Antagonistic Potential Research Articles

Strong antagonism of an endophyte of Fraxinus excelsior towards the ash dieback pathogen, Hymenoscyphus fraxineus, is mediated by the antifungal secondary metabolite PF1140.

Ash dieback, caused by the fungal pathogen Hymenoscyphus fraxineus (Helotiales, Ascomycota), is threatening the existence of the European ash, Fraxineus excelsior. During our search for biological control agents for this devastating disease, endophytic fungi were isolated from healthy plant tissues and co-cultivated with H. fraxineus to assess their antagonistic potential. Among the strains screened, Penicillium cf. manginii DSM 104493 most strongly inhibited the pathogen. Initially, DSM 104493 showed promise in planta as a biocontrol agent. Inoculation of DSM 104493 into axenically cultured ash seedlings greatly decreased the development of disease symptoms in seedlings infected with H. fraxineus. The fungus was thus cultivated on a larger scale in order to obtain sufficient material to identify active metabolites that accounted for the antibiosis observed in dual culture. We isolated PF1140 (1) and identified it as the main active compound in the course of a bioassay-guided isolation strategy. Furthermore, its derivative 2, the mycotoxin citreoviridin (3), three tetramic acids of the vancouverone type (4-6), and penidiamide (7) were isolated by preparative chromatography. The structures were elucidated mainly by NMR spectroscopy and high-resolution mass spectrometry (HRMS), of which compounds 2 and 6 represent novel natural products. Of the compounds tested, not only PF1140 (1) strongly inhibited H. fraxineus in an agar diffusion assay but also showed phytotoxic effects in a leaf puncture assay. Unfortunately, both the latent virulent attributes of DSM 104493 observed subsequent to these experiments in planta and the production of mycotoxins exclude strain Penicillium cf. manginii DSM 104493 from further development as a safe biocontrol agent.IMPORTANCEEnvironmentally friendly measures are urgently needed to control the causative agent of ash dieback, Hymenoscyphus fraxineus. Herein, we show that the endophyte DSM 104493 exhibits protective effects in vitro and in planta. We traced the activity of DSM 104493 to the antifungal natural product PF1140, which unfortunately also showed phytotoxic effects. Our results have important implications for understanding plant-fungal interactions mediated by secondary metabolites, not only in the context of ash dieback but also generally in plant-microbial interactions.

Molecular Characterization Reveals Biodiversity and Biopotential of Rhizobacterial Isolates of Bacillus Spp

Bacillus species appearas the most attractive plant growth-promoting rhizobacteria (PGPR) and alternative to synthetic chemical pesticides. The present study examined the antagonistic potential of spore forming-Bacilli isolated from organic farm soil samples of Allahabad, India. Eighty-seven Bacillus strains were isolated and characterized based on their morphological, plant growth promoting traits and molecular characteristics. The diversity analysis used 16S-rDNA, BOX-element, and enterobacterial repetitive intergenic consensus. Two strains, PR30 and PR32, later identified as Bacillus sp., exhibited potent in vitro antagonistic activity against Ralstonia solanaceorum. These isolates produced copious amounts of multiple PGP traits, such as indole-3-acetic acid (40.0 and 54.5 μg/mL), phosphate solubilization index (PSI) (4.4 and 5.3), ammonia, siderophore (3 and 4 cm), and 1-aminocyclopropane-1-carboxylate deaminase (8.1and 9.2 μM/mg//h) and hydrogen cyanide. These isolates were subjected to the antibiotic sensitivity test. The two potent isolates based on the higher antagonistic and the best plant growth-promoting ability were selected for plant growth-promoting response studies in tomatoe, broccoli, and chickpea. In the pot study, Bacillus subtilis (PR30 and PR31) showed significant improvement in seed germination (27–34%), root length (20–50%), shoot length (20–40%), vigor index (50–75%), carotenoid content (0.543–1.733), and lycopene content (2.333–2.646 mg/100 g) in tomato, broccoli, and chickpea. The present study demonstrated the production of multiple plant growth-promoting traits by the isolates and their potential as effective bioinoculants for plant growth promotion and biocontrol of phytopathogens.

