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Microbial Applications for Sustainable Agriculture
Abstract
Agriculture in the current era is highly dependent on chemical fertilizers, pesticides and weedicides. Excessive applications of these chemicals on crop plants has increased the production cost, jeopardized the environment and has depleted the non-renewable resources. Potential threats to non-renewable resources and soil, water, air environments have led to seek alternative approaches for sustainable crop production and clean environment. To lessen these adversaries, not only scientific community, but industry and farmers are also continuously involved in research, development and adoption of new sustainable technologies. The tiny organisms in rhizosphere have shown their potential to play ubiquitous role in sustainable agricultural development and have been in continuous use since over the last century. In this chapter, different aspects of microbial applications for sustainable agriculture are elaborated. Applications of bacteria-containing biofertilizers, their types and benefits to crops have been discussed. Reports on plant growth promotion through phytohormones, siderophores and enzymes production by rhizobacteria are also detailed. Moreover, sustainable control of plant diseases through biocontrol and amelioration of abiotic stresses including; drought, salinity, climate change and heavy metals by using rhizobacteria are also encompassed in this chapter.
... Associative Nitrogen Fixers of roots or inside the root (in intercellular spaces). Species of Azospirillum are a peculiar example of such species which form an association with important cereal crops such as rice, wheat, corn, oats, and barley (Afzal and Asad, 2019). It is an Associative bacterium that helps stimulate plant growth by producing hormones such as IAA and gibberellins. ...
... Meanwhile, soil microstructures including fungi, bacteria, and actinomycetes are able to destroy the crystal structure of minerals and release trapped potassium in its structure (Nazli et al., 2020). There are reports of the influence of soil microbial community including mycorrhizal fungi, and other fungi as well as soil bacteria such as Pseudomonas, Bacillus, Rhizobium, and Micrococcus on the release of potassium from soil sources (Afzal and Asad, 2019). However, in most studies, the effect of B. mucilaginosus on the potassium nutrition of various plants has been mentioned (Nazli et al., 2020). ...
... Auxins aid in adventitious roots penetration thus providing additional nutrients for bacterial and plant growth. These characteristics make auxins an important metabolite to regulate plant-microbe interactions in terms of Phyto stabilization and pathogenicity (Afzal and Asad, 2019). Another vital phytohormone, Gibberellic acid (GA) plays a crucial role in alleviating the drought stress and in initiating flowering and for hypocotyls elongation (Shu et al., 2018)). ...
The increasing global human population and depletion of natural resources
of energy need a sustainable supply of food and energy without causing
any risk to the environment. Currently, agriculture is highly dependent on
chemical fertilizers, pesticides, and weedicides. Excessive use of chemical
fertilizers will cause an imbalance of elements and nutrients in the soil,
reduce the yield of agricultural products, increase the production costs and
endanger the health of humans and other living organisms. The potential
threats to non-renewable resources and soil, water, and air environments
have led scientists to seek alternative approaches that involve the use of
biological fertilizers that are driven by bacteria, fungi, algae, or other soil
organisms. Biofertilizers not only have many economic and environmental
benefits but also, could boost the adequate supply of nutrients to the host
plants and guarantee their suitable development and regulation of their physiology. In order to achieve sustainable development in agriculture and
to meet the nutritional needs of plants, the use of biological fertilizers can
be an effective solution. In this chapter, we provide details on different
aspects of microbial applications that can help in developing sustainable
farming practices. Applications of bacteria-containing biofertilizers, their
variations, the challenges and benefits to crops have been discussed. The
results of several studies on plant growth promotion through phytohormones,
siderophores, and enzyme production by rhizobacteria are also presented.
Moreover, possible benefits of genetically modified microorganisms and
also their possible environmental effects related to diverse agricultural
environments with an emphasis on GM PGPRs (biofertilizers) and GM
microbial agents used as biopesticides, and amelioration of abiotic stresses
such as; temperature, drought, pH, salinity, availability of nutrients, and
heavy metals by using Cyanobacterial NS rhizobacteria and their role in
sustainable agriculture and production of products with desirable quality
are also encompassed in this chapter.
... Associative Nitrogen Fixers of roots or inside the root (in intercellular spaces). Species of Azospirillum are a peculiar example of such species which form an association with important cereal crops such as rice, wheat, corn, oats, and barley (Afzal and Asad, 2019). It is an Associative bacterium that helps stimulate plant growth by producing hormones such as IAA and gibberellins. ...
