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PGPR‐mediated induction of systemic resistance and physiochemical alterations in plants against the pathogens: Current perspectives
Abstract
Plant growth‐promoting rhizobacteria (PGPR) are diverse groups of plant‐associated microorganisms, which can reduce the severity or incidence of disease during antagonism among bacteria and soil‐borne pathogens, as well as by influencing a systemic resistance to elicit defense response in host plants. An amalgamation of various strains of PGPR has improved the efficacy by enhancing the systemic resistance opposed to various pathogens affecting the crop. Many PGPR used with seed treatment causes structural improvement of the cell wall and physiological/biochemical changes leading to the synthesis of proteins, peptides, and chemicals occupied in plant defense mechanisms. The major determinants of PGPR‐mediated induced systemic resistance (ISR) are lipopolysaccharides, lipopeptides, siderophores, pyocyanin, antibiotics 2,4‐diacetylphoroglucinol, the volatile 2,3‐butanediol, N‐alkylated benzylamine, and iron‐regulated compounds. Many PGPR inoculants have been commercialized and these inoculants consequently aid in the improvement of crop growth yield and provide effective reinforcement to the crop from disease, whereas other inoculants are used as biofertilizers for native as well as crops growing at diverse extreme habitat and exhibit multifunctional plant growth‐promoting attributes. A number of applications of PGPR formulation are needed to maintain the resistance levels in crop plants. Several microarray‐based studies have been done to identify the genes, which are associated with PGPR‐induced systemic resistance. Identification of these genes associated with ISR‐mediating disease suppression and biochemical changes in the crop plant is one of the essential steps in understanding the disease resistance mechanisms in crops. Therefore, in this review, we discuss the PGPR‐mediated innovative methods, focusing on the mode of action of compounds authorized that may be significant in the development contributing to enhance plant growth, disease resistance, and serve as an efficient bioinoculants for sustainable agriculture. The review also highlights current research progress in this field with a special emphasis on challenges, limitations, and their environmental and economic advantages.
... In contrast, those processes that protect plants against infection or allow plants to grow properly under stressful conditions are termed indirect mechanics (Goswami et al., 2016). Direct mechanisms comprise the potential to nitrogen-fix, solubilize insoluble phosphate, sequester iron, and generate phytohormones (including auxins, cytokinins, and gibberellins), while the capacity to synthesize antibiotics, enzymes, or to generate systemic resistance within plants are examples of indirect mechanisms (Gouda et al., 2018;Meena et al., 2020). ...
Plant Growth Promoting Rhizobacteria (PGPR) are rhizosphere-dwelling microorganisms which hold a great deal of potential for both plant growth stimulation and disease prevention. The characterization of PGPR will aid in the advancement and deployment of biocontrol agents. In this present work, rhizospheric soils were collected from several locations of Sylhet Agricultural University in order to obtain plant growth promoting rhizobacteria. Nineteen bacterial samples were extracted from a variety of fifteen distinct vegetable crops, viz. tomato, brinjal, beans, okra, cabbage, cauliflower, pumpkin, amaranth, malabar spinach, bitter gourd, ridge gourd, spiny gourd, sponge gourd, wax gourd, and snake gourd. These isolates were examined morphologically, biochemically, and screened for plant growth stimulating capability as well as their efficacy in combating the plant pathogen Fusarium oxysporum through antifungal activity. Among the isolates, only Lysinibacillus macroides (RB2), Lysinibacillus fusiformis (RB6) and Acinetobacter baumannii (RB15 and RB17) showed antifungal and growth promotion potentials. Therefore, the present study indicates that the vegetable rhizosphere contains potential rhizobacteria which could be utilized to enhance plant development and reduce disease incidence on vegetable crops.
... It was suggested that the reason for this drop is increased defense enzyme activity in plants that were treated with microbes. More importantly, since microbes may emit chelating compounds like organic acids, iron-chelating compounds and other secondary metabolites, microorganisms have the potential to scavenge the ROS generated by plants under stressful conditions 25 . ...
