Molecular insights into development of Trichoderma interfusants for multistress tolerance enhancing antagonism against Sclerotium rolfsii Sacc

Trichoderma afroharzianum TRI07 metabolites inhibit Alternaria alternata growth and induce tomato defense-related enzymes

Identifying a viable substitute for the limited array of current antifungal agents stands as a crucial objective in modern agriculture. Consequently, extensive worldwide research has been undertaken to unveil eco-friendly and effective agents capable of controlling pathogens resistant to the presently employed fungicides. This study explores the efficacy of Trichoderma isolates in combating tomato leaf spot disease, primarily caused by Alternaria alternata. The identified pathogen, A. alternata Alt3, was isolated and confirmed through the ITS region (OQ888806). Six Trichoderma isolates were assessed for their ability to inhibit Alt3 hyphal growth using dual culture, ethyl acetate extract, and volatile organic compounds (VOCs) techniques. The most promising biocontrol isolate was identified as T. afroharzianum isolate TRI07 based on three markers: ITS region (OQ820171), translation elongation factor alpha 1 gene (OR125580), and RNA polymerase II subunit gene (OR125581). The ethyl acetate extract of TRI07 isolate was subjected to GC-MS analysis, revealing spathulenol, triacetin, and aspartame as the main compounds, with percentages of 28.90, 14.03, and 12.97%, respectively. Analysis of TRI07-VOCs by solid-phase microextraction technique indicated that the most abundant compounds included ethanol, hydroperoxide, 1-methylhexyl, and 1-octen-3-one. When TRI07 interacted with Alt3, 34 compounds were identified, with major components including 1-octen-3-one, ethanol, and hexanedioic acid, bis(2-ethylhexyl) ester. In greenhouse experiment, the treatment of TRI07 48 h before inoculation with A. alternata (A3 treatment) resulted in a reduction in disease severity (16.66%) and incidence (44.44%). Furthermore, A3 treatment led to improved tomato growth performance parameters and increased chlorophyll content. After 21 days post-inoculation, A3 treatment was associated with increased production of antioxidant enzymes (CAT, POD, SOD, and PPO), while infected tomato plants exhibited elevated levels of oxidative stress markers MDA and H2O2. HPLC analysis of tomato leaf extracts from A3 treatment revealed higher levels of phenolic acids such as gallic, chlorogenic, caffeic, syringic, and coumaric acids, as well as flavonoid compounds including catechin, rutin, and vanillin. The novelty lies in bridging the gap between strain-specific attributes and practical application, enhancing the understanding of TRI07's potential for integrated pest management. This study concludes that TRI07 isolate presents potential natural compounds with biological activity, effectively controlling tomato leaf spot disease and promoting tomato plant growth. The findings have practical implications for agriculture, suggesting a sustainable biocontrol strategy that can enhance crop resilience and contribute to integrated pest management practices.

Salicylic acid-functionalised chitosan nanoparticles restore impaired sucrose metabolism in the developing anther of cotton (Gossypium hirsutum) under heat stress

Nanotechnology provides tremendous potential in agriculture, mitigating climate change impact and improving abiotic stress management strategy. Chitosan nanoparticles (NCS) were synthesised using the ion gelation method and characterised for size (75.5nm in particle size analyser), shape (spherical under scanning electron microscopy) and stability (132.2mV zeta potential). Further, salicylic acid was incorporated into NCS to craft salicylic acid-functionalised chitosan nanoparticles (SA-NCS) and illustrated for size (517nm), shape (spherical) and stability (197.1mV). The influence of the exogenous application of SA-NCS (0.08%) was studied at the reproductive stage of three genotypes of cotton (Gossypium hirsutum ): (1) heat-tolerant Solar-651 BGII; (2) moderately heat-tolerant Solar-701 BGII; and (3) heat-susceptible Solar-805 BGII, exposed to different temperature regimes: (1) H1 (optimal), 32/20±2°C; (2) H2 (sub-optimal), 38/24±2°C; H3 (supra-optimal), 45/30±2°C. Heat stress significantly reduces carbon-fixing Rubisco, enzymes related to sucrose metabolism and pollen tube length. Considering three genotypes and reproductive stages (sepal and anther tissues), activities of Rubisco (sepals), invertase (sepals), sucrose phosphate synthase (anthers), sucrose content (sepals) and pollen tube length were elevated under high-temperature regimes, signifying better source to sink transposition of sucrose influenced by SA-NCS. The study provides new insights into SA-NCS to improve source-sink imbalance and restore sucrose metabolism for better growth of reproductive structure under heat stress in cotton.

