Bioprospecting the roles of Trichoderma in alleviating plants' drought tolerance: Principles, mechanisms of action, and prospects

Drought-induced stress represents a significant challenge to agricultural production, exerting adverse effects on both plant growth and overall productivity. Therefore, the exploration of innovative long-term approaches for addressing drought stress within agriculture constitutes a crucial objective, given its vital role in enhancing food security. This article explores the potential use of Trichoderma, a well-known genus of plant growth-promoting fungi, to enhance plant tolerance to drought stress. Trichoderma species have shown remarkable potential for enhancing plant growth, inducing systemic resistance, and ameliorating the adverse impacts of drought stress on plants through the modulation of morphological, physiological, biochemical, and molecular characteristics. In conclusion, the exploitation of Trichoderma's potential as a sustainable solution to enhance plant drought tolerance is a promising avenue for addressing the challenges posed by the changing climate. The manifold advantages of Trichoderma in promoting plant growth and alleviating the effects of drought stress underscore their pivotal role in fostering sustainable agricultural practices and enhancing food security.

Trichoderma guizhouense NJAU4742 augments morphophysiological responses, nutrient availability and photosynthetic efficacy of ornamental Ilex verticillata

Winterberry holly (Ilex verticillata [L.] A. Gray), a deciduous shrub producing glossy bright red berries, is a valuable ornamental and medicinal plant with good market prospects. However, the growth and development of I. verticillata are significantly affected by various stresses, and environmentally hazardous agrochemicals are often used to mitigate them. Trichoderma spp., ubiquitous soil-borne eco-friendly plant growth-promoting fungi, are potent biostimulants and biofertilizers and viable alternatives to agrochemicals for healthy and sustainable agriculture. In this study, the temporal efficacy of different dosages of the filamentous fungus Trichoderma guizhouense NJAU4742 in promoting morphophysiological responses of I. verticillata and the physicochemical properties and enzymatic activities of the substrate were investigated. Different concentrations of the strain T. guizhouense NJAU4742 spore suspension (C [0%], T1 [5%, v/m], T2 [10%, v/m] and T3 [15%, v/m]) were injected in the substrate contained in a pot in which 1-year-old I. verticillata was planted for temporal treatment (15, 45 and 75 days) under open-air conditions. The beneficial effects of T2 and/or T3 treatment for a long duration (75 days) were evident on the different root, aerial and photosynthetic traits; total contents of nitrogen (N), phosphorus (P) and potassium (K) in different tissues and the physicochemical properties of the substrate and its enzymatic activities (urease and invertase). Overall, the study revealed the potency of strain T. guizhouense NJAU4742 as a sustainable solution to improve the growth and development and ornamental value of I. verticillata.

Antagonistic activity of Trichoderma asperellum against Fusarium species, chemical profile and their efficacy for management of Fusarium-root rot disease in dry bean

BACKGROUND

Diseases caused by Fusarium pathogens lead to significant yield losses on many economically important crops. The purpose of this study was to evaluate the antagonistic capability and chemical profile of the bioagent Trichoderma asperellum against several Fusarium strains. The efficacy of this strain in reducing Fusarium-root rot disease in dry bean was also examined.

RESULTS

The T. asperellum strain was identified based on sequencing the internal transcribed spacer (ITS) and tef1 gen regions of ribosomal DNA. Dual cultural assay demonstrated their antagonistic activity against the studied Fusarium strains due to the probable combination of competition, mycoparasitism and antibiosis. This strain was positive for cellulase, chitinase and protease activity. The crude extracts of T. asperellum significantly suppressed the growth of the tested Fusarium strains with inhibition zone values ranging from 7.3 to 19.7 mm and minimum inhibitory concentration (MIC) values ranging from 0.15 to 1.42 mg mL-1 . The gas chromatography-mass spectrometry (GC-MS) analysis of cell free supernatant and mycelial biomass of T. asperellum showed the presence of 27 and 21 compounds, respectively. The main compounds responsible for the bioactivity were butylated hydroxytoluene, hexadecanoic acid, 9-octadecenoic acid, ergosterol and hexadecanoic acid, ethyl ester. Trichoderma asperellum significantly increased plant emergence and reduced root rot caused by Fusarium solani in dry bean grown under glasshouse and field trials. Further, plant biomass and dry bean yield were higher in T. asperellum-treated plants than in control plants.

CONCLUSION

Trichoderma asperellum was highly effective, through various mechanisms, against Fusarium strains especially F. solani which causes root rot in dry bean. © 2023 Society of Chemical Industry.

Wastewater irrigation and Trichoderma colonization in tomato plants: effects on plant traits, antioxidant activity, and performance of the insect pest Macrosiphum euphorbiae

The scarcity of freshwater for agriculture in many regions has led to the application of sewage and saline water for irrigation. Irrigation with non-conventional water sources could become a non-harmful process for plant cultivation, and the effects of their use on crops should be monitored in order to develop optimal management strategies. One possibility to overcome potential barriers is to use biostimulants such as Trichoderma spp. fungi. Tomato is a crop of great economic importance in the world. This study investigated the joint effects of Trichoderma afroharzianum T-22 on tomato plants irrigated with simulated unconventional waters. The experiment consisted of a control and three water treatments. In the control, the plants were watered with distilled water. The three water treatments were obtained by using an irrigation water added with nitrogen, a wastewater effluent, and a mixed groundwater-wastewater effluents. Potted tomato plants (variety Bobcat) were grown in a controlled growth chamber. Antioxidant activity, susceptibility to the aphids Macrosiphum euphorbiae, and tomato plant growth parameters were estimated. Trichoderma afroharzianum T-22 had a positive effect on plant growth and antioxidant defenses when plants were irrigated with distilled water. Instead, no significant morphological effects induced by T. afroharzianum T-22 on plants were observed when unconventional water was used for irrigation. However, inoculation with T. afroharzianum T-22 activated a stress response that made the colonized plants more susceptible to aphid development and increased their fecundity and longevity. Thanks to this study, it may be possible for the first time to open a new discussion on the practical possibility of using reclaimed wastewater for crop irrigation with the addition of a growth-promoting fungal symbiont.

Co-inoculation of Soybean Seedling with Trichoderma asperellum and Irpex laceratus Promotes the Absorption of Nitrogen and Phosphorus

Soybean are one of the main oil crops in the world. The study demonstrated that co-inoculation with Trichoderma asperellum (Sordariomycetes, Hypocreomycetidae) and Irpex laceratus (Basidiomycota, Polyporales) isolated from Kosteletzkya virginica can promote the growth of soybean seedlings. The two fungi were found to produce various enzymes, including cellulase, amylase, laccase, protease, and urease. Upon inoculation, T. asperellum mainly colonized within the phloem of the roots in soybean seedlings, while I. laceratus mainly in the xylem and phloem of the roots. Physiological parameters, such as plant height, root length, and fresh weight, were significantly increased in soybean seedlings co-inoculated with T. asperellum and I. laceratus. Moreover, the expression of key genes related to N and P absorption and metabolism was also increased, leading to improved N and P utilization efficiency in soybean seedlings. These results indicate that the two fungi may have complementary roles in promoting plant growth, co-inoculation with T. asperellum and I. laceratus can enhance the growth and nutrient uptake of soybean. These findings suggest that T. asperellum and I. laceratus have the potential to be used as bio-fertilizers to improve soybean growth and yield.

Endophytic colonization of five Trichoderma species and their effects on growth of a Eucalyptus hybrid

The study aimed to evaluate the effectiveness of endophytic colonization via leaf and root inoculation of five Trichoderma species in a Eucalyptus hybrid, as well as the effects of inoculation on plant growth. The experimental design was completely randomized in a 6 × 2 factorial scheme. Plant growth was evaluated during the experimental period at three different times: 20 days after inoculation (d.a.i), 40 d.a.i., and 60 d.a.i. A statistical difference was observed between the inoculation methods during each period and between the Trichoderma species. Plants inoculated with T. asperellum showed the greatest growth among the treatments. Root-inoculated plants produced the greatest growth response. This showed that the presence of Trichoderma in the roots assisted in nutrient assimilation, promoted greater plant growth, when compared with leaf-inoculated plants. Evaluation of the effectiveness of endophytic colonization was performed at each sampling period by collecting leaf samples, and at 60 d.a.i., by collecting leaf, stem, and root samples. T. longibrachiatum and T. harzianum were isolated from leaves at 20 d.a.i., with an increase in the number of colonized plants throughout the evaluation of leaf-inoculated plants. In root-inoculated plants, treatment with T. longibrachiatum, T. harzianum, and T. asperellum presented the highest endophytic colonization in the stem and root samples (at 60 d.a.i.).