... Meanwhile, soil microstructures including fungi, bacteria, and actinomycetes are able to destroy the crystal structure of minerals and release trapped potassium in its structure (Nazli et al., 2020). There are reports of the influence of soil microbial community including mycorrhizal fungi, and other fungi as well as soil bacteria such as Pseudomonas, Bacillus, Rhizobium, and Micrococcus on the release of potassium from soil sources (Afzal and Asad, 2019). However, in most studies, the effect of B. mucilaginosus on the potassium nutrition of various plants has been mentioned (Nazli et al., 2020). ...
... Auxins aid in adventitious roots penetration thus providing additional nutrients for bacterial and plant growth. These characteristics make auxins an important metabolite to regulate plant-microbe interactions in terms of Phyto stabilization and pathogenicity (Afzal and Asad, 2019). Another vital phytohormone, Gibberellic acid (GA) plays a crucial role in alleviating the drought stress and in initiating flowering and for hypocotyls elongation (Shu et al., 2018)). ...
By 2050 the world’s population will reach 9 billion. Moreover, land and water
resources are dwindling, and so there is an urgent need to find solutions for
food security and sustainable agriculture. Furthermore, the challenge to
produce more food for an increasing global population on reducing agricultural
land severely threatens crop productivity. Because of rising global warming,
large portions of fields, crops are adversely affected by several environmental
restrictions like cold, salt, heat and drought stress. The frequency and intensity
of abiotic stresses have increased due to the global climate change and
these stresses can have a significant effect on crop yield. Abiotic stress is the main restriction in sustainable agriculture. It is indispensable to focus on
innovative breeding technology that can help in understanding and improving
stress tolerance. In this regard, the use of genetic engineering or biotechnology
to improve abiotic stress tolerance are necessary to curtail yield losses. For
sustainable crop production in the future, it is critical to develop varieties
with improved stress tolerance. Plant genetic resources have played a key
role in this process. Through evolution plants have evolved a complex
regulatory network of genetic machinery which includes transcription factors,
small RNAs, signaling pathways, stress sensors and defense pathways. Thus,
to develop stress tolerant plants, it is important to identify and characterize
vital genes involved in abiotic stress tolerance. Moreover, the progress in
genome editing technologies (GETs) and availability of fully sequenced
genome of many crops has helped scientists to edit around any attribute of
interest. Genome editing using artificial nucleases like zinc-finger nucleases
(ZFNs), transcription activator-like effector nucleases (TALENS), and
Clustered regulatory Interspaced Short Palindromic Repeat (CRISPR), has
considerably wedged basic similarly as applied analysis as well as plant
breeding by fast the editing of target genome in a precise and foreseeable
manner. This chapter focuses on the latest biotechnological ways to improve
abiotic stress tolerance in plants.
... Other alternative solutions are emerging, particularly biobased ones in the circular economy context, as compiled recently by Chojnacka et al. (2020Chojnacka et al. ( , 2022. They consist of reactivating agricultural soils (i) by stimulating the activity of beneficial microorganisms in situ, to improve nutrient availability and ameliorate soil structure by favoring aggregate formation (Rashid et al. 2016), or (ii) by introducing microorganisms previously selected for their direct beneficial effect on plant growth and development (Afzal and Asad 2019;Hartmann and Six 2023). The latter can be applied as commercial products of single or determined mixed strains (Parnell et al. 2016). ...
Fermented forest litter (FFL) is a bioproduct used as biofertilizer for several decades in Eastern Asia and Latin America. It is locally handcrafted by farmers in anaerobic conditions by fermenting forest litter added with agricultural by-products such as whey, cereal bran, and molasses. The aim of this study was to characterize the FFL process and product through gas and liquid chromatography analyses. It also provides some highlights on the influence of O2 on this solid-state culture. Under anoxic condition, a maximum CO2 production rate (CDPR) of 0.41 mL/h∙g dry matter (dm) was reached after 8 days. The main volatile organic compounds (VOCs) were ethanol and ethyl acetate, with a production rate profile similar to CDPR. After 21 days of culture, no residual sucrose nor lactose was detected. Lactic and acetic acids reached 58.8 mg/g dm and 10.2 mg/g dm, respectively, ensuring the acidification of the matrix to a final pH of 4.72. A metabarcoding analysis revealed that heterolactic acid bacteria (Lentilactobacillus, Leuconostoc), homolactic acid bacteria (Lactococcus), and yeasts (Saccharomyces, Clavispora) were predominant. Predicted genes in the microbiome confirmed the potential link between detected bacteria and acids and VOCs produced. When O2 was fed to the cultures, final pH reached values up to 8.5. No significant amounts of lactic nor acetic acid were found. In addition, a strong shift in microbial communities was observed, with a predominance of Proteobacteria and molds, among which are potential pathogens like Fusarium species. This suggests that particular care must be brought to maintain anoxic conditions throughout the process.