Root Knot Nematode (Meloidogyne incognita) is a major agricultural pest that significantly reduces crop yield. This study investigates the nematicidal potential of Bradyrhizobium japonicum strain 11477 against M. incognita to regulate its pathogenicity in Solanum lycopersicum. Tomato seeds were treated with bacterial cells and supernatant, grown under controlled conditions and later infested with nematode juveniles (5J2/seedling). After 10 days, nematode infestation led to reduced seedling growth, lower root and shoot biomass and decreased photosynthetic pigments. It also triggered oxidative stress, as indicated by elevated stress markers. Enzymatic and non-enzymatic antioxidants along with phenolic compounds showed increased activity in response to nematode-induced stress. However, B. japonicum treatment significantly reduced gall formation, improved plant growth and enhanced biochemical and histochemical attributes. Rhizobacteria also alleviated stress indices, strengthened antioxidant defenses and increased metabolite production. Confocal microscopy revealed hydrogen peroxide localization, glutathione content and nuclear and membrane damage in root apices, correlating with plant defense responses. This study highlights B. japonicum as a potent biocontrol agent that enhances plant growth and resilience against M. incognita. Notably, this is the first report on the impact of a leguminous rhizobacterium on a non-leguminous tomato plant, providing new insights into its potential for sustainable pest management.
... Moreover, bacterial activity induces systemic responses in plants, enhancing their metal tolerance. This process, termed induced systemic resistance (ISR), involves the activation of plant defense mechanisms in response to bacterial colonization (Meena et al. 2020;Yu et al. 2022). ISR enables plants to respond more effectively to environmental stressors, including heavy metals. ...
Metal stress in plants poses a significant challenge to global agriculture, reducing crop productivity and threatening food security. While recent advancements in microbiology and bacteriology have revealed the potential of plant-associated microbes to alleviate heavy metal toxicity, practical applications remain constrained by knowledge gaps and environmental variability. This review critically examines the dynamic interactions between plants and microbes under metal stress, focusing on specific microbial communities and their multifaceted roles in reducing metal toxicity. Key bacterial mechanisms, including biofilm formation, metal sequestration, antioxidant production, and stress-related gene expression, are explored for their contributions to plant resilience. Additionally, we discuss the diverse strategies employed by bacteria, such as the production of siderophores, phytohormones, and extracellular polymeric substances (EPS), to enhance metal tolerance in plants. Special emphasis is placed on the contributions of rhizobacteria, endophytes, and other plant-growth-promoting bacteria (PGPB) in bioremediation and sustainable agriculture. The review also highlights challenges, such as the variability of microbial efficacy in different environmental contexts, and emphasizes the need for field-scale studies to validate laboratory findings. By integrating microbial insights with plant physiological responses, this review provides a critical framework for harnessing microbial interventions to combat metal stress and achieve sustainable agricultural practices in metal-contaminated environments.
... However, soil often lacks sufficient nitrogen, which can be addressed through the application of commercially available nitrogen fertilizers. Unfortunately, these fertilizers can result in substantial losses of urea-N or NO3-N due to volatilization, leaching, and other environmental factors, leading to pollution problems (Meena et al. 2020). ...