Identification of Two Fungal Pathogens Responsible for Liriodendron chinense × tulipifera Black Spot and Screening of Trichoderma sp. for Disease Control

Liriodendron chinense × tulipifera black spot is a newly discovered disease that causes yellowing and early shedding of leaves, affecting the growth of Liriodendron trees, and significantly reducing their ornamental value as a garden species. The pathogen responsible for this disease, and how it can be prevented and controlled, are not clear. In this study, the occurrence of this disease was first investigated according to Koch's postulates, and the primary pathogens causing Liriodendron black spot were determined to be Colletotrichum gloeosporioides and Alternaria alternata. Biocontrol strains antagonistic to these two pathogens were then screened from the leaf microorganisms of L. chinense × tulipifera, and a preliminary investigation of the biological control of Liriodendron black spot was performed. Through the screening of antagonistic microorganisms on the leaf surface of L. chinense × tulipifera, the strain Trichoderma koningiopsis T2, which displayed strong antagonism against C. gloeosporioides and A. alternata, was obtained. The T2 strain could inhibit the growth of the two pathogens via three mechanisms: hyperparasitism, volatile and nonvolatile metabolite production, and environmental acidification. The biocontrol experiments in the greenhouse and field showed that initial spraying with a T. koningiopsis T2 spore suspension followed by the two pathogens resulted in the lowest disease incidence. These results confirmed the black spot pathogens of L. chinense × tulipifera, clarified the antagonistic mechanism of T. koningiopsis T2 against the two pathogens, and provided a theoretical basis and technical support for the biological control of the disease.

Rapid and mass production of biopesticide Trichoderma Brev T069 from cassava peels using newly established solid-state fermentation bioreactor system

Converting agricultural waste into value-added biopesticides to replace chemical pesticides for plant protection is a good alternative for environmental sustainability and resource recycling. In this study, five tropical wastes (cassava peels, banana pseudostem, coconut shell, sugarcane bagasse, and pineapple peels) were screened as substrates for the rapid production of biopesticide Trichoderma Brev T069. Five single tests and a Box-Behnken design (BBD) with response surface methodology were used to optimize the culture conditions to improve the spore yield. The results showed that cassava peel was the optimal solid fermentation substrate, and the optimization enabled a spore yield of 9.31 × 10⁹ spores/g at 3rd day, which was equal to 93.19% of spore yield obtained at 5th day (9.99 × 10⁹ spores/g). A newly packed-bed bioreactor with agitation and ventilation system was developed and used to expand the production that 250 kg of biopesticide (2.89 × 10⁹ spores/g) could be available on the 3rd day. A pot experiment indicated that the biopesticide T. Brev T069 obtained under this production system, when applied at 1 × 10⁷ spores/g of soil had a 64.65% biocontrol efficiency on banana fusarium wilt. This study provides a practical solution for turning a tropical waste into an effective biopesticide which can prevent banana wilt disease, thereby helping to reduce disease management cost and overcome environmental hazards caused by synthetic pesticides.

Synergistic Effects of a Root-Endophytic Trichoderma Fungus and Bacillus on Early Root Colonization and Defense Activation Against Verticillium longisporum in Rapeseed

Rhizosphere-competent microbes often interact with plant roots and exhibit beneficial effects on plant performance. Numerous bacterial and fungal isolates are able to prime host plants for fast adaptive responses against pathogen attacks. Combined action of fungi and bacteria may lead to synergisms exceeding effects of single strains. Individual beneficial fungi and bacteria have been extensively studied in Arabidopsis thaliana, but little is known about their concerted actions in the Brassicaceae. Here, an in-vitro system with oilseed rape (Brassica napus) was established. Roots of two different cultivars were inoculated with well-characterized fungal (Trichoderma harzianum OMG16) and bacterial (Bacillus velezensis FZB42) isolates alone or in combination. Microscopic analysis confirmed that OMG16 hyphae entered root hairs through root hair tips and formed distinct intracellular structures. Quantitative PCR revealed that root colonization of OMG16 increased up to 10-fold in the presence of FZB42. Relative transcript levels of the ethylene- and jasmonic acid-responsive genes PDF1.2, ERF2, and AOC3 were recorded in leaves by quantitative reverse transcription PCR to measure induced systemic resistance in tissues distant from the roots. Combined action of OMG16 and FZB42 induced transcript abundances more efficiently than single inoculation. Importantly, microbial priming reduced Verticillium longisporum root infection in rapeseed by approximately 100-fold compared with nonprimed plants. Priming also led to faster and stronger systemic responses of the defense genes PDF1.2, ERF2, AOC3, and VSP2.[Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Endophytic Trichoderma strains isolated from forest species of the Cerrado-Caatinga ecotone are potential biocontrol agents against crop pathogenic fungi

The indiscriminate use of chemical pesticides increasingly harms the health of living beings and the environment. Thus, biological control carried out by microorganisms has gained prominence, since it consists of an environmentally friendly alternative to the use of pesticides for controlling plant diseases. Herein, we evaluated the potential role of endophytic Trichoderma strains isolated from forest species of the Cerrado-Caatinga ecotone as biological control agents of crop pathogenic fungi. Nineteen Trichoderma strains were used to assess the antagonistic activity by in vitro bioassays against the plant pathogens Colletotrichum truncatum, Lasiodiplodia theobromae, Macrophomina phaseolina, and Sclerotium delphinii isolated from soybean, cacao, fava bean, and black pepper crops, respectively. All Trichoderma strains demonstrated inhibitory activity on pathogen mycelial growth, with maximum percent inhibition of 70% against C. truncatum, 78% against L. theobromae, 78% against M. phaseolina, and 69% against S. delphinii. Crude methanol extracts (0.5 to 2.0 mg mL-1) of Trichoderma strains were able to inhibit the growth of C. truncatum, except Trichoderma sp. T3 (UFPIT06) and T. orientale (UFPIT09 and UFPIT17) at 0.5 mg mL-1, indicating that the endophytes employ a biocontrol mechanism related to antibiosis, together with multiple mechanisms. Discriminant metabolites of Trichoderma extracts were unveiled by liquid chromatography-tandem mass spectrometry-based metabolomics combined with principal component analysis (PCA), which included antifungal metabolites and molecules with other bioactivities. These results highlight the biocontrol potential of Trichoderma strains isolated from the Cerrado-Caatinga ecotone against crop pathogenic fungi, providing support for ongoing research on disease control in agriculture.

Trichoderma: The Current Status of Its Application in Agriculture for the Biocontrol of Fungal Phytopathogens and Stimulation of Plant Growth

Rhizosphere filamentous fungi of the genus Trichoderma, a dominant component of various soil ecosystem mycobiomes, are characterized by the ability to colonize plant roots. Detailed knowledge of the properties of Trichoderma, including metabolic activity and the type of interaction with plants and other microorganisms, can ensure its effective use in agriculture. The growing interest in the application of Trichoderma results from their direct and indirect biocontrol potential against a wide range of soil phytopathogens. They act through various complex mechanisms, such as mycoparasitism, the degradation of pathogen cell walls, competition for nutrients and space, and induction of plant resistance. With the constant exposure of plants to a variety of pathogens, especially filamentous fungi, and the increased resistance of pathogens to chemical pesticides, the main challenge is to develop biological protection alternatives. Among non-pathogenic microorganisms, Trichoderma seems to be the best candidate for use in green technologies due to its wide biofertilization and biostimulatory potential. Most of the species from the genus Trichoderma belong to the plant growth-promoting fungi that produce phytohormones and the 1-aminocyclopropane-1-carboxylate (ACC) deaminase enzyme. In the present review, the current status of Trichoderma is gathered, which is especially relevant in plant growth stimulation and the biocontrol of fungal phytopathogens.

The individual and interactive role of arbuscular mycorrhizal fungi and Trichoderma viride on growth, protein content, amino acids fractionation, and phosphatases enzyme activities of onion plants amended with fish waste

The Green Revolution faced a great cost to meet ever-increasing demands for food, where indiscriminate use of agrochemicals resulted in non-friendly habitats. Therefore, the development of a sustainable approach to better crop production of onion seeds (Allium cepa L.) is very crucial. It is time to use organic waste as a replacement for agrochemicals by using arbuscular mycorrhizal fungi (AMF) and Trichoderma. Fish waste as representative of food waste acts as a leading cause of contamination of the environment. The interaction of AMF and Trichoderma viride on biomass, total soluble protein, mycorrhizal colonization, amino acids, phosphatases and phosphorus and nitrogen contents of onion plants grown in fish waste amended soil was studied. Fish waste has caused a slight increase in onions biomass, total free amino acids, and soluble protein content while with AMF and T. viride dual inoculation more increments were recorded; such increases were related to an increase in mycorrhizal colonization. T. viride application significantly increased the mycorrhizal colonization levels, but these were significantly reduced with waste addition. Analysis of amino acids in plants showed that their concentrations had changed as a result of waste addition combined with AMF and/or T. viride. The effectiveness of fish waste combined with low cost and health/environmental safety leads to a prediction that the introduction of fish waste coupled with fungi will become a more popular feature of agriculture in the future.

