their potential benefits in the crop improvement, and mitigation of abiotic and biotic stresses either alone or in combination. PGPR, AMF, and PGPF are plant beneficial microbes that can release phytohormones, such as indole acetic acid (IAA), gibberellic acid (GA), and cytokinins, promoting plant growth and improving soil health, and in addition, they also produce many secondary metabolites, antibiotics, and antioxidant compounds and help to combat biotic and abiotic stresses. Their ability to act as phytostimulator and a supplement of inorganic fertilizers is considered promising in practicing sustainable agriculture and organic farming. Glomalin is a proteinaceous product, produced by AMF, involved in soil aggregation and elevation of soil water holding capacity under stressed and unstressed conditions. The negative effects of continuous cropping can be mitigated by AMF biofertilization. The synergistic effects of PGPR and PGPF may be more effective. The mechanisms of control exercised by PGPF either direct or indirect to suppress plant diseases viz. by competing for space and nutrients, mycoparasitism, antibiosis, mycovirus-mediated cross-protection, and induced systemic resistance (ISR) have been discussed. The emerging role of cyanobacterial metabolites and the implication of nanofertilizers have been highlighted in sustainable agriculture.

Rhizosphere is the most important ecological niche, which plays a vital role by acting as a connecting link between plant, soil and microbes. Rhizo-deposits are the secretions released by the plant roots in the form of root exudates, border cells of roots and other rhizo-deposits. These secretions mostly include low molecular weight bioactive organic compounds, which may attract various beneficial microbes like PGPR (plant growth promoting rhizobacteria), PGPF (plant growth promoting fungi) for their colonization and some of them also contain antimicrobial defensive compounds that repel various deleterious or plant pathogenic microorganisms. Among several forms of benefits derived from rhizo-deposits, root exudates that help in attracting and harbouring various beneficial microbes like rhizobacteria and fungal bio-agents, play a crucial role in the suppression of various soil borne plant pathogens, insect pests, nematodes and harmful microbes apart from their growth promoting activities. These PGPR, PGPF, and various microorganisms with bio-control potential exhibit excellent colonizing ability with the roots and even some of them establish symbiotic and endophytic relationship with plants. These beneficial microbes colonizing the rhizosphere zone exhibit various types of mechanisms like nutrient solubilization by supplying water and inorganic mineral nutrients in the available form to the plant. They exhibit various defence mechanisms like hyper-parasitism, competition, antibiosis and induced systemic resistance response in plants against plant pathogenic and harmful microbes. In addition to these bio-control activities, these beneficial microbes like PGPR’s and PGPF’s present in the rhizosphere region help in the enhancement of plant growth parameters like shoot and root length, shoot and root biomass, chlorophyll content, vigour, flowering, fruiting and ultimately yield of plants. They also help in alleviating several abiotic stress in plants such as water scarcity, submergence and salinity. This chapter provides the insights into, how bacterial and fungal biocontrol agents help the crop plants in combating several biotic and abiotic stresses through several morphological and phsiological changes in the crop due to application of biocontrol agents and also that how these microorganisms help plants in increasing their growth and vigour. How root exudates help in colonization of various rhizosphere-inhabiting microorganisms and how application of various organic substrates and de-oiled cakes in the rhizosphere zone help in the population build-up and establishment of these beneficial microbes in the rhizosphere zone.KeywordsAntagonistParasitismRhizospherePopulation dynamicsAbiotic stressPlant growthPlant Biomass

In this study, plant growth promoting rhizobacteria (PGPR) and plant growth promoting fungi (PGPF) were isolated from soil adhered to the roots of herbs. PGPR and PGPF isolates were selected for producing microbial inoculant as a starter culture for bio-fertilizer production. The screening of PGPR and PGPF was performed using the spread plate technique on the selected medium. Total plant growth promoting microorganisms (PGPM) were composed of 72 isolates, nitrogen-fixing microorganisms: 39 isolates, phosphate-solubilizing: 11 isolates, and potassium-solubilizing: 22 isolates. Two bacterial isolates, S-K7-2 and S-P7-1, had the highest plant growth promoting abilities, and a fungus isolate, Di-K7-2, was able to produce the greatest amount of IAA, which was 45.17 μg IAA equivalent/ml. The isolates were tested on hairy basil seed germination. Treatment using microbial cell dissolved in sterile distilled water had the greatest potential for stimulating the growth of seed and presented 145.26% of GI, followed by 82.87% where the treatment was with IAA standard. The study of the effect of PGPR and PGPF on hairy basil growth found that the highest biomass was shown in treatment 3, peat supplemented bacteria (S-K7-2, S-P7-1), which indicated that rhizobacteria immobilized on peat was able to enhance the growth of hairy basil and had better potential for promoting plant development compared with chemical fertilizer treatment.