Intracellular metabolomics and microRNAomics unveil new insight into the regulatory network for potential biocontrol mechanism of stress-tolerant Tricho-fusants interacting with phytopathogen Sclerotium rolfsii Sacc

The present study employed microRNA (miRNA) sequencing and metabolome profiling of Trichoderma parental strains and fusants during normal growth and interaction with the phytopathogen Sclerotium rolfsii Sacc. In-vitro antagonism indicated that abiotic stress-tolerant Tricho-fusant FU21 was examined as a potent biocontroller with mycoparasitic action after 10 days. During interaction with the test pathogen, the most abundant uprising intracellular metabolite was recognized as l-proline, which corresponds to held-down l-alanine, associated with arginine and proline metabolism, biosynthesis of secondary metabolites, and nitrogen metabolism linked to predicted genes controlled by miRNAs viz., cel-miR-8210-3p, hsa-miR-3613-5p, and mml-miR-7174-3p. The miRNAs- mml-miR-320c and mmu-miR-6980-5p were found to be associated with phenylpropanoid biosynthesis, transcription factors, and signal transduction pathways, respectively, and were ascertained downregulated in potent FU21_IB compared with FU21_CB. The amino benzoate degradation and T cell receptor signaling pathways were regulated by miRNAs cel-miR-8210 and tca-miR-3824 as stress tolerance mechanisms of FU21. The intracellular metabolites l-proline, maleic acid, d-fructose, Myo-inositol, arabinitol, d-xylose, mannitol, and butane were significantly elevated as potential biocontrol and stress-tolerant constituents associated with miRNA regulatory pathways in potent FU21_IB. A network analysis between regulatory miRNA-predicted genes and intracellular metabolomics acknowledged possible biocontrol pathways/mechanisms in potent FU21_IB to restrain phytopathogen.

Biochemical and molecular depictions to develop ech42 gene-specific SCAR markers for recognition of chitinolytic Trichoderma inhibiting Macrophomina phaseolina (Maubl.) Ashby

Trichoderma isolates were inhibited variably in-vitro growth of soil-borne phytopathogen Macrophomina phaseolina (Maubl.) Ashby causes root rot in cotton. The growth inhibition of test-pathogen was found to be higher (90.36%) in T. viride NBAIITv23 followed by T. koningii MTCC796 (85.77%) under dual culture antagonism. The microscopic examination suggested that the antagonists Tv23 and MTCC796 adopted mycoparasitism as a strong mode of action to restrain pathogen growth. However, antagonists T. harzianum NBAIITh1 (77.89%) and T. virens NBAIITvs12 (61.74%) demonstrated strong antibiosis action for growth inhibition of the test pathogen. A significant positive correlation was established between the growth inhibition of M. phaseolina and the release of cell wall degrading enzymes- chitinase (p = 0.001), β-1,3, glucanase (p = 0.01), and protease (p = 0.05) under the influence of pathogen cell wall. The chitinase and β-1,3, glucanase activities were elevated 2.09 and 1.75 folds, respectively, in potent mycoparasitic Tv23 strain influenced by a pathogen cell wall compared to glucose as a carbon source. The three unique DNA-RAPD fragments OPA-07₍₁₀₃₃₎, OPA-16₍₉₈₃₎, and OPO-15_(239), amplified by potent mycoparasitic Tv23 strain, were subjected to DNA sequencing and derived functional 864 bp from OPA-16₍₉₈₃₎ and have sequence homology to ech42 gene with partial CDs of 262 amino acids (nucleotide accession No. KF723016.1 and protein accession No.AHF57046.1). Novel SCAR markers were developed from a functional sequence of OPA-16 fragments and validated across the genomic DNA of eleven Trichoderma antagonists. The novel SCAR markers evolved from the RAPD-SCAR interface to authenticate chitinolytic Trichoderma associated with mycoparasitic action for eco-friendly biocontrol activity.