Endophytic strains of Trichoderma increase plants' photosynthetic capability

The world faces two enormous challenges that can be met, at least in part and at low cost, by making certain changes in agricultural practices. There is need to produce enough food and fibre for a growing population in the face of adverse climatic trends, and to remove greenhouse gases to avert the worst consequences of global climate change. Improving photosynthetic efficiency of crop plants can help meet both challenges. Fortuitously, when crop plants' roots are colonized by certain root endophytic fungi in the genus Trichoderma, this induces up-regulation of genes and pigments that improve the plants' photosynthesis. Plants under physiological or environmental stress suffer losses in their photosynthetic capability through damage to photosystems and other cellular processes caused by reactive oxygen species (ROS). But certain Trichoderma strains activate biochemical pathways that reduce ROS to less harmful molecules. This and other mechanisms described here make plants more resistant to biotic and abiotic stresses. The net effect of these fungi's residence in plants is to induce greater shoot and root growth, increasing crop yields, which will raise future food production. Furthermore, if photosynthesis rates are increased, more CO₂ will be extracted from the atmosphere, and enhanced plant root growth means that more sequestered C will be transferred to roots and stored in the soil. Reductions in global greenhouse gas levels can be accelerated by giving incentives for climate-friendly carbon farming and carbon cap-and-trade programmes that reward practices transferring carbon from the atmosphere into the soil, also enhancing soil fertility and agricultural production.

Emerging salt marshes as a source of Trichoderma arenarium sp. nov. and other fungal bioeffectors for biosaline agriculture

AIMS

Sustainable agriculture requires effective and safe biofertilizers and biofungicides with low environmental impact. Natural ecosystems that closely resemble the conditions of biosaline agriculture may present a reservoir for fungal strains that can be used as novel bioeffectors.

METHODS AND RESULTS

We isolated a library of fungi from the rhizosphere of three natural halotolerant plants grown in the emerging tidal salt marshes on the south-east coast of China. DNA barcoding of 116 isolates based on the rRNA ITS1 and 2 and other markers (tef1 or rpb2) revealed 38 fungal species, including plant pathogenic (41%), saprotrophic (24%) and mycoparasitic (28%) taxa. The mycoparasitic fungi were mainly species from the hypocrealean genus Trichoderma, including at least four novel phylotypes. Two of them, representing the taxa Trichoderma arenarium sp. nov. (described here) and T. asperelloides, showed antagonistic activity against five phytopathogenic fungi, and significant growth promotion on tomato seedlings under the conditions of saline agriculture.

CONCLUSIONS

Trichoderma spp. of salt marshes play the role of natural biological control in young soil ecosystems with a putatively premature microbiome.

SIGNIFICANCE AND IMPACT OF THE STUDY

The saline soil microbiome is a rich source of halotolerant bioeffectors that can be used in biosaline agriculture.

Anatomical changes induced by isolates of Trichoderma spp. in soybean plants

In the current work we evaluated the anatomical changes induced by T. harzianum and T. asperellum in two soybean cultivars, BRSGO Caiaponia and NA 5909 RG. Soybean production represents a growing market worldwide, and new methods aimed at increasing its productivity and yield are constantly being sought. Fungi of the genus Trichoderma have been widely used in agriculture as a promising alternative for the promotion of plant growth and for biological control of various pathogens. It is known that Trichoderma spp. colonize plant roots, but the anatomical changes that this fungus can cause are still less studied. Experiment was conducted in a greenhouse to collect leaves and soybean roots to perform analysis of growth parameters, enzymatic activity of defense-related enzymes and anatomical changes. It was observed that inoculation of Trichoderma spp. caused anatomical alterations, among them, increase in stomatal index at the abaxial leaf surface, thickness of the root cortex, thickness of adaxial epidermis, mean diameter of the vascular cylinder, thickness of the mesophyll, and thickness of the spongy parenchyma of the soybean plants. These results indicate that the alterations in these factors may be related to the process of plant resistance to pathogens, and better performance against adverse conditions. This study demonstrates that the anatomical study of plants is an important tool to show the effects that are induced by biological control agents.

Plant Cell Wall Changes in Common Wheat Roots as a Result of Their Interaction with Beneficial Fungi of Trichoderma

Plant cell walls play an important role in shaping the defense strategies of plants. This research demonstrates the influence of two differentiators: the lifestyle and properties of the Trichoderma species on cell wall changes in common wheat seedlings. The methodologies used in this investigation include microscopy observations and immunodetection. In this study was shown that the plant cell wall was altered due to its interaction with Trichoderma. The accumulation of lignins and reorganization of pectin were observed. The immunocytochemistry indicated that low methyl-esterified pectins appeared in intercellular spaces. Moreover, it was found that the arabinogalactan protein epitope JIM14 can play a role in the interaction of wheat roots with both the tested Trichoderma strains. Nevertheless, we postulate that modifications, such as the appearance of lignins, rearrangement of low methyl-esterified pectins, and arabinogalactan proteins due to the interaction with Trichoderma show that tested strains can be potentially used in wheat seedlings protection to pathogens.

Mycoremediation effect of Trichoderma harzianum strain T22 combined with ozonation in diesel-contaminated sand

This study aimed to determine the ability of the fungus Trichoderma harzianum strain T22 (Th-T22) to utilize diesel fuel as a carbon source. The potential use of Th-T22 for diesel bioremediation in an artificial soil was tested by inoculating a diesel-sand mixture with a fungal mycelial suspension of Th-T22. Given the ability of ozone to degrade compounds with low biochemical reactivity, the effect of a pre- and post-ozonation was also evaluated. The survival, growth and sporulation of Th-T22 throughout the bioremediation trial were monitored in all the treatments. In the post-ozonation treatments, the biodegradation percentages of diesel removal were 70.16% and 88.35% in Th-T22-inoculated sand treated or untreated with the antibacterial streptomycin, respectively. The results showed that ozonation alone caused good removal efficiencies (41.9%) but it was much more effective if combined with Th-T22 in a post-ozonation regime, whereas pre-ozonation negatively affected the subsequent biodegradation, likely due to its disinfectant and oxidizing effect on Th-T22. The results obtained demonstrated the significant mycoremediation ability of Th-T22 in diesel-contaminated sand and its possible use as a bioremediation agent for diesel spills in polluted sites.

Near-Complete Genomes of Two Trichoderma Species: A Resource for Biological Control of Plant Pathogens

Trichoderma species are widely used to control fungal and nematode diseases of crops. To date, only one complete Trichoderma genome has been sequenced, T. reesei QM6a, a model fungus for industrial enzyme production, while the species or strains used for biological control of plant diseases are only available as draft genomes. Previously, we demonstrated that two Trichoderma strains (T. afroharzianum and T. cyanodichotomus) provide effective control of nematode and fungal plant pathogens. Based on deep sequencing using Illumina and Pacbio platforms, we have assembled high-quality genomes of the above two strains, with contig N₅₀ reaching 4.2 and 1.7 Mbp, respectively, which is greater than those of published draft genomes. The genome data will provide a resource to assist research on the biological control mechanisms of Trichoderma spp.

IPA-1 a Putative Chromatin Remodeler/Helicase-Related Protein of Trichoderma virens Plays Important Roles in Antibiosis Against Rhizoctonia solani and Induction of Arabidopsis Systemic Disease Resistance

Trichoderma spp. are filamentous fungi that colonize plant roots conferring beneficial effects to plants, either indirectly through the induction of their defense systems or directly through the suppression of phytopathogens in the rhizosphere. Transcriptomic analyses of Trichoderma spp. emerged as a powerful method for identifying the molecular events underlying the establishment of this beneficial relationship. Here, we focus on the transcriptomic response of Trichoderma virens during its interaction with Arabidopsis seedlings. The main response of T. virens to cocultivation with Arabidopsis was the repression of gene expression. The biological processes of transport and metabolism of carbohydrates were downregulated, including a set of cell wall-degrading enzymes putatively relevant for root colonization. Repression of such genes reached their basal levels at later times in the interaction, when genes belonging to the biological process of copper ion transport were induced, a necessary process providing copper as a cofactor for cell wall-degrading enzymes with the auxiliary activities class. RNA-Seq analyses showed the induction of a member of the SNF2 family of chromatin remodelers/helicase-related proteins, which was named IPA-1 (increased protection of Arabidopsis-1). Sequence analyses of IPA-1 showed its closest relatives to be members of the Rad5/Rad16 and SNF2 subfamilies; however, it grouped into a different clade. Although deletion of IPA-1 in T. virens did not affect its growth, the antibiotic activity of Δipa-1 culture filtrates against Rhizoctonia solani diminished but it remained unaltered against Botrytis cinerea. Triggering of the plant defense genes in plants treated with Δipa-1 was higher, showing enhanced resistance against Pseudomonas syringae but not against B. cinerea as compared with the wild type.