p>The objective of this study was to investigate the impact of combining different doses and application methods of biofertilizers on the growth and yield of lowland rice ( Oryza sativa L.) in West Java. The experiment was designed as a completely randomized factorial with two factors and three replications. The first factor included three different biofertilizer application methods, and the second factor consisted of five different biofertilizer doses. The use of high-fertility alluvial soil was favorable for rice growth when treated with biofertilizers. The interaction between the applied method and biofertilizer dosage had a significant impact on various growth parameters, such as plant height, tiller number, stem fresh weight (g), stem dry weight (g), leaf dry weight (g), panicle number per plant, filled grain number per plant, unfilled grain number per plant, and total grain weight (g). The application of 300 g per pot biofertilizer dose at planting time resulted in the highest filled grain weight per plant (58.6 g) and total grain weight per plant (65.1 g). However, while biofertilizers significantly enhanced rice plant growth, none of the four biofertilizer dose treatments were significant when compared to the control in any of the three application methods. Optimally dosed biofertilizers, when applied at proper planting time, can serve as an alternative approach to enhance rice growth and yield in alluvial soil. This eco-friendly technology has the potential to be integrated into field management practices.</p
... The importance of V. lecanii, which produces HCN in the fight against pathogens, as a safe and environmentally friendly alternative is shown in ul Islam et al. (2023). HCN is a substance that exhibits interest in a variety of natural forms and has antifungal properties in addition to its potent role in promoting plant defenses against infections (Meena et al., 2020;Costa et al., 2022;Dimkić et al., 2022). The nematodes are a threat to plant growth because the infection delays vegetative development and transfers nutrients from the soil into other parts of the plants' root systems (Hussain et al., 2023). ...
... The fungi are not required to be metabolically active for ISR induction since live and dead organisms can induce ISR depending on the fungalehost combination (Kamle et al., 2020). ISR induction involves various compounds, including cell wall preparations, antibiotics, purified lipopolysaccharides, flagella, and siderophores, lipopeptides, pyocyanin, antibiotics, 2,3-butanediol, 2,4-diacetyl phloroglucinol, N-alkylated benzylamine, and iron-regulated compounds (Leeman et al., 1995;Meena et al., 2020). Other metabolites that elicit ISR include enzymes, e.g., xylanase, cellulase, and polygalacturonase. ...
... [149,150] Furthermore, advancing our understanding of the complex interactions between PGPR, plants, and abiotic stressors is essential for optimizing their use in mitigating environmental stresses and enhancing crop resilience. [151][152][153][154] Elucidating the molecular mechanisms underlying PGPRmediated stress tolerance in plants, as well as the signaling pathways involved in plant-microbe interactions, will provide valuable insights into the factors driving the effectiveness of PGPR-based interventions [155][156][157][158] Integrating multi-omics approaches, including genomics, transcriptomics, proteomics, and metabolomics, offers a powerful tool for unraveling the intricacies of microbial-plant interactions and identifying key genetic determinants of stress tolerance in PGPR strains. Harnessing advances in omics technologies for targeted isolation and characterization of stress-tolerant PGPR will enable the development of tailored inoculants with enhanced efficacy and specificity for different environmental conditions and crop species. ...
Plant Growth-Promoting Rhizobacteria (PGPR) represent a promising avenue for sustainable agriculture, offering multifaceted benefits to plants, including enhanced growth, nutrient uptake, and stress tolerance. Abiotic stressors, such as drought, salinity, temperature extremes, and soil contamination, pose significant challenges to agricultural productivity and sustainability. In response, researchers have turned their attention to isolating PGPR from abiotic stressed regions, where microbial communities have evolved mechanisms to thrive under harsh environmental conditions. This review provides a comprehensive overview of the role of PGPR in mitigating abiotic stress in agriculture, with a focus on their isolation and characterization from stress-prone environments.
The introduction sets the stage by highlighting the importance of PGPR in sustainable agriculture and the adverse effects of abiotic stress on plant growth and productivity. We discuss the mechanisms by which abiotic stressors disrupt plant physiology and metabolism, underscoring the need for innovative strategies to enhance crop resilience in the face of climate change. The rationale for isolating PGPR from abiotic stressed regions is elucidated, emphasizing its practical implications for addressing global challenges in agriculture and food security.