Antagonistic potential and biological control mechanisms of Pseudomonas strains against banded leaf and sheath blight disease of maize

Rhizoctonia solani, the causal agent of banded leaf and sheath blight (BL&SB), poses a significant threat to maize and various crops globally. The increasing concerns surrounding the environmental and health impacts of chemical fungicides have encouraged intensified concern in the development of biological control agents (BCAs) as eco-friendly alternatives. In this study, we explored the potential of 22 rhizobacteria strains (AS1–AS22) isolates, recovered from the grasslands of the Pithoragarh region in the Central Himalayas, as effective BCAs against BL&SB disease. Among these strains, two Pseudomonas isolates, AS19 and AS21, exhibited pronounced inhibition of fungal mycelium growth in vitro, with respective inhibition rates of 57.04% and 54.15% in cell cultures and 66.56% and 65.60% in cell-free culture filtrates. Additionally, both strains demonstrated effective suppression of sclerotium growth. The strains AS19 and AS21 were identified as Pseudomonas sp. by 16S rDNA phylogeny and deposited under accession numbers NAIMCC-B-02303 and NAIMCC-B-02304, respectively. Further investigations revealed the mechanisms of action of AS19 and AS21, demonstrating their ability to induce systemic resistance (ISR) and exhibit broad-spectrum antifungal activity against Alternaria triticina, Bipolaris sorokiniana, Rhizoctonia maydis, and Fusarium oxysporum f. sp. lentis. Pot trials demonstrated significant reductions in BL&SB disease incidence (DI) following foliar applications of AS19 and AS21, with reductions ranging from 25 to 38.33% compared to control treatments. Scanning electron microscopy revealed substantial degradation of fungal mycelium by the strains, accompanied by the production of hydrolytic enzymes. These findings suggest the potential of Pseudomonas strains AS19 and AS21 as promising BCAs against BL&SB and other fungal pathogens. However, further field trials are warranted to validate their efficacy under natural conditions and elucidate the specific bacterial metabolites responsible for inducing systemic resistance. This study contributes to the advancement of sustainable disease management strategies and emphasizes the potential of Pseudomonas strains AS19 and AS21 in combating BL&SB and other fungal diseases affecting agricultural crops.

Secondary Metabolites with Agricultural Antagonistic Potential from Aspergillus sp. ITBBc1, a Coral-Associated Marine Fungus.

A marine-derived fungal strain, Aspergillus sp. ITBBc1, was isolated from coral collected from the South China Sea in Hainan province. Intensive chemical investigation of the fermentation extract of this strain afforded four new secondary metabolites (1-4), named megastigmanones A-C and prenylterphenyllin H, along with four known compounds (5-8). Their structures were elucidated by extensive spectroscopic analysis including one-and two-dimensional (1D and 2D) NMR spectroscopy and high-resolution electrospray ionization mass spectrometry (HR-ESI-MS). The modified Mosher's method was undertaken to determine the absolute configurations of new compounds. The phytotoxic activity test showed that compounds 6-8 exhibited significant antagonistic activity against the germination of Triticum aestivum L. and Oryza sativa L. seeds with a dose-dependent relationship.

Unlocking the growth-promoting and antagonistic power: A comprehensive whole genome study on Bacillus velezensis strains

Bacillus species are extensively documented as plant growth-promoting rhizobacteria, contributing significantly to the enhancement of soil fertility, nutrient recycling, and the control of phytopathogens. Utilizing them as biocontrol agents represents an environmentally friendly strategy, particularly within the rhizospheric community. This study presents the comprehensive genome sequences of three B. velezensis strains (LGMB12, LGMB319, and LGMB426) which were previously isolated from root samples of maize (Zea mays L.), along with a type strain FZB42. The research assesses the capability of the three strains for antagonizing fungi, specifically Fusarium graminearum, Fusarium verticillioides, Colletotrichum graminicola, and Stenocarpella sp. In paired cultures involving maize fungi, treatments containing bacteria B. velezensis exhibited statistically significant differences compared to both negative and positive treatments in terms of antagonism. Furthermore, genome mining techniques were employed to explore their inherent antagonistic potential. The assembly revealed that strains LGMB12, LGMB319, LGMB426, and FZB42 exhibit genome sizes of 4,187,541 bp, 4,244,954 bp, 3,976,537 bp, and 3,990,518 respectively. Their respective G + C content stands at 46.42 %, 46.50 %, 46.51 %, and 46.38 %. Moreover, the genomes present multiple gene clusters responsible for the synthesis of secondary metabolites and carbohydrate-active enzymes (CAZymes). These clusters highlight a diverse array of antibacterial and antifungal properties, complemented by numerous plant growth-promoting genes. These results highlight the potential of B. velezensis LGMB12, LGMB319, and LGMB426 strains as biocontrol and plant growth promotion agents, being promising candidates for further studies in agricultural production, including field trials.