Microbial inoculation in rice regulates antioxidative reactions and defense related genes to mitigate drought stress

Microbial inoculation in drought challenged rice triggered multipronged steps at enzymatic, non-enzymatic and gene expression level. These multifarious modulations in plants were related to stress tolerance mechanisms. Drought suppressed growth of rice plants but inoculation with Trichoderma, Pseudomonas and their combination minimized the impact of watering regime. Induced PAL gene expression and enzyme activity due to microbial inoculation led to increased accumulation of polyphenolics in plants. Enhanced antioxidant concentration of polyphenolics from microbe inoculated and drought challenged plants showed substantially high values of DPPH, ABTS, Fe-ion reducing power and Fe-ion chelation activity, which established the role of polyphenolic extract as free radical scavengers. Activation of superoxide dismutase that catalyzes superoxide (O2-) and leads to the accumulation of H2O2 was linked with the hypersensitive cell death response in leaves. Microbial inoculation in plants enhanced activity of peroxidase, ascorbate peroxidase, glutathione peroxidase and glutathione reductase enzymes. This has further contributed in reducing ROS burden in plants. Genes of key metabolic pathways including phenylpropanoid (PAL), superoxide dismutation (SODs), H2O2 peroxidation (APX, PO) and oxidative defense response (CAT) were over-expressed due to microbial inoculation. Enhanced expression of OSPiP linked to less-water permeability, drought-adaptation gene DHN and dehydration related stress inducible DREB gene in rice inoculated with microbial inoculants after drought challenge was also reported. The impact of Pseudomonas on gene expression was consistently remained the most prominent. These findings suggested that microbial inoculation directly caused over-expression of genes linked with defense processes in plants challenged with drought stress. Enhanced enzymatic and non-enzymatic antioxidant reactions that helped in minimizing antioxidative load, were the repercussions of enhanced gene expression in microbe inoculated plants. These mechanisms contributed strongly towards stress mitigation. The study demonstrated that microbial inoculants were successful in improving intrinsic biochemical and molecular capabilities of rice plants under stress. Results encouraged us to advocate that the practice of growing plants with microbial inoculants may find strategic place in raising crops under abiotic stressed environments.

Selected isolates of Trichoderma gamsii induce different pathways of systemic resistance in maize upon Fusarium verticillioides challenge

The pink ear rot is one of the most damaging maize diseases, caused by the mycotoxigenic fungal pathogen, Fusarium verticillioides. The application of biological control agents, like antagonistic and/or resistance inducer microorganisms, is an option to reduce fungal infection and kernel contamination in a sustainable and environmentally friendly way. It is well known that Trichoderma species are non-pathogenic fungi able to antagonize plant pathogens and to induce systemic resistance in plants. The present work aimed to verify if Trichoderma spp., applied to maize kernels, affect the plant growth and induce systemic responses to F. verticillioides. Besides, the capability to reduce fumonisin concentration in liquid cultures was investigated. Two T. gamsii (IMO5 and B21), and one T. afroharzianum (B75) isolates, selected both for antagonism and for the ability to reduce root infections, significantly reduced the endophytic development of the stem-inoculated pathogen, compared to the control. The mechanisms of action appeared to be strain-specific, with IMO5 enhancing transcript levels of marker genes of Induced Systemic Resistance (ZmLOX10, ZmAOS, and ZmHPL) while B21 enhancing marker genes of Systemic Acquired Resistance (ZmPR1 and ZmPR5), as evinced by measuring their expression profiles in the leaves. Moreover, IMO5 promoted plant growth, while B21 was able to significantly reduce the fumonisin content in a liquid medium. The results of this work give new evidence that the seed application of T. gamsii is a promising tool for controlling F. verticillioides to be integrated with breeding and the adoption of good agricultural practices.

The role of Trichoderma spp. and silica gel in plant defence mechanisms and insect response in vineyard

Several elicitors, stimulating induced resistance mechanisms, have potential in preventing or mitigating pathogen infections. Some of these compounds, triggering the production of jasmonic acid (JA), a precursor of herbivore-induced plant volatiles, could also play a central role in indirect resistance to pest species, by improving beneficial arthropod performance, and necrotrophic pathogens. In the current work, Trichoderma gamsii/T. asperellum and silica gel treatments - alone and in combination - were studied to evaluate the plant defence mechanism on grapevines (Vitis vinifera L.) by laboratory and field trials. JA production level was measured before and after Plasmopara viticola infection on potted vines. JA production induced by silica gel was higher than that caused by Trichoderma before infection. In Trichoderma-treated plants, JA production increased after P. viticola inoculation. In vineyard field trials, Mymaridae (Hymenoptera: Chalcidoidea) showed higher captures in transparent sticky traps on silica gel-treated plants, in comparison with control. On the other hand, no significant attraction was detected for Ichneumonoidea and other Chalcidoidea in silica gel and T. gamsii/T. asperellum-treated plants. The potential effects of elicitors are discussed, in the frame of attract and reward strategy.

In Vitro and in Planta Evaluation of Trichoderma asperellum TA as a Biocontrol Agent Against Phellinus noxius, the Cause of Brown Root Rot Disease of Trees

Brown root rot (BRR), caused by the white rot fungus Phellinus noxius, is an epidemic disease of diverse broadleaved and coniferous tree species in many tropical and subtropical regions. Flooding and trenching control measures are difficult to implement, and chemical controls can have an adverse impact on ecosystems. Previous studies have provided in vitro evidence for the potential use of Trichoderma spp. for biocontrol of BRR. Here, we analyzed the in vitro antagonistic and mycoparasitic abilities of four Trichoderma spp. isolates against four P. noxius isolates in dual culture and Ficus microcarpa wood blocks. A convenient inoculation system based on root inoculation of a highly susceptible loquat (Eriobotrya japonica) with P. noxius-colonized wheat-oat grains was developed to examine the effect of Trichoderma treatment in planta. Preventive application of Trichoderma asperellum TA, the isolate showing high antagonistic activity in vitro, was effective in preventing and delaying the wilting of P. noxius-inoculated loquat cuttings in greenhouse trials. To understand the specific niche in which T. asperellum TA interacts with P. noxius, KOH-aniline blue fluorescence microscopy was used to investigate the colonization of loquat roots by P. noxius and/or T. asperellum TA. Dilution plating assays were also conducted to quantify Trichoderma populations in the rhizosphere and potting mix. T. asperellum TA was able to robustly establish in the rhizosphere and potting mix but with scarce root penetration limited to the superficial layer. We discuss the timing and strategy for applying antagonistic Trichodema sp. on living trees or in BRR-infested areas for BRR management.

Supplementation of Trichoderma improves the alteration of nutrient allocation and transporter genes expression in rice under nutrient deficiencies

Nutrients are the finite natural resources that are essential for productivity and development of rice and its deficiency causes compromised yield along with reduced immunity against several biotic and abiotic stresses. In this study, the potential of Trichoderma reesei has been investigated as a biofertilizer (BF) to ameliorate nutrient stress in different rice cultivars at physiological, biochemical and molecular levels. The results indicated that cultivar Heena is much more compatible with BF as compared to cultivar Kiran at 50% nutrient limiting condition. Enhancement in physiological attributes and photosynthetic pigments were observed in BF treated Heena seedlings. The localization of biofertilizer in treated roots was further validated by scanning electron micrographs. This result correlated well with the higher levels of Indole acetic acid and Gibberellic acid in biofertilizer treated rice. Similarly, the uptake of micro-nutrients such as Fe, Co, Cu and Mo was found to be 1.4-1.9 fold higher respectively in BF treated Heena seedlings under 50% nutrient deficient condition. Furthermore, different stress ameliorating enzymes Guaiacol peroxidase, Super oxide dismutase, Total Phenolic Content, Phenol Peroxidase, Phenylalanine ammonia lyase and Ascorbate peroxidase in Heena seedlings were also increased by 1.8, 1.4, 1.2, 2.4, 1.2, and 8.3-fold respectively, at 50% nutrient deficient condition. The up-regulation of different micro and macro-nutrients allocation and accumulation; metal tolerance related; auxin synthesis genes in BF treated Heena as compared to 50% nutrient deficient condition was further supported by our findings that the application of biofertilizer efficiently ameliorated the deficiency of nutrients in rice.

Yield parameters and antioxidant compounds of tomato fruit: the role of plant defence inducers with or without Cucumber mosaic virus infection

BACKGROUND

The production of fruit and vegetables rich in health-promoting components in an eco-friendly context represents the winning answer to the world population demand for food. In this study, the effects of different treatments on the yield and fruit chemical characteristics of tomato (Solanum lycopersicum L.) are reported. The treatments included three inducers of plant defence responses (chitosan, Trichoderma harzianum T-22 and Bacillus subtilis QST713) applied alone or before Cucumber mosaic virus infection. Fruit production and antioxidant compounds were investigated by ultrahigh-performance liquid chromatography (UHPLC) and liquid chromatography-tandem mass spectrometry (LC-MS/MS).

RESULTS

Compared to control fruit harvested from untreated and healthy plants, treatment with QST713 increased the fruit number. Furthermore, plant treatments with T22, QST713 and chitosan alone enhanced fruit carotenoids (lutein and β-carotene), ascorbic acid and phenolic acids (caffeoyl glucoside and p-coumaroyl glucoside). In parallel, compared to fruit harvested from only CMV-infected plants, treatments with T22, QST713 and chitosan before CMV enhanced fruit ascorbic acid and flavonoids (quercetin 3-O-xylosyl-rutinoside and rutin).

CONCLUSION

Antioxidant compounds of tomato fruit can increase with the application of the plant defence inducers, thus protecting both the consumer and plant health. © 2019 Society of Chemical Industry.

