Induced Systemic Resistance Research Articles

Bacillus velezensis CE 100 controls anthracnose disease in walnut trees (Juglans regia L.) by inhibiting Colletotrichum gloeosporioides and eliciting induced systemic resistance.

Biological control of plant diseases is recognized as an effective and environmental friendly alternative to chemical fungicides. We demonstrated the dual biocontrol strategy of Bacillus velezensis CE 100 through the hydrolytic activity of chitinase and β-1,3-glucanase and the elicitation of induced systemic resistance (ISR) against Colletotrichum gloeosporioides that causes anthracnose disease in walnut trees. B. velezensis CE 100 produced a maximum of 62.1 units mL-1 (132.9 units mL-1) chitinase and 5.2 units mL-1 (9.4 units mL-1) β-1,3-glucanase enzymes in the broth culture (crude enzyme fraction), and inhibited spore germination and mycelial growth of C. gloeosporioides by 81.6% and 22.6%, respectively, at 100µlmL-1 of crude enzyme fraction. The inoculation of B. velezensis CE 100 induced the production of pathogenesis-related (PR) chitinase in walnuts by 2.1-fold, and to a lesser extent PR β-1,3-glucanase, and reduced anthracnose disease severity by 3.0-fold compared to the control group. The bacterium produced a maximum of 11.4µgmL-1 indole-3-acetic acid (IAA) and improved the chlorophyll content, shoot length, and root collar diameter of walnut trees compared to the fungicide treatment and control groups. B. velezensis CE 100 demonstrated the prospect of controlling walnut anthracnose by direct antagonism and ISR against C. gloeosporioides, while simultaneously enhancing walnut growth through IAA production.

Induced Systemic Resistance-Mediated Defense Against Alternaria Blight Disease in Lentil by Pesticide Degrading Plant Growth-Promoting Rhizobacteria.

Enzymatic and antioxidative responses are key defense mechanisms in plants following pathogen invasion, collectively known as induced systemic resistance (ISR). Alternaria sp., a well-known soil-borne pathogen, causes blight diseases in various crops. This study investigates the defence response in lentil plants through the treatment-induced application of two multipotent pesticide degrading plant growth-promoting rhizobacteria (PGPR), Bacillus cereus and Bacillus safensis, to mitigate the destructive effects of Alternaria. Both bacterial strains were applied in different carrier-based bioformulations via soil drenching. We assessed the modulation of defense-related enzymes by various combinational treatments with the Alternaria pathogen. The in vitro production of antimicrobial compounds was analyzed using GC-MS to confirm their pathogen-suppressive capabilities. Field trials showed a positive correlation between treatments and improvements in yield and growth index (GI). The highest (180%) enzymatic induction of phenylalanine ammonia lyase (PAL) followed by catalase (CAT)(100%) and polyphenol oxidase (PPO) (54%), was observed in treatments with B. cereus alone or in combination with B. safensis, in presence of Alternaria, in respect to the control. In vitro analysis revealed the production of antimicrobial compounds, including benzoic acid derivatives, cyclotetrasiloxanes, hexacosane, chlorpyrifos, and phthalates, which may contribute to pathogen suppression. Our findings demonstrate that these biocontrol agents (BCAs) not only stimulate the plant's enzymatic defense system but also enhance growth, seed yield and produce several antimicrobial compounds in vitro. Thus, pesticide-tolerant PGPR, used in this study, exhibit both disease control and plant growth-promoting properties, offering promising applications in sustainable agriculture.

The potential of Paraburkholderia species to enhance crop growth.

Agrochemicals are the primary alternative for maintaining the high yields necessary to produce sufficient plant-based foods to supply the world population. In recent decades, one of the most extensively explored alternatives to replace agrochemicals and reduce their environmental impact has been the use of microorganism-based products to boost crop yields with less environmental impact. This review focuses on the results of studies that have demonstrated the potential of the genus Paraburkholderia to increase crop yields and be utilized in biofertilizers and biocontrol products. A literature search was performed electronically considering articles and books published until August 19, 2024. We identified 24 species of Paraburkholderia with the ability to improve crop yields after their inoculation by different methods on seeds, seedlings, plantlets, adult crops, or fruits. The effects of these bacteria have been tested under laboratory, greenhouse, or field conditions. These Paraburkholderia species mediate their positive impact on crop growth by direct and indirect plant growth-promoting mechanisms, which include improving nutrient uptake, stimulating growth by phytohormone production, regulation and stimulation of metabolic pathways, induction of abiotic stress tolerance, and disease control by direct pathogen inhibition or induction of systemic resistance in plants. The literature reviewed here supports the use of Paraburkholderia in bio-inputs under the actual panorama of climate change and the necessity to increase sustainable agriculture worldwide.