Molecular and aflatoxigenicity analyses of Aspergillus flavus isolates indigenous to grain corn in Malaysia; potentials for biological control.

The present work aimed to distinguish the indigenous Aspergillus flavus isolates obtained from the first (pioneer) grain corn farms in Terengganu, Malaysia, into aflatoxigenic and non-aflatoxigenic by molecular and aflatoxigenicity analyses, and determine the antagonistic capability of the non-aflatoxigenic isolates against aflatoxigenic counterparts and their aflatoxin production in vitro. Seven A. flavus isolates previously obtained from the farms were characterized molecularly and chemically. All isolates were examined for the presence of seven aflatoxin biosynthesis genes, and their aflatoxigenicity were confirmed using high performance liquid chromatography with fluorescence detector (HPLC-FLD). Phylogenetic relationships of all isolates were tested using ITS and β-tubulin genes. Of the seven isolates, two were non-aflatoxigenic, while the remaining were aflatoxigenic based on the presence of all aflatoxin biosynthesis genes tested, and the productions of aflatoxins B1 and B2. All isolates were also confirmed as A. flavus following phylogenetic analysis. The indigenous non-aflatoxigenic isolates were further examined for their antagonistic potential against aflatoxigenic isolates on 3% grain corn agar (GCA). Both non-aflatoxigenic isolates significantly reduced AFB1 production of the aflatoxigenic isolates. The indigenous non-aflatoxigenic A. flavus strains identified in the present work were effective in controlling the aflatoxin production by the aflatoxigenic A. flavus isolates in vitro and can be utilized for in situ testing.

Antagonistic potential of Trichoderma strains isolated from Musa paradisiaca cv. Malnad Rasbale grown farmyards against Foc race 4 pathogen

Foc race 4 is a causative pathogen for Panama wilt disease of Musa Paradisiaca cv. Malnad Rasbale. The cost-effective measure to control rather than the usage of agrochemicals is still not available for this cultivar. Trichoderma strains act as an antagonistic agent against different phytopathogenic fungi including many pathogenic races of Panama wilt-causing pathogens. An attempt has been made to recognize the mode of action of this antagonistic agent in in vitro conditions and interaction between six Trichoderma strains. Foc race 4 was first investigated by dual plate culture method on PDA medium. This study revealed the potential of native strain KUVKU-TH02 for the biological control of Foc race 4 pathogen affecting Malnad Rasbale cultivar in in vivo conditions rather than native isolates KUVKU-TH01, KUVKU-TV01 and KUVKU-TV02. Observations revealed the lysis of hyphal ending in inhibited colonies of the fungal pathogen. Pure culture of isolated fungal strains incubated on potato dextrose broth made a path to isolate DNA for identification and molecular characterization studies. Upon DNA sequencing, native isolates sequences were deposited to NCBI genebank to gain accession IDs. The phylogenetic tree built showed the evolutionary relationship between the isolates and also the potency of native biocontrol isolates against procured isolates.

Bacteriostatic Activity of Janthinobacterium lividum and Purified Violacein Fraction against Clavibacter michiganensis

Clavibacter michiganensis causes plant diseases and is included in the list of microorganisms subject to export control. Janthinobacterium lividum is capable of synthesizing a pigment with antagonistic potential. The purpose of the study was to evaluate the activity of J. lividum VKM B-3705D and the pigment fraction against C. michiganensis VKM Ac-1402. The results of spectrophotometric and nuclear magnetic resonance analysis showed that the pigment synthesized by the J. lividum VKM B-3705D corresponds to violacein. The J. lividum strain demonstrated potential bacteriostatic activity against C. michiganensis VKM Ac-1402 when both strains were co-cultured. Compared to the control (DMSO), the violacein solution suppressed the specific growth of Clavibacter by 57.7%. The mechanism of suppression of the growth of Clavibacter is discussed. One of the ways to suppress the growth of C. michiganensis may be the inhibition of key enzymes. Violacein inhibited the activity of adenosine triphosphatase (ATPase, EC 3.6.1.3) compared to the control (DMSO) by 23.2%. Thus, the current study of the bacteriostatic effect may be a decisive step towards the development of a plant protection product.