An effective method of utilizing vegetable waste in the form of carriers for Trichoderma strains with phytosanitary properties

It has been assumed that compost from savoy cabbage and rapeseed straw is a good substrate for discrimination of the reproduction potential of Trichoderma strains. This hypothesis was verified based on a two-stage incubation experiment. The prepared mixture was fermented in a bio-reactor for 11 weeks. In the second experiment, the mature compost was inoculated with four strains of Trichoderma and a spore concentration of 10⁴ and 10⁶, and then incubated for four weeks. The biomass of autogenic fungi reached a maximum of 12.5 mg∙g^-1 DM in the cooling phase. The variability in temperature during composting significantly affected NH₃ emission. The pH of mature compost from cabbage wastes, as a result of the elevated NH₃ emission reached the alkaline range. The survival of the Trichoderma fungi introduced into the alkali substrate was a result of strain sensitivity to the high pH of the compost and to the initial inoculum density. The adaptation potential of Trichoderma harzianum to the alkali milieu depended on the pH stabilization of the substrate by this fungi, provided the spore inoculum density was 10⁶. The strains of Trichoderma atroviride responded negatively, regardless of the inoculum density, to the alkaline pH of the substrate and to self-induced changes in the compost pH.

Plant Growth Promotion and Biocontrol of Pythium ultimum by Saline Tolerant Trichoderma Isolates under Salinity Stress

This present study evaluates three isolates of Trichoderma as plant growth promoting or biological control agents: Trichoderma aggressivum f. sp. europaeum, Trichoderma saturnisporum, and the marine isolate obtained from Posidonia oceanica, Trichoderma longibrachiatum. The purpose is to contribute to an overall reduction in pesticide residues in the fruit and the environment and to a decrease in chemical fertilizers, the excess of which aggravates one of the most serious abiotic stresses, salinity. The tolerance of the different isolates to increasing concentrations of sodium chloride was evaluated in vitro, as well as their antagonistic capacity against Pythium ultimum. The plant growth promoting capacity and effects of Trichoderma strains on the severity of P. ultimum on melon seedlings under saline conditions were also analysed. The results reveal that the three isolates of Trichoderma, regardless of their origin, alleviate the stress produced by salinity, resulting in larger plants with an air-dry weight percentage above 80% in saline stress conditions for T. longibrachiatum, or an increase in root-dry weight close to 50% when T. aggressivum f. sp. europaeum was applied. Likewise, the three isolates showed antagonistic activity against P. ultimum, reducing the incidence of the disease, with the highest response found for T. longibrachiatum. Biological control of P. ultimum by T. aggressivum f. sp. europaeum and T. saturnisporum is reported for the first time, reducing disease severity by 62.96% and 51.85%, respectively. This is the first description of T. aggressivum f. sp. europaeum as a biological control agent and growth promoter. The application of these isolates can be of enormous benefit to horticultural crops, in both seedbeds and greenhouses.

The Protective Effect of Trichoderma asperellum on Tomato Plants against Fusarium oxysporum and Botrytis cinerea Diseases Involves Inhibition of Reactive Oxygen Species Production

Trichoderma species are fungi widely employed as plant-growth-promoting agents and for biological control. Several commercial and laboratory-made solid formulations for mass production of Trichoderma have been reported. In this study, we evaluated a solid kaolin-based formulation to promote the absortion/retention of Trichoderma asperellum in the substrate for growing tomato plants. The unique implementation of this solid formulation resulted in an increased growth of the tomato plants, both in roots and shoots after 40 days of its application. Plants were challenged with two fungal pathogens, Fusarium oxysporum and Botrytis cinerea, and pretreatment with T. asperellum resulted in less severe wilting and stunting symptoms than non-treated plants. Treatment with T. asperellum formulation inhibited Reactive Oxygen Species (ROS) production in response to the pathogens in comparison to plants that were only challenged with both pathogens. These results suggest that decrease in ROS levels contribute to the protective effects exerted by T. asperellum in tomato.

Characterization of Trichoderma asperellum RM-28 for its sodic/saline-alkali tolerance and plant growth promoting activities to alleviate toxicity of red mud

Red mud (RM) is a highly alkaline, saline and sodic solid by-product released by alumina industries, which pose an economical and environmental problem and establishment of vegetation on these sites is a big challenge. In the present study, a fungus RM-28 exhibiting high tolerance to alkaline (pH 12), saline/sodic (NaCl 4%) was isolated from RM flooded rhizosphere soil of bermudagrass and tested its ability to reduce RM toxicity and promote the growth of sorghum-sudangrass seedlings. This fungus also exhibited high tolerance to heavy metal(loid)s (HMs) and desirable plant growth-promoting traits. This fungus was identified as Trichoderma asperellum based on its internal transcribed spacer (ITS) of rDNA and translation elongation factor-1α (TEF 1α) gene analysis. This fungus was effective in reducing the pH and solubilizing tricalcium phosphate under high alkaline and saline conditions in vitro. Further, RM-28 inoculation significantly lowered the pH and EC of the red mud from 11.8 to 8.2 and 2.23 to 1.42, respectively. Inoculation of RM-28 significantly improved the growth, chlorophyll content and reduced the oxidative stress of sorghum-sudangrass seedlings grown in red mud leachate. These observations suggest that T. asperellum RM-28 serves as potential source for the establishment of vegetation on red mud/red mud contaminated soils.

Application of Trichoderma Strains and Metabolites Enhances Soybean Productivity and Nutrient Content

Trichoderma fungi are effectively marketed worldwide as biocontrol agents and plant biostimulants on numerous crops due to their demonstrated effects in direct antagonism against fungal pathogens and plant growth promotion. Here, we examined the effects of single and combined applications of Trichoderma strains and their bioactive metabolites (BAMs) harzianic acid (HA), 6-pentyl-α-pyrone (6PP), and hydrophobin1 (HYTLO1) on the growth, yield, and nutrient uptake of soybean plants. Significant promotion of plant growth (up to 39%), as well as an increase in mineral content, was achieved with BAMs, used alone or combined with T. harzianum. Interestingly, the treatments also increased the level of fatty acids (oleic, linolenic, 11-eicosenoic, and stearic). This work demonstrates the usefulness of natural compound and microbe combinations to enhance oilseed productivity, and reports for the first time the ability of Trichoderma and/or its BAMs to increase the lipid content in harvested seeds.

Metabolic profiling of Fusarium oxysporum f. sp. conglutinans race 2 in dual cultures with biocontrol agents Bacillus amyloliquefaciens, Pseudomonas aeruginosa, and Trichoderma harzianum

There are increasing efforts to identify biocontrol-active microbial metabolites in order to improve strategies for biocontrol of phytopathogens. In this work, Fusarium oxysporum f. sp. conglutinans was confronted with three different biocontrol agents: Trichoderma harzianum, Bacillus amyloliquefaciens, and Pseudomonas aeruginosa in dual culture bioassays. Metabolites produced during the microbial interactions were screened by a matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). T. harzianum exhibited the strongest inhibition of growth of F. oxysporum resulting in overlay of the pathogen colony with its mycelium. Recorded metabolite profiles suggested a direct attack of F. oxysporum mycelium by T. harzianum and B. amyloliquefaciens by means of membrane-attacking peptaibols and a set of antimicrobial lipopeptides and siderophores, respectively. The direct mode of the biocontrol activity of T. harzianum and B. amyloliquefaciens corresponded to their ability to suppress F. oxysporum production of mycotoxin beauvericin suggesting that this ability is not specific only for Trichoderma species. In the case of P. aeruginosa, siderophores pyoverdine E/D and two rhamnolipids were produced as major bacterial metabolites; the rhamnolipid production was blocked by F. oxysporum. The results showed that this type of biocontrol activity was the least effective against F. oxysporum. The effective application of MALDI-MS profiling to the screening of nonvolatile microbial metabolites produced during the interaction of the phytopathogen and the biocontrol microorganisms was demonstrated.

A new application of Trichoderma asperellum as an anopheline larvicide for eco friendly management in medical science

Microfungal applications are increasing daily in the medical science. Several species of Trichoderma are widely used in agricultural fields as biological control and plant growth promoting agents. The application of Trichoderma asperellum as an entomopathogenic fungus against the Anopheles mosquito, a vector of malaria, is a novel control approach. Controlling malaria with eco-friendly management practices is an urgent need. We isolated three T. asperellum from different natural sources using serial dilution and mosquito baiting techniques. The fungi were identified on the basis of phenotypical and molecular characteristics. The fungi were grown in different natural media to examine spore production ability and the fungal spore suspensions were applied to the anopheline larvae to determine their larvicidal activity in vitro. We investigated the efficacy of crude ME (methanolic extract) and different methanolic fractions (MFs) of the fungal extracts against anopheline larvae. Methanolic Fraction 8 (MF8) exhibited the strongest larvicidal activity. A GC-MS analysis of MF8 and a Chemolibrary search were performed to identify the active agents in the fungal extracts. Among the three isolates of T. asperellum, the TaspSKGN2 isolate showed the lowest LD50 (2.68 × 107 conidia/mL) and LT50 values (12.33 h). The crude ME exhibited LD50 values of 0.073 mg/mL and LT50 values of 11.33 h. MF8 showed LD50 values of 0.059 mg/mL and LT50 values of 8.57 h. In GC-MS study of MF8, 49 compounds were found. Among these, seven compounds (2,3-di hydro thiopene, p-cymene, alpha-pinene, hexadecanoic acid, 8-methyl quinoline, (Z,Z)-9,12-octa decadienoic acid, methyl ester, 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-Pyran-4-one-) with high abundance were found to have insecticidal efficacy by a literature survey. We detected a reduction in the phenoloxidase content inside the cuticle and hemolymph of the anopheline larvae after a few hours of interaction with ME (0.073 mg/mL). Thus Trichoderma asperellum has new applications for the control of Anopheles spp. malaria vectors.