Priming of ash saplings with a low virulent Hymenoscyphus fraxineus strain as a possible disease control approach for reducing symptoms of ash dieback

Ash dieback is a tree disease caused by the fungal pathogen Hymenoscyphus fraxineus. Since its introduction into Europe, it has caused widespread and significant losses of the European ash, Fraxinus excelsior. Inoculations of F. excelsior with a low virulent H. fraxineus isolate were assessed as a promising method for reducing symptoms associated with ash dieback, presumably by triggering systemic induced resistance. Two strains of H. fraxineus were chosen based on observations of high and low in planta virulence. Crude extracts obtained from cultures of the highly virulent strain were more phytotoxic in a leaf puncture assay than ones obtained from the low virulent strain. UHPLC-DAD-MS/MS data identified the phytotoxin viridiol and the potential phytotoxin hyfraxin A in both cultures. However, the production of these compounds in vitro did not correspond with virulence in planta. To test the effects of priming, saplings of F. excelsior were first inoculated with the low virulent strain and subsequently with the highly virulent strain. On average, necrosis expansion on the stems was reduced by 53% in primed saplings at the end of the 14-week monitoring period, thus providing proof of the priming concept. These results contribute to our understanding of a possible integrated biological disease control approach for increasing resistance in saplings and reducing potential damages associated with pathogens, particularly during nursery propagation, out-planting and through the establishment phase. We discuss results in the context of relevant literature and summarise the limited availability of literature on priming and underlying principles in trees.

Seed microbiome in crop disease management

Abstract Sustainable agriculture needs innovative approaches because of the increasing demand for food in which the plant microbiome helps in increase crop production and protection which leads to reduce the use of chemical fertilizers. The microbiome comprises a variety of microorganisms that reside in plant parts such as leaves, stems, roots, flowers and seeds. In particular, the seed microbiome, which inhabits the seed surface and internal tissues, offers an opportunity to improve plant health and resilience to biotic and abiotic stresses. They help to tolerate stress and inhibit the pathogens through induced systemic resistance (ISR), production of antimicrobial, volatile compounds and competition for nutrients and space. These beneficial microorganisms within the microbiome are isolated and characterized using culture-dependent and culture-independent methods via modern omics technology called metagenomics. The importance of the seed microbiome in plant defence mechanisms against pathogens and the factors that affect the composition of the microbiome, such as plant genotype, agricultural practices and environmental impact are addressed in detail in this review.

The Crossregulation Triggered by Bacillus Strains Is Strain-Specific and Improves Adaptation to Biotic and Abiotic Stress in Arabidopsis.

Plants are sessile organisms that overcome environmental stress by activating specific metabolic pathways, leading to adaptation and survival. In addition, they recruit beneficial bacterial strains to further improve their performance. As plant-growth-promoting rhizobacteria (PGPR) are able to trigger multiple targets to improve plant fitness, finding effective isolates for this purpose is of paramount importance. This metabolic activation involves the following two stages: the priming pre-challenge with no evident changes, and the post-challenge, which is characterized by a faster and more intense response. Eight Bacillus strains, obtained in a previous study, were tested for their ability to improve plant growth, and to protect Arabidopsis thaliana plants against biotic and abiotic stress. After the 16S rRNA gene sequencing, three isolates were selected for their ability to improve growth (G7), and to protect against biotic and abiotic stress (H47, mild protection, with a similar intensity for biotic and abiotic stress; L44, the highest protection to both); moreover the expression of Non-Expresser of Protein Resistance Gene 1 (NPR1) and Protein resistance (PR1) as markers of the Salicylic Acid (SA) pathway, and lipooxygenase (LOX2) and plant defensin gene (PDF1) as markers of the Ethylene/Jasmonic Acid (Et/Ja) pathway, was determined 24 h after the stress challenge and compared to the expression in non-stressed plants. The results indicated that (i) the three strains prime Arabidopsis according to the more marked and faster increases in gene expression upon stress challenge, (ii) all three strains activate the SA-mediated and the Et/Ja-mediated pathways, therefore conferring a wide protection against stress, and (iii) PR1 and PDF1, traditionally associated to Systemic Acquired Resistance (SAR) and Induced Systemic Resistance (ISR) protection against pathogenic stress, are also overexpressed under abiotic stress conditions. Therefore, it appears that the priming of the plant adaptive metabolism is strain-dependent, although each stress factor determines the intensity in the response of the expression of each gene; hence, the response is determined by the following three factors: the PGPR, the plant, and the stress factor.