Warhorses in soil bioremediation: Seed biopriming with PGPF secretome to phytostimulate crop health under heavy metal stress

Plant growth-promoting fungi (PGPF) constitute diverse genera of nonpathogenic fungi that provide a variety of benefits to their host plants. PGPF show an effective role in sustainable agriculture. Meeting increasing demand for crop production without damage to the environment is the biggest challenge nowadays. The use of PGPF has been recognized as an environmentally friendly way of increasing crop production. These fungi have proven to increase crop yields by improving germination, seedling vigor, plant growth, root morphogenesis, photosynthesis, and flowering through either a direct or indirect mechanism. The mechanisms of PGPF involve solubilizing and mineralizing nutrients for easy uptake by plants, regulating hormonal balance, producing volatile organic compounds and microbial enzyme, suppressing plant pathogens and ameliorating abiotic stresses. Successful colonization is an intrinsic factor for most PGPF to exert their beneficial effects on plants. A certain level of specificity exists in the interactions between plant species and PGPF for root colonization and growth promoting effects. There is a gap between the number of reported efficacious PGPF and the number of PGPF as biofertilizer. Efforts should be strengthened to improve the efficacy and commercialization of PGPF. Hence, this chapter summarizes valuable information regarding the application and mechanisms of PGPF in sustainable agriculture.

Apple replant disease (ARD) can increase apple tree ( Malus domestica Borkh) mortality, delay production, and reduce yield, resulting in losses of up to $60 K/ha over an orchard’s lifespan. Common fumigation treatments can harm human and environmental health, have variable effectiveness, and disrupt beneficial soil microbial activity and processes. An experiment was conducted at the Simcoe Research Station in Norfolk County, Ontario to assess the effectiveness of commercially available plant growth-promoting (PGP) microbial biocontrols to treat ARD. Five treatments were replicated in-field five times as a randomized block design. Treatments included: untreated control, fumigation control (chloropicrin (FC)), PGP fungi (PGP-F), PGP rhizobacteria (PGP-R), and a combination of PGP-F and PGP-R (PGP-M). Trees growth and health and rhizosphere microbial diversity was assessed at three points over 2 years. PGP-R produced the greatest mean root mass followed by the chemical fumigation, which was 32% and 10% more root mass than the untreated control, respectively. Chemical fumigation resulted in the greatest above-ground biomass tree growth followed by the PGP-R, accumulating 30% and 6% more biomass than the untreated control. However, PGP-F accumulated less biomass than the untreated control. FC and PGP-R both resulted in strong growth but impacted the microbial community differently. PGP-R increased rhizosphere bacterial diversity and decreased fungal diversity while FC did the opposite. PGP-R changes to bacterial communities persisted while FC soils resembled the untreated control most closely after two years. These results indicate PGP-R biocontrol treatments are viable alternatives to fumigation for apple growers facing ARD.

This groundbreaking study ventures into uncharted territory to explore the vast potential of Plant Growth Promoting Fungi (PGPF) as multifaceted allies in agricultural sustainability. Departing from traditional paradigms, the research sets out to identify and characterize non-pathogenic fungal isolates with the capacity to serve as potent PGPF agents. Employing a pioneering approach, fungal isolates are meticulously collected from the rhizosphere of plants, heralding a new era of ecological exploration at the microorganism level. Rigorous testing for pathogenicity on soybean seeds unveils a rich reservoir of fungi diversity, with 18 isolates demonstrating remarkable efficacy in enhancing germination rates and promoting vigorous seedling growth. These findings not only underscore the pivotal role of PGPF in bolstering plant health and resilience but also herald a paradigm shift in sustainable agriculture. With the potential to serve as biopesticides for plant protection and biofertilizers for enhancing growth, these PGPF isolates offer a promising avenue for reducing reliance on synthetic inputs and mitigating environmental impacts. Moreover, their integration into integrated disease management strategies holds the promise of synergistic efficacy, paving the way for holistic approaches to agricultural sustainability. This research not only expands the frontiers of knowledge surrounding PGPF but also lays the groundwork for transformative innovations in agroecological practices, ushering in a greener, more resilient future for global agriculture.