Effect of Trichoderma velutinum and Rhizoctonia solani on the Metabolome of Bean Plants (Phaseolus vulgaris L.)

The common bean (Phaseolus vulgaris L.) is one of the most important food legume crops worldwide that is affected by phytopathogenic fungi such as Rhizoctonia solani. Biological control represents an effective alternative method for the use of conventional synthetic chemical pesticides for crop protection. Trichoderma spp. have been successfully used in agriculture both to control fungal diseases and to promote plant growth. The response of the plant to the invasion of fungi activates defensive resistance responses by inducing the expression of genes and producing secondary metabolites. The purpose of this work was to analyze the changes in the bean metabolome that occur during its interaction with pathogenic (R. solani) and antagonistic (T. velutinum) fungi. In this work, 216 compounds were characterized by liquid chromatography mass spectrometry (LC-MS) analysis but only 36 were noted as significantly different in the interaction in comparison to control plants and they were tentatively characterized. These compounds were classified as: two amino acids, three peptides, one carbohydrate, one glycoside, one fatty acid, two lipids, 17 flavonoids, four phenols and four terpenes. This work is the first attempt to determine how the presence of T. velutinum and/or R. solani affect the defense response of bean plants using untargeted metabolomics analysis.

Enhancement of ligninolytic enzymes production and decolourising activity in Leptosphaerulina sp. by co-cultivation with Trichoderma viride and Aspergillus terreus

This work investigated fungal co-culture as inducer of ligninolytic enzymes and decolourising activity in the Colombian strain Leptosphaerulina sp., an ascomycete white-rot fungus isolated from lignocellulosic material. Aspergillus niger, Aspergillus fumigatus, Aspergillus terreus, Trichoderma viride, Fusarium sp. and Penicillium chrysogenum were tested as Leptosphaerulina sp. inducers. The best fungal combinations in terms of enzyme production, fungal growth and decolourising activity were selected from solid media experiments. Response surface methodology (RSM) was utilised to optimise enzyme production and decolourising activity in liquid media. Solid media assays evidenced T. viride and A. terreus as the best Leptosphaerulina sp. inducers. The RSM identified a triple co-culture inoculated with T. viride (1000 μL) and A. terreus (1000 μL) into a 7-day culture of Leptosphaerulina sp. as the best treatment. This triple combination significantly improved ligninolytic enzymes production and Reactive Black 5 dye removal when compared to the Leptosphaerulina sp. monoculture and previously used chemical inducers. These results demonstrated the potential of fungal co-culture as an environmentally-friendly method to enhance Leptosphaerulina sp. enzymes production and decolourising activity.

Trichoderma harzianum triggers an early and transient burst of nitric oxide and the upregulation of PHYTOGB1 in tomato roots

We recently demonstrated that nitric oxide (NO) accumulation and PHYTOGB1 transcriptional regulation are early components of the regulatory pathway that is activated in tomato roots during the onset of the mycorrhizal symbiosis between Rhizophagus irregularis and tomato roots. We further showed that the mycorrhizal interaction was associated with a specific NO-related signature, different from that triggered by the pathogen Fusarium oxysporum. Here, we extend our investigation by exploring the NO- and PHYTOGB1-related root responses elicited by another root mutualistic endosymbiotic fungus: Trichoderma harzianum T-78. By using T-78 in vitro-grown cultures, we found that T-78 triggered an early and transient burst of NO in tomato roots during the first hours after the interaction. T-78 also elicited the early upregulation of PHYTOGB1, which was maintained during the analyzed timespan. By using glass-house bioassays, we found that in a well-established tomato-T-78 symbiosis, NO root levels were maintained at basal level while PHYTOGB1 expression remained upregulated. Our results demonstrate that the T-78 symbiosis is associated with a rapid and transient burst of NO in the host roots and the transcriptional activation of PHYTOGB1 from early stages of the interaction until the establishment of the symbiosis, most likely to control NO levels and favor the mutualistic symbiosis.

Trichoderma Species: Versatile Plant Symbionts

Because of the need to provide food for the growing population, agricultural activity is faced with the huge challenge of counteracting the negative effects generated by adverse environmental factors and diseases caused by pathogens on crops, while avoiding environmental pollution due to the excessive use of agrochemicals. The exploitation of biological systems that naturally increase plant vigor, preparing them against biotic and abiotic stressors that also promote their growth and productivity represents a useful and viable strategy to help face these challenges. Fungi from the genus Trichoderma have been widely used in agriculture as biocontrol agents because of their mycoparasitic capacity and ability to improve plant health and protection against phytopathogens, which makes it an excellent plant symbiont. The mechanisms employed by Trichoderma include secretion of effector molecules and secondary metabolites that mediate the beneficial interaction of Trichoderma with plants, providing tolerance to biotic and abiotic stresses. Here we discuss the most recent advances in understanding the mechanisms employed by this opportunistic plant symbiont as biocontrol agent and plant growth promoter. In addition, through genome mining we approached a less explored factor that Trichoderma could be using to become successful plant symbionts, the production of phytohormones-auxins, cytokinins, abscisic acid, gibberellins, among others. This approach allowed us to detect sets of genes encoding proteins potentially involved in phytohormone biosynthesis and signaling. We discuss the implications of these findings in the physiology of the fungus and in the establishment of its interaction with plants.

An alternative to mineral phosphorus fertilizers: The combined effects of Trichoderma harzianum and compost on Zea mays, as revealed by 1H NMR and GC-MS metabolomics

The ability of Trichoderma harzianum (strain OMG-08) as plant growth promoting fungus (PGPF), was tested on Zea mays plants grown in soil pots added with different inorganic (triple superphosphate and rock phosphate) and organic (cow and horse manure composts) P fertilizers. The effect of treatments was evaluated by following the variations of plants dry biomass and nutrient content, as well as the metabolic changes in plant leaves by both GC-MS and NMR spectroscopy. A synergic effect was observed in treatments with both composts and fungus inoculation, in which not only plant growth and P uptake were enhanced, but also the expression of different metabolites related to an improved photosynthetic activity. Conversely, the combination of Trichoderma with inorganic fertilizers was less effective and even showed a reduction of plants shoot biomass and N content. The corresponding plant metabolome revealed metabolic compounds typical of biotic or abiotic stresses, which may be attributed to a reduced capacity of inorganic fertilizers to provide a sufficient P availability during plant growth. Our findings also indicate that the molecular composition of compost differentiated the Trichoderma activity in sustaining plant growth. The positive effects of the combined Trichoderma and compost treatment suggest that it may become an alternative to the phosphorus mineral fertilization.

Investigations of Trichoderma spp. and Beauveria bassiana as biological control agent for Xylotrechus arvicola, a major insect pest in Spanish vineyards

Xylotrechus arvicola (Olivier) (Coleoptera: Cerambycidae) is an important pest in vineyards (Vitis vinifera) in the main wine-producing regions of Spain. Effective control of this pest is difficult due to the biology of this pest. Biological control agents (BCAs) have proven to be an effective tool in controlling and preventing the spread of a variety of plant pests and diseases. Consequently, the aim of the present study was to assess the capacity of different Trichodema spp., isolated from various vineyards and one commercial isolate of Beauveria bassiana Vuillemin (Hypocreales: Cordycipitaceae), as BCAs of X. arvicola. Isolates of Trichoderma spp. and one isolate of B. bassiana were evaluated against X. arvicola eggs, larvae and adults. Trichoderma harzianum and Trichoderma gamsii demonstrated a good ovicidal control, 100.0% with T. harzianum and over 92.0% with T. gamsii. These Trichoderma strains achieved an over 65.0% larval mortality and 87.5% adult mortality. B. bassiana was the most effective treatment against X. arvicola larvae. These results confirm that Trichoderma spp. can be used to inhibit egg development. In addition, Trichoderma spp. and B. bassiana can help to prevent larvae boring into vines and to kill adults. Therefore, Trichoderma spp., especially T. harzianum and T. gamsii, and B. bassiana can be considered as highly effective BCAs of X. arvicola in vineyards.

Effect of white mustard cover crop residue, soil chemical fumigation and Trichoderma spp. root treatment on black-foot disease control in grapevine

BACKGROUND

Black-foot disease is one of the main soilborne fungal diseases affecting grapevine production worldwide. Two field experiments were established to evaluate the effect of white mustard cover crop residue amendment and chemical fumigation with propamocarb + fosetyl-Al combined with Trichoderma spp. root treatment on the viability of black-foot inoculum in soil and fungal infection in grafted plants and grapevine seedlings used as bait plants.