Metabolite profiling of PGPR Bacillus subtilis BGKMR1: A potential strategy for managing Fusarium equiseti causing wilt in bitter gourd (Momordica charantia L.)

Wilt caused by Fusarium equiseti is one of the most destructive diseases that leads to substantial yield loss in bitter gourd. The F. equiseti strain CBEFE1((PQ111513.1) which was identified morphologically with falcate shaped three septate macroconidia and oval shaped microconidia and molecularly confirmed through amplification of the ITS region at 560bp was used for this study. Plant growth promoting rhizobacteria (PGPR) act as a sustainable biocontrol agent against major plant pathogens through multiple mode of actions. PGPR were isolated from native rhizopshere region in bitter gourd. The isolated PGPR Bacillus subtilis BGKMR 1 shows maximum mycelial inhibition of 68.73 % against F. equiseti in dual plate assay. The presence of metabolites produced by B. subtilis and F. equiseti along with its interaction were identified through the GCMS profiling. Primarily, pathogenic compound squalene (8.88 %) was identified in F. equiseti and antifungal compound 1,4-benzenedicarboxylic acid (6.1 %) was identified in B. subtilis. Further, B. subtilis BGKMR 1 during its interaction shows propanoic acid (14.69 %) which was found to have effectiveness against F. equiseti. KEGG analysis revealed pyrimidine metabolism in F. equiseti and nitrogen, alanine, aspartate and glutamate metabolism in B. subtilis and propanoate metabolism pathways were detected during its interaction. B. subtilis BGKMR 1 promote the seed germination rate upto 96 % and vigor index to 1919.04 when compared to control. The seed treatment with soil application of B. subtilis BGKMR1 reduced disease incidence upto 25.95 % under glass house condition. Moreover, B. subtilis BGKMR1 treated plants shows enhanced defense enzymes activity such as peroxidase, polyphenol oxidase and phenylalanine ammonia-lyase indicating induction of systemic resistance. Therefore, B. subtilis BGKMR 1 contains novel antifungal metabolites which were identified via GC-MS and induced defense enzyme activity highlights its practical application as a sustainable and eco-friendly solution for managing wilt disease in bitter gourd.

Impact of gibberellic acid GA3, quantum dot biochar, and rhizosphere bacteria on fenugreek plant growth and stress responses under lead stress

Lead (Pb) is a stress that can cause problems with several aspects of a plant’s metabolism, potentially impeding the plant’s ability to grow and develop. The use of gibberellic acid (GA3), quantum dot biochar (QDBC), and rhizobacteria (RB) can be effective methods to overcome this problem. Gibberellic acid is a crucial plant hormone that regulates plant growth, cell division, tissue differentiation, flowering, photosynthesis, and transpiration rate. It also significantly impacts crop resilience to stress, affecting plant morphology, enzymatic activity, and physiology. Biochar, a soil supplement, enhances plant development soil health, and reduces stress effects. Due to its large surface area and porosity, it increases soil water-holding capacity, nutrient retention, and microbial activity. Quantum dots, semiconductor nanoparticles, have been proposed as a potential method to alleviate plant stress by acting as antioxidants, reducing oxidative stress, and controlling nutrient and growth regulators. Rhizobacteria, soil bacteria in plant roots, stimulate plant growth, nutrient absorption, and harvesting capacity. They produce phytohormones, increase mineral and nitrogen accessibility, and can induce systemic resistance (ISR), affecting plant defense. This study investigates the effects of combining GA3, QDBC, and RB as amendments to fenugreek, both with 500 Pb stress and without Pb stress. Treatments (control, 0.25 GA3mg/L-QDBC, 0.5 GA3mg/L-QDBC, 0.25 GA3mg/L-QDBC + RB, and 0.5 GA3mg/L-QDBC + RB) were applied in six replications using a completely randomized design. Results demonstrate that the combination of 0.5 GA3mg/L-QDBC + RB with 500 Pb stress led to significant enhancements in fenugreek shoot fresh weight (15.62%), root fresh weight (73.53%), shoot dry weight (24.00%), and root dry weight (36.53%) compared to the control. Additionally, there were notable improvements in chlorophyll a (57.23%), chlorophyll b (19.21%), and total chlorophyll (36.23%) compared to the control under Pb stress, also showing the potential of 0.5 GA3mg/L-QDBC + RB with 500 Pb stress. The study suggests that combining 0.5 GA3mg/L-QDBC + RB with 500 Pb stress can effectively mitigate Pb stress in fenugreek.