Unlocking the Potential of Plant Growth-Promoting Rhizobacteria to Enhance Drought Tolerance in Egyptian Wheat (Triticum aestivum)

Plant growth-promoting rhizobacteria (PGPRs) represent a promising strategy for enhancing plant resilience and yields under drought-stress conditions. This study isolated and characterized PGPR from wheat rhizosphere soil in Egypt. Four PGPR strains were evaluated for an array of plant growth-promoting traits, including IAA production, biofilm formation, siderophore production, nitrogen fixation, ACC deaminase activity, phosphate solubilization, and antagonistic potential. Molecular identification via 16S rRNA sequencing classified three isolates (MMH101, MMH102, and MMH103) within the Bacillus genus and one isolate (MMH104) as Myroides sp. Greenhouse experiments examined the effects of PGPR inoculation on the drought-stressed Egyptian wheat cultivar, Gimmeza-9. Wheat plants inoculated with PGPR isolates showed dramatic improvements in growth parameters and stress tolerance indicators compared to non-inoculated controls when subjected to a 10-day drought period, with Bacillus rugosus (MMH101) inoculation resulting in increases of 61.8% in fresh biomass, 77.2% in dry biomass, 108.5% shoot length, and 134.9% root length. PGPR treatments also elevated the chlorophyll and proline content while reducing malondialdehyde levels. The findings demonstrate the effectiveness of PGPR inoculation in enhancing the morphology, physiology, and drought stress resilience of wheat. Isolated PGPR strains hold promise as biofertilizers for improving cereal productivity under water-deficit conditions.

Red and far-red light improve the antagonistic ability of Trichoderma guizhouense against phytopathogenic fungi by promoting phytochrome-dependent aerial hyphal growth.

Light as a source of information regulates morphological and physiological processes of fungi, including development, primary and secondary metabolism, or the circadian rhythm. Light signaling in fungi depends on photoreceptors and downstream components that amplify the signal to govern the expression of an array of genes. Here, we investigated the effects of red and far-red light in the mycoparasite Trichoderma guizhouense on its mycoparasitic potential. We show that the invasion strategy of T. guizhouense depends on the attacked species and that red and far-red light increased aerial hyphal growth and led to faster overgrowth or invasion of the colonies. Molecular experiments and transcriptome analyses revealed that red and far-red light are sensed by phytochrome FPH1 and further transmitted by the downstream MAPK HOG pathway and the bZIP transcription factor ATF1. Overexpression of the red- and far-red light-induced fluffy gene fluG in the dark resulted in abundant aerial hyphae formation and thereby improvement of its antagonistic ability against phytopathogenic fungi. Hence, light-induced fluG expression is important for the mycoparasitic interaction. The increased aggressiveness of fluG-overexpressing strains was phenocopied by four random mutants obtained after UV mutagenesis. Therefore, aerial hyphae formation appears to be a trait for the antagonistic potential of T. guizhouense.

Characterization and Field Evaluation of Potential Fluorescent Pseudomonas Isolates on Growth and Yield Attributing Characters in Chickpea

The present investigation was conducted at the research and instructional farm, College of Agriculture, Indira Gandhi Krishi Vishwavidyalaya, Raipur, Chhattisgarh, India during rabi (October–December 2019) to evaluate the influence of fluorescent Pseudomonas isolates on chickpeas through characterization and field evaluation. Eighty-eight rhizosphere soil samples were derived from different locations in Bastar and Bilaspur districts of Chhattisgarh, India. Potential isolates were required for fundamental research and practical application of plant growth-promoting rhizobacterial strains on different crops. Among eighty-eight isolates, ten fluorescent Pseudomonas (visible under UV light at 360 nm) emitting strong fluorescence were selected for the course of the investigation and characterized for the production of siderophores, phosphate solubilization, indole acetic acid, 1-aminocyclopropane-1-carboxylic acid deaminase, and analysis of antagonistic potential. Of the 10 Pseudomonas isolates, 9704 was identified as the highest phosphate solubilizer, BSP-23 was identified as the highest indole acetic acid producer, and BSP-19 was the highest siderophore producer. Fluorescent Pseudomonas isolates BS-1, BS-4, 9809, BSP-14, and BSP-19 were identified to possess 1-aminocyclopropane-1-carboxylic acid deaminase-producing ability following qualitative analysis. Our present investigation indicates that beneficial effects of fluorescent Pseudomonas could be achieved through simple and cost-effective seed treatment. Three fluorescent Pseudomonas strains, 9704, BS-14, and 9829, consistently increased seed germination and improved plant growth and yield (BS-37.9% and 9704-35.7%) attributes in chickpeas. Besides, confrontation assays performed against R. bataticola expressed varying levels of inhibition. The phylogenetic affinities of 16S rRNA gene sequencing resolved the species identities of selected isolates.