RESULTS

A total of 876 black-foot pathogen isolates were collected from grafted plants and grapevine seedlings used as bait plants in both fields. White mustard biofumigation reduced inoculum of Dactylonectria torresensis and the incidence and severity of black-foot of grapevine, but no added benefit was obtained when biofumigation was used with Trichoderma spp. root treatments. The effect of white mustard residues and chemical fumigation on populations of D. torresensis propagules in soil was inconsistent, possibly because of varying pretreatment inoculum levels.

CONCLUSION

Biofumigation with white mustard plants has potential for improving control of black-foot disease in grapevines. This control strategy can reduce soil inoculum levels and protect young plants from infection, providing grape growers and nursery propagators with more tools for developing integrated and sustainable control systems. © 2018 Society of Chemical Industry.

Danger signals activate a putative innate immune system during regeneration in a filamentous fungus

The ability to respond to injury is a biological process shared by organisms of different kingdoms that can even result in complete regeneration of a part or structure that was lost. Due to their immobility, multicellular fungi are prey to various predators and are therefore constantly exposed to mechanical damage. Nevertheless, our current knowledge of how fungi respond to injury is scarce. Here we show that activation of injury responses and hyphal regeneration in the filamentous fungus Trichoderma atroviride relies on the detection of two danger or alarm signals. As an early response to injury, we detected a transient increase in cytosolic free calcium ([Ca²⁺]_c) that was promoted by extracellular ATP, and which is likely regulated by a mechanism of calcium-induced calcium-release. In addition, we demonstrate that the mitogen activated protein kinase Tmk1 plays a key role in hyphal regeneration. Calcium- and Tmk1-mediated signaling cascades activated major transcriptional changes early following injury, including induction of a set of regeneration associated genes related to cell signaling, stress responses, transcription regulation, ribosome biogenesis/translation, replication and DNA repair. Interestingly, we uncovered the activation of a putative fungal innate immune response, including the involvement of HET domain genes, known to participate in programmed cell death. Our work shows that fungi and animals share danger-signals, signaling cascades, and the activation of the expression of genes related to immunity after injury, which are likely the result of convergent evolution.

The idea of regenerating lost body parts has always fascinated humans due to its impact on human health. Recently, the study of the response to damage has gained importance not only in regenerative medicine, but also in organ transplantation. We have established a microbial model that given its relative simplicity and ease to work with, promises to accelerate the advance of our understanding of damage responses and regeneration. We show that activation of injury responses and hyphal regeneration in a filamentous fungus relies on the detection of danger (also called alarm) signals also used by plants and animals. Finally, we discovered a set of genes that become active in response to injury, including those putatively participating in the immune response.

Trichoderma gamsii affected herbivore feeding behaviour on Arabidopsis thaliana by modifying the leaf metabolome and phytohormones

Plants can re-programme their transcriptome, proteome and metabolome to deal with environmental and biotic stress. It has been shown that the rhizosphere microbiome has influence on the plant metabolome and on herbivore behaviour. In the present study, Trichoderma gamsii was isolated from Arabidopsis thaliana rhizosphere soil. The inoculation of roots of Arabidopsis thaliana with T. gamsii significantly inhibited the feeding behaviour of Trichoplusia ni and affected the metabolome as well as the content of phytohormones in Arabidopsis leaves. T. gamsii-treated plant leaves had higher levels of amino acids and lower concentrations of sugars. In addition, T. gamsii-treated plant leaves had more abscisic acid (ABA) and lower levels of salicylic acid (SA) and indole-3-acetic acid (IAA) in comparison with the untreated plants. Furthermore, the inoculation with T. gamsii on different signalling mutants showed that the induction of defences were SA-dependent. These findings indicate that T. gamsii has potential as a new type of biocontrol agent to promote plant repellence to insect attacks.

Root Exudates of Stressed Plants Stimulate and Attract Trichoderma Soil Fungi

Plant roots release complex mixtures of bioactive molecules, including compounds that affect the activity and modify the composition of the rhizosphere microbiome. In this work, we investigated the initial phase of the interaction between tomato and an effective biocontrol strain of Trichoderma harzianum (T22). We found that root exudates (RE), obtained from plants grown in a split-root system and exposed to various biotic and abiotic stress factors (wounding, salt, pathogen attack), were able to stimulate the growth and act as chemoattractants of the biocontrol fungus. On the other hand, some of the treatments did not result in an enhanced chemotropism on Fusarium oxysporum f. sp. lycopersici, indicating a mechanism that may be selective for nonpathogenic microbes. The involvement of peroxidases and oxylipins, both known to be released by roots in response to stress, was demonstrated by using RE fractions containing these molecules or their commercial purified analogs, testing the effect of an inhibitor, and characterizing the complex pattern of these metabolites released by tomato roots both locally and systemically.

The Hydrophobin HYTLO1 Secreted by the Biocontrol Fungus Trichoderma longibrachiatum Triggers a NAADP-Mediated Calcium Signalling Pathway in Lotus japonicus

Trichoderma filamentous fungi are increasingly used as biocontrol agents and plant biostimulants. Growing evidence indicates that part of the beneficial effects is mediated by the activity of fungal metabolites on the plant host. We have investigated the mechanism of plant perception of HYTLO1, a hydrophobin abundantly secreted by Trichoderma longibrachiatum, which may play an important role in the early stages of the plant-fungus interaction. Aequorin-expressing Lotus japonicus suspension cell cultures responded to HYTLO1 with a rapid cytosolic Ca2+ increase that dissipated within 30 min, followed by the activation of the defence-related genes MPK3, WRK33, and CP450. The Ca2+-dependence of these gene expression was demonstrated by using the extracellular Ca2+ chelator EGTA and Ned-19, a potent inhibitor of the nicotinic acid adenine dinucleotide phosphate (NAADP) receptor in animal cells, which effectively blocked the HYTLO1-induced Ca2+ elevation. Immunocytochemical analyses showed the localization of the fungal hydrophobin at the plant cell surface, where it forms a protein film covering the plant cell wall. Our data demonstrate the Ca2+-mediated perception by plant cells of a key metabolite secreted by a biocontrol fungus, and provide the first evidence of the involvement of NAADP-gated Ca2+ release in a signalling pathway triggered by a biotic stimulus.

Biochemical mechanism of phytoremediation process of lead and cadmium pollution with Mucor circinelloides and Trichoderma asperellum

This study focused on the bioremediation mechanisms of lead (0, 100, 500, 1000 mg kg^-1) and cadmium (0,10,50,100 mg kg^-1) contaminated soil using two indigenous fungi selected from mine tailings as the phytostimulation of Arabidopsis thaliana. The two fungal strains were characterized as Mucor circinelloides (MC) and Trichoderma asperellum (TA) by internal transcribed spacer sequencing at the genetic levels. Our research revealed that Cadmium was more toxic to plant growth than lead and meanwhile, MC and TA can strengthen A. thaliana tolerance to cadmium and lead with 40.19-117.50% higher root length and 58.31-154.14% shoot fresh weight of plant compared to non-inoculation. In this study, TA exhibited a higher potential to the inactivation of cadmium; however, MC was more effective in lead passivation. There was a direct correlation between the type of fungi, heavy metal content, heavy metal type and oxidative damage in plant. Both lead and cadmium induced oxidative damage as indicated by increased superoxide dismutase and catalase activities, while the antioxidant levels were significantly higher in fungal inoculated plants compared with those non-inoculated. The analysis of soil enzyme activity and taxonomic richness uncovered that the dominant structures of soil microbial community were altered by exogenous microbial agents. MC enhanced higher microbial diversity and soil enzyme activity than TA. The two indigenous fungi lessened several limiting factors with respect to phytoremediation technology, such as soil chemistry, contamination level and transformation, and metal solubility.

Trichoderma polysporum selectively inhibits white-nose syndrome fungal pathogen Pseudogymnoascus destructans amidst soil microbes

BACKGROUND

Pseudogymnoascus destructans (Pd), the causative fungal agent of white-nose syndrome (WNS), has led to the deaths of millions of hibernating bats in the United States of America (USA) and Canada. Efficient strategies are needed to decontaminate Pd from the bat hibernacula to interrupt the disease transmission cycle without affecting the native microbes. Previously, we discovered a novel Trichoderma polysporum (Tp) strain (WPM 39143), which inhibited the growth of Pd in autoclaved soil samples. In the present investigation, we used culture-based approaches to determine Tp-induced killing of native and enriched Pd in the natural soil of two bat hibernacula. We also assessed the impact of Tp treatment on native microbial communities by metagenomics.