A Review on Genetic Mechanisms of Plant-pathogen Resistance in Crop Breeding

Plant-pathogen resistance is a critical component of sustainable agriculture, essential for protecting crops from devastating diseases and ensuring global food security. This review explores the genetic mechanisms underlying plant-pathogen resistance, focusing on advances in breeding strategies and genetic engineering. Resistance (R) genes, the cornerstone of plant immunity, are categorized by their structural features, including nucleotide-binding site-leucine-rich repeat (NBS-LRR) domains, and function through pathways such as Effector-Triggered Immunity (ETI). The salicylic acid (SA) pathway, crucial for Systemic Acquired Resistance (SAR), and the jasmonic acid (JA) and ethylene (ET) pathways, which drive Induced Systemic Resistance (ISR), are pivotal in orchestrating plant defense responses. Emerging molecular tools like CRISPR-Cas9 enable precise gene editing to enhance R gene function and target susceptibility (S) genes, offering novel pathways to engineer durable resistance. Transgenic approaches, including the introduction of novel R genes and the expression of antimicrobial proteins, have expanded the genetic toolkit for combating pathogens. RNA interference (RNAi) technology further allows for the silencing of critical pathogen genes, adding a layer of defense. Traditional breeding methods, such as hybridization and backcrossing, remain integral, particularly when combined with Marker-Assisted Selection (MAS) and Genomic Selection (GS). MAS facilitates the efficient incorporation of resistance traits using molecular markers, while GS leverages genome-wide data to predict resistance, significantly enhancing breeding efficiency. Challenges such as the rapid evolution of pathogens, resistance breakdown, and climate change-induced shifts in disease dynamics pose significant threats. These challenges necessitate an integrated approach, combining genetic and genomic tools with sustainable disease management practices, such as the use of beneficial microorganisms, precision agriculture, and diversified cropping systems. Future research must focus on understanding the molecular basis of resistance durability, improving predictive models for resistance traits, and developing climate-resilient crop varieties. This integrated strategy is crucial for mitigating disease impact, enhancing crop resilience, and ensuring sustainable agricultural productivity in the face of environmental and biological challenges.

Unveiling Metabolic Crosstalk: Bacillus-Mediated Defense Priming in Pine Needles Against Pathogen Infection.

Background/Objectives: Plant growth-promoting rhizobacteria (PGPR), particularly Bacillus spp., are pivotal in enhancing plant defense mechanisms against pathogens. This study aims to investigate the metabolic reprogramming of pine needles induced by Bacillus csuftcsp75 in response to the pathogen Diplodia pinea P9, evaluating its potential as a sustainable biocontrol agent. Methods: Using liquid chromatography-mass spectrometry (LC-MS/MS), we performed a principal component analysis and a cluster analysis to assess the metabolic alterations in treated versus control groups. This study focused on specific metabolites associated with plant defense. Results: Our findings indicate that treatment with Bacillus csuftcsp75 significantly modifies the metabolic profiles of pine needles, leading to notable increases in metabolites associated with flavonoid biosynthesis, particularly phenylpropanoid metabolism, as well as amino acid metabolism pathways. These metabolic changes indicate enhanced systemic acquired resistance (SAR) and induced systemic resistance (ISR), with treated plants exhibiting elevated levels of defense-related compounds such as 5-hydroxytryptophol and oleanolic acid. Conclusions: This study reveals that Bacillus csuftcsp75 enhances defense against pathogen P9 by modulating pine needle metabolism and activating key immune pathways, inducing systemic acquired resistance and induced systemic resistance, offering a natural alternative to chemical pesticides in sustainable agriculture.