Soil is one of the main habitats of fungi and bacteria, and their interactions with the host plant help and promote plant growth and productivity in agriculture. Agronomists and environmentalists are focussing on sustainably managing the agroecosystem by using plant growth-promoting microbes (PGPM). They include bacteria called plant growth-promoting rhizobacteria (PGPR) and fungi referred to as plant growth-promoting fungi (PGPF). Plant growth-promoting fungi (PGPF) are nonpathogenic soil-borne fungi that establish a positive interaction with plants in the rhizosphere. PGPF can improve crop productivity by improving seed germination vigour root and shoot morphogenesis, and flowering through direct or indirect mechanisms, which include solubilizing nutrients, regulating hormones, producing enzymes, organic compounds, resistance to abiotic stress, and suppressing phytopathogens. The utilization of PGPF can be considered an eco-friendly method of improving crop production. The potential effective microbes may also be added in the form of biopesticides and biofertilizers promoting the growth of plants. The use of new biotechnological tools to aid genetic engineering of the PGPF has resulted in genetic transformation and overexpression of synergistic action of one or more traits, which could enhance plant growth, confer improved crop benefits, and produce sustainable yield. The chapter describes the diversity of PGPF found in the soil and their role in promoting plant growth and yield. The chapter also discusses the various mechanisms of PGPF interactions with plants and their beneficial roles in promoting crop productivity leading to sustainable agriculture.

The demand for a more sustainable agriculture, coupled with the need for optimized crop productivity, has driven the use of microorganisms for the biocontrol of diseases and pests, as well as for growth promotion. The use of plant growth-promoting rhizobacteria (PGPR) and plant growth-promoting fungi (PGPF) in Brazilian production systems has become increasingly common, with the number of microbial inoculant registrations in the country growing every year. PGPR and PGPF occupy various niches in the rhizosphere, playing a crucial role in soil nutrient cycling, as well as influencing various plant physiological processes. In this review, we address the main mechanisms used by these microbial agents in growth promotion and the use of strain co-inoculation as a strategy to enhance the efficacy of these products. Subsequently, we conduct an analysis of the available inoculants in Brazil, detailing the microorganisms available for the main Brazilian crops, and the prospects of this market regarding research and development of new products for the coming years based on the current challenges faced.

Plant growth-promoting rhizobacteria (PGPR), plant growth-promoting fungi (PGPF), and their interactions play an important role in the biological control of soil populations and plant pests. PGPR/PGPF produce a wide range of bioactive compounds such as siderophores, enzymes, and other compounds with low molecular weight that play an important role in the ecological strategy in the competition for space and nutrients. The PGPR/PGPF can also induce the induced systemic resistance (ISR) in the plants. Thus, the bioprospecting of microorganisms as potential antagonists of plant pathogens is one of the currently studied alternatives studied to control crop diseases. In this chapter, we reviewed several PGPR/PGPF and how they are used to control pathogens in plants.

It is unanimously admitted that the chemical fertilizers and pesticides used in modern agriculture create a real environmental and public health problems. One of the promising solutions to substitute these agrochemicals products is the use of bio-resources, including plant growth promoting rhizobacteria (PGPR). The PGPR focused more and more scientific attention in recent decades. These rhizospheric bacteria colonize actively the root system of plants and improve their growth and yield. The PGPR use different mechanisms of action to promote plant growth. These mechanisms were grouped into three clusters according to the PGPR effects on plant physiology. These groups are as follow: (i) biofertilization including biological fixation of atmospheric nitrogen, phosphate solubilization, siderophores production and exopolysaccharides production; (ii) phytostimulation including production of indole acetic acid, gibberellins, cytokinins and ethylene; and (ii) biocontrol including induction of systemic resistance, competition for iron, nutrient and space, production of antibiotics, lytic enzymes, hydrogen cyanide and volatile compounds. In view of the latest advances in PGPR biotechnology, this paper proposes to do the review on PGPR in rhizosphere and describes the different mechanisms used by PGPR to promote the plants growth and health. In prospect to a healthy and sustainable agriculture, respectful of environment, the PGPR approach revealed as one of the best alternatives. Key words: Rhizosphere, plant growth promoting rhizobacteria (PGPR), root colonization, biofertilization, biocontrol, biostimulation, interaction plant-microorganisms, sustainable agriculture.