RESULTS

Our results demonstrated that Tp at the concentration of 105 conidia/g soil caused 100% killing of native Pd in culture within 5 weeks of incubation. A 10-fold higher concentration of Tp (106 conidia/g soil) killed an enriched Pd population (105 conidia/g soil). The 12,507 fungal operational taxonomic units (OTUs, dominated by Ascomycota and Basidiomycota) and 27,427 bacterial OTUs (dominated by Acidobacteria and Proteobacteria) comprised the native soil microbes of the two bat hibernacula. No significant differences in fungal and bacterial relative abundances were observed between untreated and Tp-treated soil (105 Tp conidia/g soil, p ≤ 0.05).

CONCLUSIONS

Our results suggest that Tp-induced killing of Pd is highly specific, with minimal to no impact on the indigenous microbes present in the soil samples. These findings provide the scientific rationale for the field trials of Tp in the WNS-affected hibernacula for the effective decontamination of Pd and the control of WNS.

Reduced arsenic availability and plant uptake and improved soil microbial diversity through combined addition of ferrihydrite and Trichoderma asperellum SM-12F1

Arsenic (As) accumulation in agricultural soils is prone to crop uptake, posing risk to human health. Passivation shows potential to inactivate soil labile As and lower crop As uptake but often contributes little to improving the microbiota in As-contaminated soils. Here, the combined addition of ferrihydrite and Trichoderma asperellum SM-12F1 as a potential future application for remediation of As-contaminated soil was studied via pot experiments. The results indicated that, compared with the control treatment, the combined addition of ferrihydrite and T. asperellum SM-12F1 significantly increased water spinach shoot and root biomass by 134 and 138%, respectively, and lowered As content in shoot and root by 37 and 34%, respectively. Soil available As decreased by 40% after the combined addition. The variances in soil pH and As fractionation and speciation were responsible for the changes in soil As availability. Importantly, the combined addition greatly increased the total phospholipid fatty acids (PLFAs) and gram-positive (G+), gram-negative (G-), actinobacterial, bacterial, fungal PLFAs by 114, 68, 276, 292, 133, and 626%, respectively, compared with the control treatment. Correspondingly, the soil enzyme activities closely associated with carbon, nitrogen, and phosphorus mineralization and antioxidant activity were improved. The combination of ferrihydrite and T. asperellum SM-12F1 in soils did not reduce their independent effects.

Massive lateral transfer of genes encoding plant cell wall-degrading enzymes to the mycoparasitic fungus Trichoderma from its plant-associated hosts

Unlike most other fungi, molds of the genus Trichoderma (Hypocreales, Ascomycota) are aggressive parasites of other fungi and efficient decomposers of plant biomass. Although nutritional shifts are common among hypocrealean fungi, there are no examples of such broad substrate versatility as that observed in Trichoderma. A phylogenomic analysis of 23 hypocrealean fungi (including nine Trichoderma spp. and the related Escovopsis weberi) revealed that the genus Trichoderma has evolved from an ancestor with limited cellulolytic capability that fed on either fungi or arthropods. The evolutionary analysis of Trichoderma genes encoding plant cell wall-degrading carbohydrate-active enzymes and auxiliary proteins (pcwdCAZome, 122 gene families) based on a gene tree / species tree reconciliation demonstrated that the formation of the genus was accompanied by an unprecedented extent of lateral gene transfer (LGT). Nearly one-half of the genes in Trichoderma pcwdCAZome (41%) were obtained via LGT from plant-associated filamentous fungi belonging to different classes of Ascomycota, while no LGT was observed from other potential donors. In addition to the ability to feed on unrelated fungi (such as Basidiomycota), we also showed that Trichoderma is capable of endoparasitism on a broad range of Ascomycota, including extant LGT donors. This phenomenon was not observed in E. weberi and rarely in other mycoparasitic hypocrealean fungi. Thus, our study suggests that LGT is linked to the ability of Trichoderma to parasitize taxonomically related fungi (up to adelphoparasitism in strict sense). This may have allowed primarily mycotrophic Trichoderma fungi to evolve into decomposers of plant biomass.

Individual fungi rely on particular host organisms or substrates for their nutrition. Therefore, the genomes of fungi feeding on plant biomass necessarily contain genes encoding plant cell wall-degrading enzymes, while animal parasites may depend on proteolytic activity. Molds in the genus Trichoderma (Ascomycota) display a unique nutritional versatility. They can feed on other fungi, attack animals, and degrade plant debris. The later property is so efficient that one species (T. reesei) is commercially used for the production of cellulolytic enzymes required for making biofuels and other industry. In this work, we have investigated the evolution of proteins required for plant cell wall degradation in nine Trichoderma genomes and found an unprecedented number of lateral gene transfer (LGT) events for genes encoding these enzymes. Interestingly, the transfers specifically occurred from Ascomycota molds that feed on plants. We detected no cases of LGT from other fungi (e.g., mushrooms or wood-rotting fungi from Basidiomycota) that are frequent hosts of Trichoderma. Therefore, we propose that LGT may be linked to the ability of Trichoderma to parasitize on related organisms. This is a characteristic ecological trait that distinguishes Trichoderma from other mycoparasitic fungi. In this report, we demonstrate that the lateral transfer of genes may result in a profound nutritional expansion and contribute to the emergence of a generalist capable of feeding on organic matter of any origin.

Does co-inoculation of Lactuca serriola with endophytic and arbuscular mycorrhizal fungi improve plant growth in a polluted environment?

Phytoremediation of polluted sites can be improved by co-inoculation with mycorrhizal and endophytic fungi. In this study, the effects of single- and co-inoculation of Lactuca serriola with an arbuscular mycorrhizal (AM) fungus, Rhizoglomus intraradices, and endophytic fungi, Mucor sp. or Trichoderma asperellum, on plant growth, vitality, toxic metal accumulation, sesquiterpene lactone production and flavonoid concentration in the presence of toxic metals were evaluated. Inoculation with the AM fungus increased biomass yield of the plants grown on non-polluted and polluted substrate. Co-inoculation with the AM fungus and Mucor sp. resulted in increased biomass yield of plants cultivated on the polluted substrate, whereas co-inoculation with T. asperellum and the AM fungus increased plant biomass on the non-polluted substrate. In the presence of Mucor sp., mycorrhizal colonization and arbuscule richness were increased in the non-polluted substrate. Co-inoculation with the AM fungus and Mucor sp. increased Zn concentration in leaves and roots. The concentration of sesquiterpene lactones in plant leaves was decreased by AM fungus inoculation in both substrates. Despite enhanced host plant costs caused by maintaining symbiosis with numerous microorganisms, interaction of wild lettuce with both mycorrhizal and endophytic fungi was more beneficial than that with a single fungus. The study shows the potential of double inoculation in unfavourable environments, including agricultural areas and toxic metal-polluted areas.

The effect of lyophilization and storage time on the survival rate and hydrolytic activity of Trichoderma strains

The study evaluates the survivability and storage stability of seven Trichoderma strains belonging to the species: T. harzianum (1), T. atroviride (4), and T. virens (2) after the lyophilization of their solid state cultures on wheat straw. Biomass of Trichoderma strains was freeze-dried with and without the addition of maltodextrin. Furthermore, in order to determine the ability of tested Trichoderma strains to preserve selected technological features, the biosynthesis of extracellular hydrolases (cellulases, xylanases, and polygalacturonases) after a 3-month storage of lyophilizates was investigated. Strains of T. atroviride (except TRS40) and T. harzianum TRS85 showed the highest viability after lyophilization process (up to 100%). After 3 months of storage, T. atroviride TRS14 exhibited the highest stability (95.23%); however, the number of active conidia remained at high level of 10⁶–10⁷ cfu/g for all tested T. atroviride strains and T. harzianum TRS85. Interestingly, after a 3-month storage of lyophilized formulations, most of the tested Trichoderma strains exhibited higher cellulolytic and xylanolytic activities compared to the control, i.e., before freeze-drying process. The highest activities of these enzymes exhibited the following: T. atroviride TRS14–2.37 U/g and T. atroviride TRS25–21.47 U/g, respectively, whereas pectinolytic activity was weak for all tested strains, with the highest value of 0.64 U/g registered for T. virens TRS109.

Trichoderma harzianum enhances tomato indirect defense against aphids

Many fungal root symbionts of the genus Trichoderma are well-known for their beneficial effects on agronomic performance and protection against plant pathogens; moreover, they may enhance protection from insect pests, by triggering plant resistance mechanisms. Defense barriers against insects are induced by the activation of metabolic pathways involved in the production of defense-related plant compounds, either directly active against herbivore insects, or exerting an indirect effect, by increasing the attraction of herbivore natural enemies. In a model system composed of the tomato plant, the aphid Macrosiphum euphorbiae and the parasitoid Aphidius ervi, plant metabolic changes induced by Trichoderma harzianum and their effects on higher trophic levels have been assessed. T. harzianum T22 treatments induce a primed state that upon aphid attacks leads to an increased attraction of aphid parasitoids, mediated by the enhanced production of volatile organic compounds (VOCs) that are known to induce Aphidius ervi flight. Transcriptome sequencing of T22-treated plants infested by aphids showed a remarkable upregulation of genes involved in terpenoids biosynthesis and salicylic acid pathway, which are consistent with the observed flight response of A. ervi and the VOC bouquet profile underlying this behavioral response.