A Review on Plant-microbe Interactions and its Defence Mechanism

Plant-microbe interactions are fundamental to plant health, growth, and defense, influencing agricultural productivity and ecosystem dynamics. These interactions range from symbiotic relationships, such as those with mycorrhizal fungi and nitrogen-fixing bacteria, to pathogenic encounters that trigger complex plant immune responses. Beneficial microbes, including rhizobacteria, mycorrhizae, and endophytes, play a crucial role in enhancing plant defenses through mechanisms like induced systemic resistance (ISR) and production of antimicrobial compounds. Advances in our understanding of these interactions have enabled the development of innovative strategies for crop protection, such as the use of biocontrol agents and microbial inoculants. Additionally, plant breeding and genetic engineering have been employed to introduce resistance genes and modify plant immune responses, resulting in disease-resistant varieties. However, harnessing plant-microbe interactions for sustainable agriculture faces challenges due to the complexity of these interactions in natural environments and the influence of abiotic factors. Limitations in research methodologies, such as difficulties in isolating and studying unculturable microbes, further complicate the translation of findings into practical applications. To overcome these barriers, future research should focus on integrating multi-omics approaches, employing synthetic microbial communities (SynComs), and leveraging CRISPR/Cas technologies for precise manipulation of plant and microbial genes. Microbiome engineering holds promise for promoting beneficial microbial communities, improving plant resilience, and reducing chemical inputs in agriculture. Addressing these challenges will be critical for realizing the full potential of plant-microbe interactions, ultimately contributing to sustainable crop production, improved food security, and ecosystem health. This review highlights current advances, applications, and future directions in the study of plant-microbe interactions, emphasizing their significance for modern agriculture.

Exploring the antifungal activity of clove oil (Syzygium aromaticum) against wilt disease caused by Fusarium equiseti in bitter gourd (Momordica charantia L.)

This study investigates the isolation and characterization of Fusarium equiseti, a fungal pathogen causing wilt in bitter gourd. It explores the antifungal activity of essential oils, particularly clove oil, as a natural management approach. The pathogen was isolated from wilt-infected bitter gourd stems and it was confirmed as F. equiseti morphologically by the presence of three-septate falcate macroconidia and globose microconidia and also confirmed molecularly by PCR amplification of the ITS region (PP501044.1). Among the tested essential oils, clove oil demonstrated the highest mycelial growth inhibition (100%) at a concentration of 0.5%, followed by peppermint, wintergreen and tea tree oils. In comparison, neem oil exhibited the least inhibition (15.54%). GC-MS analysis of clove oil revealed 38 compounds, where eugenol is the predominant compound that played a crucial role in antifungal activity. Additionally, metabolic analysis revealed several enriched pathways in F. equiseti during its interaction with clove oil, particularly those involved in lipid metabolism and energy production. Pot culture experiments confirmed the efficacy of clove oil in reducing disease severity and incidence in bitter gourd, achieving a 66.99 % reduction when combined with soil application.Furthermore, clove oil-treated plants showed increased activity of defense-related enzymes, including peroxidase (PO), polyphenol oxidase (PPO) and phenylalanine ammonia-lyase (PAL), suggesting the induction of systemic resistance. This study highlights the potential of clove oil as an eco-friendly alternative to synthetic fungicides for managing F. exquisite-induced wilt in bitter gourd. Future research should focus on optimizing clove oil application methods and understanding its interactions with fungal pathogens at the molecular level to enhance its efficacy in sustainable disease management.

The biology and chemistry of a mutualism between a soil bacterium and a mycorrhizal fungus

Arbuscular mycorrhizal (AM) fungi (e.g., Rhizophagus species) recruit specific bacterial species in their hyphosphere. However, the chemical interplay and the mutual benefit of this intricate partnership have not been investigated yet, especially as it involves bacteria known as strong producers of antifungal compounds such as Bacillus velezensis. Here, we show that the soil-dwelling B.velezensis migrates along the hyphal network of the AM fungus R.irregularis, forming biofilms and inducing cytoplasmic flow in the AM fungus that contributes to host plant root colonization by the bacterium. During hyphosphere colonization, R.irregularis modulates the biosynthesis of specialized metabolites in B.velezensis to ensure stable coexistence and as a mechanism to ward off mycoparasitic fungi and bacteria. These mutual benefits are extended into a tripartite context via the provision of enhanced protection to the host plant through the induction of systemic resistance.