Green synthesis of metal nanoparticles and study their anti-pathogenic properties against pathogens effect on plants and animals

According to an estimate, 30% to 40%, of global fruit are wasted, leading to post harvest losses and contributing to economic losses ranging from $10 to $100 billion worldwide. Among, all fruits the discarded portion of oranges is around 20%. A novel and value addition approach to utilize the orange peels is in nanoscience. In the present study, a synthesis approach was conducted to prepare the metallic nanoparticles (copper and silver); by utilizing food waste (Citrus plant peels) as bioactive reductants. In addition, the Citrus sinensis extracts showed the reducing activity against metallic salts copper chloride and silver nitrate to form Cu-NPs (copper nanoparticles) and Ag-NPs (Silver nanoparticles). The in vitro potential of both types of prepared nanoparticles was examined against plant pathogenic bacteria Erwinia carotovora (Pectobacterium carotovorum) and pathogens effect on human health Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Moreover, the in vivo antagonistic potential of both types of prepared nanoparticles was examined by their interaction with against plant (potato slices). Furthermore, additional antipathogenic (antiviral and antifungal) properties were also examined. The statistical analysis was done to explain the level of significance and antipathogenic effectiveness among synthesized Ag-NPs and Cu-NPs. The surface morphology, elemental description and size of particles were analyzed by scanning electron microscopy, transmission electron microscopy, energy-dispersive spectroscopy and zeta sizer (in addition polydispersity index and zeta potential). The justification for the preparation of particles was done by UV–Vis Spectroscopy (excitation peaks at 339 nm for copper and 415 nm for silver) and crystalline nature was observed by X-ray diffraction. Hence, the prepared particles are quite effective against soft rot pathogens in plants and can also be used effectively in some other multifunctional applications such as bioactive sport wear, surgical gowns, bioactive bandages and wrist or knee compression bandages, etc.

Biocontrol of tomato pathogens by Bacillus subtilis F62 and its synergistic action in plant growth promotion with Rhizobium sp. L5

ABSTRACT Plant growth-promoting rhizobacteria (PGPR) are recognised for inhibiting pathogens and increasing plant biomass and yield. This study aims to evaluate the antagonistic potential of Bacillus subtilis F62 against fungal diseases of tomatoes and investigates its capability for promoting the growth of tomato seedlings using single-strain inoculation and co-inoculation with Rhizobium sp. L5. The in vitro antagonism of B. subtilis F62 against Alternaria sp., Botrytis sp., Fusarium sp., and Stemphylium sp. was assessed through dual-culture and volatile compounds assays. Furthermore, the antagonism against Botrytis sp. was also evaluated in harvested tomatoes. The growth promotion experiment involved treating tomato seeds with bacterial suspensions through soil drenching and seed soaking. Our results demonstrated the inhibitory ability of B. subtilis F62 against all fungal species, reducing the mycelial growth speed index from 54.7% to 76.6% in the dual-culture assay, and from 14.1% to 70.6% through antagonism via volatile compounds. This bacterium also decreased the incidence and severity of Botrytis sp. by 21% and 18.8%, respectively, in harvested tomatoes. Additionally, the growth promotion assay revealed that co-inoculation of B. subtilis F62 and Rhizobium sp. L5 increased leaf area and root dry weight compared to single-strain inoculation. Therefore, B. subtilis F62 is a promising bacterium for the biocontrol of tomato diseases and an effective plant growth-promoting rhizobacterium, demonstrating its synergistic effect when co-inoculated with Rhizobium sp. L5 on tomato seeds.