This review examines methodologies for isolating stress-tolerant PGPR strains, factors influencing their abundance and diversity in abiotic stressed environments, and case studies demonstrating successful isolation and characterization efforts. We explore the applications of stress-tolerant PGPR in sustainable agriculture, including biofertilization, bioremediation, and crop protection, with a focus on real-world examples and field trials. Challenges and future directions in harnessing PGPR from abiotic stressed regions are discussed, highlighting the need for scalable solutions and interdisciplinary collaborations.
In conclusion, harnessing stress-tolerant PGPR from abiotic stressed regions holds great promise for sustainable agriculture, offering innovative solutions to mitigate the adverse effects of climate change on crop productivity and environmental sustainability. Through a comprehensive analysis of current research findings and future perspectives, this review aims to underscore the significance of PGPR- based strategies for sustainable development and food security in a changing climate.
Plant viruses pose a significant threat to global agriculture, leading to substantial crop losses that jeopardise food security and disrupt ecosystem stability. These viral infections often reprogramme plant metabolism, compromising key pathways critical for growth and defence. For instance, infections by cucumber mosaic virus alter amino acid and secondary metabolite biosynthesis, including flavonoid and phenylpropanoid pathways, thereby weakening plant defences. Similarly, tomato bushy stunt virus disrupts lipid metabolism by altering the synthesis and accumulation of sterols and phospholipids, which are essential for viral replication and compromise membrane integrity. Recent advancements in gene‐editing technologies, such as CRISPR/Cas9, and metabolomics offer innovative strategies to mitigate these impacts. Precise genetic modifications can restore or optimise disrupted metabolic pathways, enhancing crop resilience to viral infections. Metabolomics further aids in identifying metabolic biomarkers linked to viral resistance, guiding breeding programmes aimed at developing virus‐resistant plants. By reducing the susceptibility of crops to viral infections, these approaches hold significant potential to reduce dependence on chemical pesticides, increase crop yields and promote sustainable agricultural practices. Future research should focus on expanding our understanding of virus–host interactions at the molecular level while exploring the long‐term ecological impacts of viral infections. Interdisciplinary approaches integrating multi‐omics technologies and sustainable management strategies will be critical in addressing the challenges posed by plant viruses and ensuring global agricultural stability.
Plant diseases caused by fungal pathogens pose a significant threat to global crop production, particularly in economically valuable crops like pepper and tomato. Biological control using microbial agents has emerged as a sustainable alternative to chemical fungicides, with Bacillus amyloliquefaciens PPL receiving attention for its potent antifungal activity. This review focuses on the cyclic lipopeptides (CLPs) produced by the B. amyloliquefaciens PPL strain, particularly the iturin and fengycin families. These CLPs play a crucial role in suppressing fungal pathogens, such as Colletotrichum (pepper anthracnose) and Fusarium oxysporum (tomato wilt), through membrane disruption and inhibition of fungal growth. Furthermore, we discuss the mechanisms underlying the antifungal activity of CLPs, the role of lecithin in enhancing production, and the potential of fengycin isoforms (F1, F2, F3) in disease management. Future perspectives on integrating B. amyloliquefaciens PPL and CLPs into sustainable agricultural practices are also presented.
Disease suppressive soils offer effective protection to plants against infection by soil-borne pathogens, including fungi, oomycetes, bacteria, and nematodes. The specific disease suppression that operates in these soils is, in most cases, microbial in origin. Therefore, suppressive soils are considered as a rich resource for the discovery of beneficial microorganisms with novel antimicrobial and other plant protective traits. To date, several microbial genera have been proposed as key players in disease suppressiveness of soils, but the complexity of the microbial interactions as well as the underlying mechanisms and microbial traits remain elusive for most disease suppressive soils. Recent developments in next generation sequencing and other ‘omics’ technologies have provided new insights into the microbial ecology of disease suppressive soils and the identification of microbial consortia and traits involved in disease suppressiveness. Here, we review the results of recent ‘omics’-based studies on the microbial basis of disease suppressive soils, with specific emphasis on the role of rhizosphere bacteria in this intriguing microbiological phenomenon.