Research on the mechanism of Bacillus velezensis A-27 in enhancing the resistance of red kidney beans to soybean cyst nematode based on TMT proteomics analysis.

Soybean cyst nematode (SCN) poses a significant challenge to red kidney beans cultivation, resulting in yield losses and quality deterioration. This study investigates the molecular mechanisms using Tandem Mass Tag (TMT) based proteomics technology to explore how the plant growth-promoting rhizobacterium (PGPR) Bacillus velezensis A-27 enhances the resistance of red kidney beans against SCN. The results revealed that out of 1,374 differentially expressed proteins (DEPs) in the red kidney beans roots, 734 DEPs were upregulated and 640 DEPs were downregulated in the A-27 + J2 vs J2 treatment group. KEGG analysis revealed that 14 DEPs were involved in the α-LeA metabolic pathway, crucial for the biosynthesis of jasmonic acid (JA) in plants. Quantitative real-time PCR (qRT-PCR) confirmed the upregulation of 4 key genes (PLA1, AOS, AOC, ACX) in the JA biosynthesis pathway, while enzyme-linked immunosorbent assay (ELISA) demonstrated a significant increase in JA content in the roots. The study demonstrates that B. velezensis A-27 stimulates induced systemic resistance (ISR) in red kidney beans, and induce JA biosynthesis by regulating the expression of key enzymes in the α-LeA metabolic pathway. This enhances the plant's defense against SCN, providing a theoretical foundation for the potential use of B. velezensis A-27 as a biocontrol agent for managing SCN in leguminous crops.

Modulation of Plant Transcription Factors and Priming of Stress Tolerance by Plant Growth-Promoting Bacteria: A Systematic Review.

Plant growth-promoting bacteria (PGPB) have been shown to improve plant growth and stress tolerance through mechanisms including improved access to nutrients and biotic competition with pathogens. As such, the use of PGPB can help to address challenges to crop productivity, however, information on interactions between PGPB and their plant hosts, especially at the level of gene regulation, is distributed across diverse studies involving several different plants and PGPB. For this review, we analysed recent research publications reporting specifically on plant transcription factor (TF) expression in association with PGPB, to determine if there are any common findings and to identify gaps that offer opportunities for focused future research. The inoculation of plants with PGPB elicits a dynamic and temporal response. Initially, there is an upregulation of defence-responsive TFs, followed by their downregulation in an intermediate phase, and finally, another upregulation, providing longer term stress tolerance. PGPB-priming activates plant defences in the form of induced systemic resistance (ISR), often via the MAMP/MAPK pathways and involving one or more of the major plant hormone-signalling pathways and their crosstalk. Following PGPB-priming, the TFs families most commonly reported as expressed across different plants and for different pathogens are ERF and WRKY, while the TFs most commonly expressed across different plants for different abiotic stresses are ERF and DREB. There were inconsistencies between studies regarding the timing of the shift from the initial phase to the intermediate phase, and some of the TFs expressed during this process have not been fully characterized. This calls for more research to investigate the regulatory functions and phases of TF expression, to enhance crop resilience. Most reports on abiotic stresses have focused on salinity and drought, with fewer studies addressing nutrient deficiency, heavy metals, flooding, and other stresses, highlighting the need for further research in these areas.

The decision for or against mycoparasitic attack by Trichoderma spp. is taken already at a distance in a prey-specific manner and benefits plant-beneficial interactions