Characterisation and toxins analysis of symbiotic bacteria Photorhabdus luminescens isolated from Heterorhabditis indica ICRI-18 strain

Entomopathogenic nematodes are proven alternatives to pesticides in crop protection as they belong to the Heterorhabditidae and Steinernematidae families. The role of entomopathogenic nematodes has expanded considerably in the recent past for their efficacy as biopesticide which is influenced by nematode species and strain. Members of the genus Heterorhabditis have been found to harbor a symbiotic bacteria Photorhabdus sp. When the nematode is ingested by the insect, Photorhabdus sp. is released into the host haemocoel where they multiply rapidly and kill the insect. The main objective of our research was to examine the insect killing toxin property of symbiotic bacteria isolated from the entomopathogenic nematodes Heterorhabditis indica. The antagonistic potential of insecticidal toxin from Photorhabdus sp. was investigated. The results prove that toxic components produced by these bacteria could kill pests either through ingestion or injection. The broad-spectrum antimicrobial property produced by Photorhabdus sp. was analysed by conducting both antibiogram and antibiosis studies.

A comparative study on the synergistic activities of fractions and crude essential oil of Syzygium aromaticum

BackgroundSyzygium aromaticum has been used for over a century because it has biological qualities for several health-related problems, and the crude essential oils are known to contain several components that could be responsible for synergistic or antagonistic potentials in relation to their biological uses. The study was designed to compare the biological activities of the crude essential oil from the bud of Syzygium aromaticum and fractions obtained from column chromatography.Materials and methodsThe essential oil was extracted by hydrodistillation, and two prominent fractions, C1 and C2, were obtained from the column chromatography separation of the crude essential oil. The quantitative phytochemical analysis was done by standard methods, the antioxidant activity was determined by 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid (ABTS) scavenging assays. The antifungal activities were assessed by the agar diffusion method, while the anti-inflammatory activity was done using a lipoxygenase inhibitory assay. The major component observed in the crude and fractions was determined by gas chromatography–mass spectrometry (GC–MS) analysis.ResultsThe phytochemical analysis showed that phenolic acid, tannin, saponin, flavonoids, alkaloids, cardiac glycosides, and terpenoids were present in variable quantities in all of the fractions and crude essential oil. The half-maximal inhibitory concentration (IC50) value for DPPH scavenging activity ranged from 226.1 to 301.2 µg/mL while that of ABTS scavenging activity ranged from 211.0 to 316.0 µg/mL. The lowest value of IC50 for both DPPH and ABTS was observed in fraction C1. The crude essential oil with a minimum inhibitory concentrations (MIC) value of 8.00 mg/mL was the most efficient against Candida albicans, Aspergillus penicillum, and Aspergillus niger. The anti-inflammatory assay showed C1 to have the lowest value of IC50 for the lipoxygenase assay. The major component observed in the crude essential oil as well as fraction C1 was eugenol, while fraction C2 had β-caryophyllene as the major component.ConclusionsThe result showed that all fractions as well as the crude essential oil exhibited antioxidant, antifungal, and anti-inflammatory activities, and the crude essential oil was synergic only with respect to its antifungal activity, while fraction C1 was more efficient as an anti-inflammatory and antioxidant agent.

The antagonistic potential of Trichoderma harzianum against barley leaf-stripe disease

The antagonistic potential of Trichoderma harzianum against barley leaf-stripe disease

Unveiling the Biocontrol Potential of Rhizoplane Bacillus Species against Sugarcane Fusarium Wilt through Biochemical and Molecular Analysis.

Biocontrol is regarded as a viable alternate technique for managing sugarcane wilt disease caused by Fusarium sacchari. Many fungal antagonists against F. sacchari, have been reported, but the potential of bacterial antagonists was explored to a limited extent, so the present study evaluated the antagonistic potential of rhizoplane Bacillus species and their mode of action. A total of twenty Bacillus isolates from the rhizoplane of commercially grown sugarcane varieties were isolated. The potential isolate SRB2 had shown inhibition of 52.30, 33.33, & 44.44% and SRB20 of 35.00, 33.15, & 36.85% in direct, indirect, and remote confrontation respectively against F. sacchari. The effective strains were identified as Bacillus inaquosorum strain SRB2 and B. vallismortis strain SRB20, by PCR amplification of 16S-23S intergenic region. The biochemical studies on various direct and indirect biocontrol mechanisms revealed the production of IAA, Protease, Cellulase, Siderophores, and P solubilization. The molecular analysis revealed the presence of antimicrobial peptides biosynthetic genes like fenD (Fengycin), bmyB (Bacyllomicin) ituC (Iturin) and spaS (Subtilin) which provided a competitive edge to these isolates compared to other Bacillus strains. Under greenhouse experiments, the sett bacterization with SRB2, significantly (P < 0.001) reduced the seedling mortality by > 70% followed by SRB20 in F. sacchari inoculated pots. The study revealed that the isolates B. inaquosorum SRB2 and B. vallismortis SRB20 can be used as potential bioagents against sugarcane Fusarium wilt.