Background: This study is about finding plant growth-promoting fungi (PGPF) that can resist fluoride, which is important for sustainable farming, especially in areas with fluoride contamination. Fluoride is commonly found in water and soil and it can harm plant health and agricultural productivity. Some fungi have developed ways to grow in high-fluoride conditions, helping plants grow and aiding in cleaning up the environment. We focused on identifying useful PGPF from the soil around plant roots, which is known for having many diverse microbes. Method: We tested the successful fungi isolates for their PGPF capabilities by using PCR to amplify the Internal Transcribed Spacer (ITS) region, a commonly used technique for identifying different fungal species. After amplifying the DNA, we sequenced the PCR products and analyzed the sequences using the BLAST database to identify the species. Result: Our research identified important fluoride-tolerant PGPF species, including Aspergillus flavus, Aspergillus niger, Cladosporium cladosporioides and Penicillium chrysogenum. These fungi showed abilities such as breaking down phosphate, producing growth hormones and stopping pathogens in high fluoride conditions. Adding these PGPF to farming practices has the potential to create strong fungal inoculants that can boost crop growth and productivity in areas affected by fluoride. Overall, this study lays the groundwork for more research and field tests to confirm how these fungi can be used practically, which may help improve sustainable farming and food security.

The olive tree (Olea europaea L.) is an emblematic, long-living fruit tree species of profound economic and environmental importance. This study is a literature review of articles published during the last 10 years about the role of beneficial microbes [Arbuscular Mycorrhizal Fungi (AMF), Plant Growth Promoting Rhizobacteria (PGPR), Plant Growth Promoting Fungi (PGPF), and Endophytes] on olive tree plant growth and productivity, pathogen control, and alleviation from abiotic stress. The majority of the studies examined the AMF effect using mostly Rhizophagus irregularis and Glomus mosseae species. These AMF species stimulate the root growth improving the resistance of olive plants to environmental and transplantation stresses. Among the PGPR, the nitrogen-fixing bacteria Azospirillum sp. and potassium- and phosphorous-solubilizing Bacillus sp. species were studied extensively. These PGPR species were combined with proper cultural practices and improved considerably olive plant’s growth. The endophytic bacterial species Pseudomonas fluorescens and Bacillus sp., as well as the fungal species Trichoderma sp. were identified as the most effective biocontrol agents against olive tree diseases (e.g., Verticillium wilt, root rot, and anthracnose).

Global climatic change has resulted in the increased activity of biotic and abiotic stresses on the agricultural crops and forest ecosystem. To cope with stresses has now become crucial for nature’s survival. Biotic stress is referred to as the phytopathogens, while abiotic stress includes temperature, salinity, drought, and heavy metals in soil due to excessive use of sprays and chemical detergents. Apart from affecting the crop yield, it also affects the bioremediation efficiency and ecosystems of forests. In this case, agronomists and agriculturalists are looking toward the use of plant growth-promoting microbes (plant growth-promoting rhizobacteria (PGPRs), plant growth-promoting bacteria (PGPB), and plant growth-promoting fungi (PGPF)) for better production and health of plants. This way is environmentally friendly, effective, and sustainable as compared to the conventional system, i.e., pesticides and chemical fertilizers. Plant–microbe interaction increases the survival of plants by minimizing the negative effects of biotic and abiotic stresses. The use of “Omics and bio-formulations” is the recent achievements made in this sector by considering future concerns against biotic and abiotic stress-causing factors.KeywordsBioremediationBiotic and abiotic stressesDroughtPlant growth-promoting hormonesSalinity