BackgroundThe application of plant-beneficial microorganisms as bio-fertilizer and biocontrol agents has gained traction in recent years, as both agriculture and forestry are facing the challenges of poor soils and climate change. Trichoderma spp. are gaining popularity in agriculture and forestry due to their multifaceted roles in promoting plant growth through e.g. nutrient translocation, hormone production, induction of plant systemic resistance, but also direct antagonism of other fungi. However, the mycotrophic nature of the genus bears the risk of possible interference with other native plant-beneficial fungi, such as ectomycorrhiza, in the rhizosphere. Such interference could yield unpredictable consequences for the host plants of these ecosystems. So far, it remains unclear, whether Trichoderma is able to differentiate between plant-beneficial and plant-pathogenic fungi during the process of plant colonization.ResultsWe investigated whether Trichoderma spp. can differentiate between beneficial ectomycorrhizal fungi (represented by Laccaria bicolor and Hebeloma cylindrosporum) and pathogenic fungi (represented by Fusarium graminearum and Alternaria alternata) in different confrontation scenarios, including a newly developed olfactometer “race tube”-like system. Using two independent species, T. harzianum and T. atrobrunneum, with plant-growth-promoting and immune-stimulating properties towards Populus x canescens, our study revealed robustly accelerated growth towards phytopathogens, while showing a contrary response to ectomycorrhizal fungi. Transcriptomic analyses identified distinct genetic programs during interaction corresponding to the lifestyles, emphasizing the expression of mycoparasitism-related genes only in the presence of phytopathogens.ConclusionThe findings reveal a critical mode of fungal community interactions belowground and suggest that Trichoderma spp. can distinguish between fungal partners of different lifestyles already at a distance. This sheds light on the entangled interactions of fungi in the rhizosphere and emphasizes the potential benefits of using Trichoderma spp. as a biocontrol agent and bio-fertilizer in tree plantations.

Bacillus licheniformisYB06: A Rhizosphere-Genome-Wide Analysis and Plant Growth-Promoting Analysis of a Plant Growth-Promoting Rhizobacterium Isolated from Codonopsis pilosula.

Codonopsis pilosula, commonly known as Dangshen, is a valuable medicinal plant, but its slow growth and susceptibility to environmental stress pose challenges for its cultivation. In pursuit of sustainable agricultural practices to enhance the yield and quality of Dangshen, the present study isolated a bacterial strain exhibiting plant growth-promoting potential from the rhizosphere of C. pilosula. This strain was subsequently identified as Bacillus licheniformisYB06. Assessment of its plant growth-promoting attributes revealed the potential of B. licheniformis YB06 as a biofertilizer. Whole-genome sequencing of B. licheniformis YB06 revealed a genome size of 4,226,888 bp with a GC content of 46.22%, harboring 4325 predicted protein-coding sequences. Genomic analysis of B. licheniformis YB06 revealed a diverse array of genes linked to induced systemic resistance (ISR) and plant growth-promoting (PGP) traits, encompassing phytohormone production, nitrogen assimilation and reduction, siderophore biosynthesis, phosphate solubilization, biofilm formation, synthesis of PGP-related amino acids, and flagellar motility. Seed germination assays demonstrated the positive effects of B. licheniformis YB06 on the germination and growth of C. pilosula seedlings. Furthermore, we explored various fertilization regimes, particularly the B. licheniformis YB06-based biofertilizer, were investigated for their impact on the structure and diversity of the C. pilosula rhizosphere soil bacterial community. Our findings revealed that fertilization significantly impacted soil bacterial composition and diversity, with the combined application of B. licheniformis YB06-based biofertilizer and organic fertilizer exhibiting a particularly pronounced enhancement of rhizosphere bacterial community structure and diversity. This study represents the first report on the beneficial effects of B. licheniformis YB06 on both the growth of C. pilosula and the composition of its rhizosphere soil microbial community. These findings provide a theoretical foundation and practical guidance for the development of novel bio-organic compound fertilizers, thereby contributing to the sustainable cultivation of C. pilosula.

Rice sheath blight disease control by native endophytic Bacillus subtilis from Kuttanad, a Globally Important Agricultural Heritage System