Antagonistic potential of soil fungi as biocontrol agent against rice pathogens

Antagonistic potential of six soil fungi viz., Aspergillus flavus Link., A. fumigatus Fresen., A. niger Tiegh., Penicillium sp., Trichoderma harzianum Refat. and T. viride Pers. against eight pathogenic fungi viz., Alternaria alternata (Fr.) Keissler, Curvularia lunata (Wakker) Boedijn, Drechslera oryzae Breda de Haan (Subramanian and Jain), Fusarium moniliforme Sheldon, F. solani (Mart.) Sacc. Microdochium oryzae (Hashloka and Yokogi) Sam. and Hal., Pestalotiopsis guepinii (Desm.) Stay. and Sarocladium oryzae (Sawada) W. Gams and D. Hawks of rice were evaluated. In colony interaction, the highest growth inhibition (88%) was observed owing to T. harzianum against Alternaria alternata.Volatile substances from soil fungi inhibited the radial growth of the test pathogens which varied from 8.33 to 57.36%.The highest inhibition (57.36%) was found owing to T. harzianum against P. guepinii. The inhibition of mycelial growth of the test pathogens ranged from 29.05 to 64.5% owing to non volatile substances of the soil fungi. The highest mycelial growth inhibition was observed owing to T. harzianum against C. lunata. Trichoderma harzianum may be exploited commercially to control rice pathogens. Bangladesh J. Bot. 53(1): 101-108, 2024 (March)

Antibacterial Properties of Bacterial Endophytes Isolated from the Medicinal Plant Origanum heracleoticum L.

Bacterial endophytic communities associated with medicinal plants synthesize a plethora of bioactive compounds with biological activities. Their easy isolation and growth procedures make bacterial endophytes an untapped source of novel drugs, which might help to face the problem of antimicrobial resistance. This study investigates the antagonistic potential of endophytic bacteria isolated from different compartments of the medicinal plant O. heracleoticum against human opportunistic pathogens. A panel of endophytes was employed in cross-streaking tests against multidrug-resistant human pathogens, followed by high-resolution chemical profiling using headspace-gas chromatography/mass spectrometry. Endophytic bacteria exhibited the ability to antagonize the growth of opportunistic pathogens belonging to the Burkholderia cepacia complex (Bcc). The different inhibition patterns observed were related to their taxonomic attribution at the genus level; most active strains belong to the Gram-positive genera Bacillus, Arthrobacter, and Pseudarthrobacter. Bcc strains of clinical origin were more sensitive than environmental strains. Cross-streaking tests against other 36 human multidrug-resistant pathogens revealed the highest antimicrobial activity towards the Coagulase-negative staphylococci and Klebsiella pneumoniae strains. Interestingly, strains of human origin were the most inhibited, in both groups. Concerning the production of volatile organic compounds (VOCs), the strain Arthrobacter sp. OHL24 was the best producer of such compounds, while two Priestia strains were good ketones producers and so could be considered for further biotechnological applications. Overall, this study highlights the diverse antagonistic activities of O. heracleoticum-associated endophytes against both Bcc and multidrug-resistant (MDR) human pathogens. These findings hold important implications for investigating bacterial endophytes of medicinal plants as new sources of antimicrobial compounds.

DETERMINATION OF ANTIBIOSIS OF Trichoderma species AGAINST FUNGI ASSOCIATED WITH CORN (Zea Mays L.) SPOILAGE

Biological control of food spoilage microorganisms is gaining more attention because it is a safe and cheap technique. This study evaluated the antagonistic potential of Trichoderma species against corn spoilage fungi by plate co-culture technique for seven days. Fungal isolates from corn spoilage were examined morphologically and microscopically. The percentage growth inhibition (PGI) of Trichoderma species against the corn spoilage fungi were A. flavus (15%), A. niger (14%), A. terreus (62.9%), Fusarium spp. (5.9%), Nigrospora spp. (61.4%) and Penicillium spp. (62.5%). The result obtained in this study revealed that Trichoderma spp. had significant inhibitory effects against the growth of fungal pathogens associated with corn spoilage. Therefore, it could be explored for control of post-harvest fungal spoilage of corn. It is recommended that in order to compare the antagonistic strength of the Trichoderma species, different species of Trichoderma should be tested against the same spoilage fungi.