... In addition, compost along with rhizobacteria and N-fertilizer may also improve growth and yield of crops The rhizosphere, volume of soil surrounding roots and influenced chemically, physically and biologically by the plant root, is a highly favorable habitat for the proliferation of microorganisms and exerts a potential impact on plant health and soil fertility (Brahmaprakash et al., 2017). Soil microorganisms are considered a potential and economical source of auxin production released as secondary metabolites, which may have pronounced effects on plant growth and development (Afzal and Asad, 2019). ...
... Aztobacter chroonocum isolated from saline soil can produced gibberellins in plants (Hindersah et al., 2019). Afzal & Asad, (2019) have been reported that biofertilizers containing Rhizobium, Aztobacter, Pseudomonas sp., has ability to produced phytohormones including IAA, GA and ABA is growth inhibiting hormone produced under stress conditions (Takahashi & Shinozaki, 2019). Fig. 2(e) showed that all the treatments showed reduced production of ABA as compared to control but biofertilizer of A. chroococum and P. chinense was inhibitorier to ABA production as compared to control. ...
The quest for enhancing agricultural yields due to increased pressure on food production has inevitably led to the
indiscriminate use of chemical fertilizers and other agrochemicals. The potential role of plant growth promoting
rhizobacteria (PGPR) as a biofertilizer evolved as appropriate substitute to neutralize adverse environmental impacts
wielded by manmade agrochemicals. The recent study was conducted to elucidate the role of plant growth promoting
rhizobacteria as biofertilizer. Maize seeds were treated with PGPR (Azotobacter chroococum & Planomicrobium chinense)
and in combination to observe the effects on physiology, hormonal activity, antioxidant enzymes, nutritional composition,
and productivity. The study revealed that application of PGPRs and biofertilizer significantly (p<0.05) improved the physio�biochemical attributes including root length (222%), shoot length (85.1%), proline (%), phenolics (71%), flavonoids (85%)
and protein (94%) as compared to control. The hormonal activity and plant-defense related antioxidant enzymes activities
also improved leading to improve the yield, the observed increased in grain yield (81%) with 100 grain weight 25.37%. The
application of PGPR resulted in increased soil fertility, maximum increase in soil organic matter (26.74%), total nitrogen
(33.10%), available phosphorus (99.17%) and available potassium (48.55%). Similarly maximum increase in nitrogen was
54.4%, phosphorus 54.5%, potassium 34.72%, magnesium 78%, was observed. The present study clearly signifies that the
use of biofertilizers and bioinoculants for sustainable yield production of maize is environment friendly and can used as
alternative of the chemical fertilizers.
Present investigation was aimed to isolate and characterize plant growth promoting rhizobacteria (Rhizobia) from rhizosphere (EC: 2300 µS/cm; pH: 8.6) of four halophytes: Sonchus arvensis L., (sow thistle), Solanum surratense Burm. F., (yellow berried night shade), Lactuca dissecta D. Don., (wild lettuce) and Chrysopogon aucheri (Boiss.) Stapf (golden beared grass) collected from Khewra Salt Range and compared with Rhizobium isolate from Solanum surratense Burm. F. of arid soil (EC: 210 µS/cm; pH: 7.9) of Attock (treated as control). The isolates were identified and characterized on the basis of colony morphology and biochemical traits viz gram staining, catalase and oxidase tests and carbon and nitrogen source utilization pattern. The survival efficiency of isolates was measured in culture (colony forming unit / g soil). The genetic diversity among the isolates assessed by RAPD-DNA finger printing and PCR was done for the presence of 16S-rRNA gene. On the basis of carbon / nitrogen source utilization patterns, Rhizobium isolates placed in five different groups and were designated as Rkh1, Rkh2, Rkh3, Rkh4 and Rak5 but RAPD tests categorized the isolates into two clusters. The RAPD results were further analyzed by MVSP software; similarity matrix was measured and converted into dendrogram using UPGMA clustering method.