ABSTRACT Kuttanad in India is known as ‘the rice bowl of Kerala’ and renowned for its unique rice cultivation system that is below sea level. However, rice production in this wetland ecosystem is seriously threatened by sheath blight disease caused by the fungus Rhizoctonia solani, which has resulted in a significant decline in grain quality and a 50% loss in yield. In the present study, we isolated two endophytic Bacillus subtilis strains, NIIST B616 and NIIST B627, from the roots of rice plants growing in the Kuttanad region and tested their efficacy in controlling sheath blight disease. We found that rice plants inoculated with a combination of both Bacillus strains and R. solani had a 64.71% lower disease incidence and a 31.02% higher harvest index than plants treated with R. solani alone. An analysis of defence-related enzymes and chemicals revealed that treatment with both isolates together greatly enhanced levels of l-phenylalanine ammonia-lyase (PAL; 2.8 fold), peroxidase (POX; 7.4 fold), polyphenol oxidase (PPO; 4.5 fold), and total phenol (8.5 fold) compared with plants treated solely with R. solani, indicating that these isolates significantly increased plant defence responses through induced systemic resistance (ISR), and this finding was validated through a split-root experiment. More detailed analysis using gas chromatography–tandem mass spectrometry (GC-MS/MS) and liquid chromatography–tandem mass spectrometry (LC-MS/MS) techniques revealed that cyclo-(Pro-Leu) and cyclo-(Pro-Phe) were the major components responsible for the antifungal properties of the two isolates and their capacity to trigger ISR in plants. Thus, the Bacillus strains and their metabolites may be deemed viable alternatives for controlling the prevalence of sheath blight disease in rice plants and augmenting rice production at unique locations such as Kuttanad.

Pseudomonas thivervalensis K321, a promising and effective biocontrol agent for managing apple Valsa canker triggered by Valsa mali

Plant growth-promoting rhizobacteria (PGPR) have been reported to suppress various diseases as potential bioagents. It can inhibit disease occurrence through various means such as directly killing pathogens and inducing systemic plant resistance. In this study, a bacterium isolated from soil showed significant inhibition of Valsa mali. Morphological observations and phylogenetic analysis identified the strain as Pseudomonas thivervalensis, named K321. Plate confrontation assays demonstrated that K321 treatment severely damaged V. mali growth, with scanning electron microscopy (SEM) observations showing severe distortion of hyphae due to K321 treatment. In vitro twigs inoculation experiments indicated that K321 had good preventive and therapeutic effects against apple Valsa canker (AVC). Applying K321 on apples significantly enhanced the apple inducing systemic resistance (ISR), including induced expression of apple ISR-related genes and increased ISR-related enzyme activity. Additionally, applying K321 on apples can activate apple MAPK by enhancing the phosphorylation of MPK3 and MPK6. In addition, K321 can promote plant growth by solubilizing phosphate, producing siderophores, and producing 3-indole-acetic acid (IAA). Application of 0.2% K321 increased tomato plant height by 53.71%, while 0.1% K321 increased tomato fresh weight by 59.55%. Transcriptome analysis revealed that K321 can inhibit the growth of V. mali by disrupting the integrity of its cell membrane through inhibiting the metabolism of essential membrane components (fatty acids) and disrupting carbohydrate metabolism. In addition, transcriptome analysis also showed that K321 can enhance plant resistance to AVC by inducing ISR-related hormones and MAPK signaling, and application of K321 significantly induced the transcription of plant growth-related genes. In summary, an excellent biocontrol strain has been discovered that can prevent AVC by inducing apple ISR and directly killing V. mali. This study indicated the great potential of P. thivervalensis K321 for use as a biological agent for the control of AVC.

Effect of hyaluronic acid-stabilized silver nanoparticles on lettuce (Lactuca sativa L.) seed germination

Nanotechnology has brought significant advancements to agriculture through the development of engineered nanomaterials (ENPs). Silver nanoparticles (AgNPs) capped with polysaccharides have been applied in agricultural diagnostics, crop pest management, and seed priming. Hyaluronic acid (HA), a natural polysaccharide with bactericidal properties, has been considered a growth regulator for plant tissues and an inducer of systemic resistance against plant diseases. Additionally, HA has been employed as a stabilizing agent for AgNPs. This study investigated the synthesis and effects of hyaluronic acid-stabilized silver nanoparticles (HA-AgNPs) as a seed priming agent on lettuce (Lactuca sativa L.) seed germination. HA-AgNPs were characterized using several techniques, exhibiting spherical morphology and good colloidal stability. Germination assays conducted with 0.1, 0.04, and 0.02 g/L of HA-AgNPs showed a concentration-dependent reduction in seed germination. Conversely, lower concentrations of HA-AgNPs significantly increased germination rates, survival, tolerance indices, and seed water absorption compared to silver ions (Ag+). SEM/EDS indicated more significant potential for HA-AgNPs internalization compared to Ag+. Therefore, these findings are innovative and open new avenues for understanding the impact of Ag+ and HA-AgNPs on seed germination.