Exploring conserved and novel MicroRNA-like small RNAs from stress tolerant Trichoderma fusants and parental strains during interaction with fungal phytopathogen Sclerotium rolfsii Sacc

The study investigated potential microRNA-like small RNAs (milRNAs) from multi-stress-tolerant Tricho-fusants and parental strains (P1- Trichoderma virens NBAIITvs12 and P2- Trichoderma koningii MTCC796) for antagonistic activity during interaction with phytopathogen Sclerotium rolfsii. The Trichoderma was cultured in-vitro, with and without antagonism, against the pathogen and total RNA was extracted followed by small RNA library construction and sequencing. The milRNAs were identified by mapping high-quality unique reads against a reference genome. The milRNAs were recognized higher in antagonist Trichoderma during interaction with test pathogen compared to normal growth. The novel milRNAs candidates were found to vary during interaction with the pathogen and normal growth. The gene ontology and functional analysis illustrated that a total of 5828 potential targeted genes were recognized for 93 milRNAs of potent Fu21_IB and 3053 genes for 62 milRNAs of least fusant Fu28_IL. Functional annotation of milRNA-predicted genes integrating KEGG pathways indicates new insights into regulatory mechanisms, by interfering with milRNAs, associated with signal transduction, amino sugar metabolism, benzoate degradation, amino acid metabolism, and steroid and alkaloid metabolism for potential biocontrol of stress-tolerant Tricho-fusant FU21 during interaction with S. rolfsii. The present investigation is the first report of conserved and novel milRNAs from Tricho-fusants and parental strains interacting with S. rolfsii.

Characterization and bioefficacy of green nanosilver particles derived from fungicide-tolerant Tricho-fusant for efficient biocontrol of stem rot (Sclerotium rolfsii Sacc.) in groundnut (Arachis hypogaea L.)

An efficient and eco-friendly bioefficacy of potent Tricho-fusant (Fu21) and its green nanosilver formulation against stem rot (Sclerotium rolfsii) in groundnut was established. Fu21 demonstrated higher in-vitro growth inhibition of pathogen with better fungicide tolerance than the parental strains. The green nanosilver particles were synthesized from the extracellular metabolites of Fu21 and characterized for shape (spherical, 59.34 nm in scanning electron microscope), purity (3.00 KeV, energy dispersive X-ray analysis), size (54.3 nm in particle size analyzer), and stability (53.7 mv, zeta). The field efficacy study exhibited that the seedling emergence was high in seeds treated with green nanosilver (minimum inhibitory concentration-[MIC] 20 µg Ag/ml), and a low disease severity index of stem rot during the crop growth was followed by the live antagonist (Fu21) in addition to seed treatment with a fungicide mix under pathogen infestation. The seed quality analysis of harvested pods revealed a high oil content with balanced fatty acid composition (3.10 oleic/linoleic acid ratio) in green nanosilver treatment under pathogen infestation. The residual analysis suggested that green nanosilver applied at the MIC level as seed treatment yielded similar effects as the control for silver residue in the harvested groundnut seeds. The green nanosilver at MIC has a high pod-yield under S. rolfsii infestation, demonstrating green chemistry and sustainability of the nanoproduct.

Osmotolerance as a determinant of microbial ecology: A study of phylogenetically diverse fungi

Osmotic stress induced by high solute concentration can prevent fungal metabolism and growth due to alterations in properties of the cytosol, changes in turgor, and the energy required to synthesize and retain compatible solutes. We used germination to quantify tolerance/sensitivity to the osmolyte KCl (0.1-4.5 M, in 0.1 M increments) for 71 strains (40 species) of ecologically diverse fungi. These include 11 saprotrophic species (17 strains, including two xerophilic species), five mycoparasitic species (five strains), six plant-pathogenic species (13 strains), and 19 entomopathogenic species (36 strains). A dendrogram obtained from cluster analyses, based on KCl inhibitory concentrations 50 % and 90 % calculated by Probit Analysis, revealed three groups of fungal isolates accordingly to their osmotolerance. The most-osmotolerant group (Group 3) contained the majority of saprotrophic fungi, and Aspergillus niger (F19) was the most tolerant. The highly xerophilic Aspergillus montevidense and Aspergillus pseudoglaucus were the second- and third-most tolerant species, respectively. All Aspergillus and Cladosporium species belonged to Group 3, followed by the entomopathogens Colletotrichum fioriniae, Simplicillium lanosoniveum, and Trichothecium roseum. Group 2 exhibited a moderate osmotolerance, and included plant-pathogens such as Colletotrichum and Fusarium, mycoparasites such as Clonostachys spp, some saprotrophs such as Mucor and Penicillium spp., and some entomopathogens such as Isaria, Lecanicillium, Mariannaea, Simplicillium, and Torrubiella. Group 1 contained the osmo-sensitive strains: the rest of the entomopathogens and the mycoparasitic Gliocladium and Trichoderma. Although stress tolerance did not correlate with their primary ecological niche, classification of these 71 fungal strains was more closely aligned with their ecology than with their phylogenetic relatedness. We discuss the implications for both microbial ecology and fungal taxonomy.