Associative N fixation (ANF), the process by which dinitrogen gas is converted to ammonia by bacteria in casual association with plants, has not been well-studied in temperate ecosystems. We examined the ANF potential of switchgrass (Panicum virgatum L.), a North American prairie grass whose productivity is often unresponsive to N fertilizer addition, via separate short-term ¹⁵N2 incubations of rhizosphere soils and excised roots four times during the growing season. Measurements occurred along N fertilization gradients at two sites with contrasting soil fertility (Wisconsin, USA Mollisols and Michigan, USA Alfisols). In general, we found that ANF potentials declined with long-term N addition, corresponding with increased soil N availability. Although we hypothesized that ANF potential would track plant N demand through the growing season, the highest root fixation rates occurred after plants senesced, suggesting that root diazotrophs exploit carbon (C) released during senescence, as C is translocated from aboveground tissues to roots for wintertime storage. Measured ANF potentials, coupled with mass balance calculations, suggest that ANF appears to be an important source of N to unfertilized switchgrass, and, by extension, to temperate grasslands in general.
Several anthropogenic activities including mining, modern agricultural practices, and industrialization have long-term detrimental effect on our environment. All these factors lead to increase in heavy metal concentration in soil, water, and air. Soil contamination with heavy metals cause several environmental problems and imparts toxic effect on plant as well as animals. In response to these adverse conditions, plants evolve complex molecular and physiological mechanisms for better adaptability, tolerance, and survival. Nowadays conventional breeding and transgenic technology are being used for development of metal stress resistant varieties which, however, are time consuming and labor intensive. Interestingly the use of microbes as an alternate technology for improving metal tolerance of plants is gaining momentum recently. The use of these beneficial microorganisms is considered as one of the most promising methods for safe crop-management practices. Interaction of plants with soil microorganisms can play a vital role in acclimatizing plants to metalliferous environments, and can thus be explored to improve microbe-assisted metal tolerance. Plant-associated microbes decrease metal accumulation in plant tissues and also help to reduce metal bioavailability in soil through various mechanisms. Nowadays, a novel phytobacterial strategy, i.e., genetically transformed bacteria has been used to increase remediation of heavy metals and stress tolerance in plants. This review takes into account our current state of knowledge of the harmful effects of heavy metal stress, the signaling responses to metal stress, and the role of plant-associated microbes in metal stress tolerance. The review also highlights the challenges and opportunities in this continued area of research on plant–microbe–metal interaction.
The application of microbial inoculants (biofertilizers) is a promising technology for future sustainable farming systems in view of rapidly decreasing phosphorus stocks and the need to more efficiently use available nitrogen (N). Various microbial taxa are currently used as biofertilizers, based on their capacity to access nutrients from fertilizers and soil stocks, to fix atmospheric nitrogen, to improve water uptake or to act as biocontrol agents. Despite the existence of a considerable knowledge on effects of specific taxa of biofertilizers, a comprehensive quantitative assessment of the performance of biofertilizers with different traits such as phosphorus solubilization and N fixation applied to various crops at a global scale is missing. We conducted a meta-analysis to quantify benefits of biofertilizers in terms of yield increase, nitrogen and phosphorus use efficiency, based on 171 peer reviewed publications that met eligibility criteria. Major findings are: (i) the superiority of biofertilizer performance in dry climates over other climatic regions (yield response: dry climate +20.0 ± 1.7%, tropical climate +14.9 ± 1.2%, oceanic climate +10.0 ± 3.7%, continental climate +8.5 ± 2.4%); (ii) meta-regression analyses revealed that yield response due to biofertilizer application was generally small at low soil P levels; efficacy increased along higher soil P levels in the order arbuscular mycorrhizal fungi (AMF), P solubilizers, and N fixers; (iii) meta-regressions showed that the success of inoculation with AMF was greater at low organic matter content and at neutral pH. Our comprehensive analysis provides a basis and guidance for proper choice and application of biofertilizers.
The most common, devastating problem in agriculture is plant (pathogenic) diseases and abiotic conditions which have a profound effect on growth and yield of the plant resulting in heavy losses. In order to prevent losses, different chemicals are used indiscriminately, which in turn lead to environmental pollution due to their persistence and toxicity yet employed to meet consumer demand. To fight ever increasing demand and indiscriminate use of chemical agents along with their devastating after effects in agriculture, we need less invasive, eco-friendly and most importantly sustainable practices. Plant growth promoting rhizobacteria (PGPR) influence different physiological activities of the plant through various mechanisms (metabolites, antibiotics, Induced Systemic Resistance and enzymes) and impart protection from pathogens as well as environmental stress factors. But, current applications are limited in this regard as mechanisms involved, field applications variance and lack of farmer awareness contributing majorly. Current review tries to provide comprehensive knowledge on the PGPR’s applications as plant protectant against pathogens & abiotic factors leading to sustainable agricultural practices.
Frankia strains are N2-fixing actinomycetes whose isolation and cultivation were first reported in 1978. They induce N2-fixing root nodules on diverse nonleguminous (actinorhizal) plants that are important in ecological successions and in land reclamation and remediation. The genus Frankia encompasses a diverse group of soil actinomycetes that have in common the formation of multilocular sporangia, filamentous growth, and nitrogenase-containing vesicles enveloped in multilaminated lipid envelopes. The relatively constant morphology of vesicles in culture is modified by plant interactions in symbiosis to give a diverse array of vesicles shapes. Recent studies of the genetics and molecular genetics of these organisms have begun to provide new insights into higher-plant-bacterium interactions that lead to productive N2-fixing symbioses. Sufficient information about the relationship of Frankia strains to other bacteria, and to each other, is now available to warrant the creation of some species based on phenotypic and genetic criteria.
The majority of genes encoding gibberellin (GA) biosynthesis and deactivation enzymes have been identified to date. Recent studies have highlighted the occurrence of previously unrecognized deactivation mechanisms, including epoxidation and methylation. GA concentrations in plant tissues are carefully optimized by a number of internal and external signals. Studies have recently shown that, in many cases, bioactive GA levels are modulated through coordinated regulation of GA biosynthesis and deactivation. In addition, the identification of transcription factors that directly regulate GA biosynthesis and deactivation genes has started to uncover the molecular mechanisms for fine-tuning the hormone levels. In this article, I summarize our current understanding of the GA biosynthesis and deactivation pathways in plants, and discuss how the concentration of bioactive GAs is regulated in several selected systems.
A translated book from English to Arabic, covering all topics related to the training and development functionز
Among various toxic heavy metals (HMs), Cadmium (Cd) and Chromium (Cr) have proven to be extremely noxious for environment, hence warranting their remediation. Current study investigated the plant growth promoting rhizobacteria (PGPR) assisted Cd and Cr removal by Brassica oleraceae under controlled environment. For this purpose, B. oleraceae plants were grown at different concentration of Cd (4, 10 mg kg⁻¹) and Cr (35, 50 mg kg⁻¹) and inoculated with strains evaluated for PGPR characteristics. For heavy metals and growth hormone production experiments, two strains, HRS-C3 and B6 were used. Inoculation with PGPRs significantly increased the fresh and dry biomass of plant shoots as compared to un-inoculated counterparts. Under heavy metal stress conditions, inoculation with HRS-C3 increased the fresh biomass of plants from 535.08 to 657.66 mg and corresponding dry weight from 214.50 to 295.30 mg compared to un-inoculated plants under stressed conditions. Interestingly, PGPRs treatment increased the Cd uptake by plant, while Cr accumulation was significantly reduced in inoculated plants as compared to un-inoculated plants. PGPR strain, HRS-C3 has proved to be more efficient than B6 with reference to growth hormones (IAA and GA) production. Inoculation with mix culture of both strains, HRS-C3 and B6 produced significantly higher concentrations of IAA and GA than singular applications. Overall, PGPRs enhanced Cd availability to plant by reducing stress to tested plants. This phenomenon suggests that microbes played a key role for remediation of medium level contamination of Cd by B. oleraceae in contaminated soil. However, the results of same strains indicated that Cr uptake was reduced in B. oleraceae. Results suggest that there is need to employ metal specific strains for Cr remediation.
Two root-associated bacteria, one identified as rhizospheric Bacillus megaterium and the other as endophytic Pseudomonas aeruginosa, were isolated from the rhizosphere soil and root of Suaeda nudiflora wild mosque plant, respectively. The effects of these two bacteria were studied alone and in combination on sugar metabolism for plant growth and development. Soluble sugars in the plant downregulate photosynthesis, resulting in reduced plant growth, but inoculation with root-associated bacteria enhanced plant growth by enhancing photosynthesis. Sugars, owing to their regulatory function, affect all phases of the life cycle of both the plants and bacteria. Inoculation with root-associated bacteria improves sugar accumulation in inoculated plants and it also influences the programmed cell death under biotic stress. Accumulation of soluble sugar has also been observed in inoculated plant under abiotic stress and acts as osmoprotectant. The isolates also induced the differential expression of stress-related gene RAB18 in maize plants during RNA profiling. The results indicate that the ecofriendly root-associated bacteria can serve as a simple and cheap tool for regulating sugar concentration in plant and combating stress in crops as well as for increased productivity because of its growth promoting ability.