Trichoderma asperellum Secreted 6-Pentyl-α-Pyrone to Control Magnaporthiopsis maydis, the Maize Late Wilt Disease Agent

Linking a polyketide synthase gene cluster to 6-pentyl-alpha-pyrone, a Trichoderma metabolite with diverse bioactivities

BACKGROUND

Members of the fungal genus Trichoderma are well-known for their mycoparasitic and plant protecting activities, rendering them important biocontrol agents. One of the most significant specialized metabolites (SMs) produced by various Trichoderma species is the unsaturated lactone 6-pentyl-alpha-pyrone (6-PP). Although first identified more than 50 years ago and having pronounced antifungal and plant growth-promoting properties, the biosynthetic pathway of 6-PP still remains unresolved.

RESULTS

Here, we demonstrate that 6-PP is biosynthesized via the polyketide biosynthesis pathway. We identified Pks1, an iterative type I polyketide synthase, as crucial for its biosynthesis in Trichoderma atroviride, a species recognized for its prominent 6-PP production abilities. Phylogenetic and comparative genomic analyses revealed that the pks1 gene is part of a biosynthetic gene cluster conserved in those Trichoderma species that are known to produce 6-PP. Deletion of pks1 caused a complete loss of 6-PP production in T. atroviride and a significant reduction in antifungal activity against Botrytis cinerea and Rhizoctonia solani. Surprisingly, the absence of pks1 led to enhanced lateral root formation in Arabidopsis thaliana during interaction with T. atroviride. Transcriptomic analysis revealed co-regulation of pks1 with adjacent genes, including candidates coding for a C3H1-type zinc finger protein and lytic polysaccharide monooxygenase, suggesting coordination between 6-PP biosynthesis and environmental response mechanisms.

CONCLUSION

Our findings establish pks1 as an essential gene for 6-PP biosynthesis in T. atroviride, providing novel insights into the production of one of the most significant compounds of this mycoparasite. These findings may pave the way for the development of improved biocontrol agents and the application of 6-PP as potent biopesticide contributing to an eco-friendly and sustainable way of plant disease management.

Exploring Endophytic Fungi as Natural Antagonists against Fungal Pathogens of Food Crops

The yield and quality of cultivated food crops are frequently compromised by the prevalent threat from fungal pathogens that can cause widespread damage in both the pre-harvest and post-harvest stages. This paper investigates the challenges posed by fungal pathogens to the sustainability and yield of essential food crops, leading to significant economic and food security repercussions. The paper critiques the long-standing reliance on synthetic fungicides, emphasizing the environmental and health concerns arising from their widespread and occasionally inappropriate use. In response, the paper explores the potential of biological control agents, specifically endophytic fungi in advancing sustainable agricultural practices. Through their diverse symbiotic relationships with host plants, these fungi exhibit strong antagonistic capabilities against phytopathogenic fungi by producing various bioactive compounds and promoting plant growth. The review elaborates on the direct and indirect mechanisms of endophytic antagonism, such as antibiosis, mycoparasitism, induction of host resistance, and competition for resources, which collectively contribute to inhibiting pathogenic fungal growth. This paper consolidates the crucial role of endophytic fungi, i.e., Acremonium, Alternaria, Arthrinium, Aspergillus, Botryosphaeria, Chaetomium, Cladosporium, Cevidencealdinia, Epicoccum, Fusarium, Gliocladium, Muscodor, Nigrospora, Paecilomyces, Penicillium, Phomopsis, Pichia, Pochonia, Pythium, Ramichloridium, Rosellinia, Talaromyces, Trichoderma, Verticillium, Wickerhamomyces, and Xylaria, in biological control, supported by the evidence drawn from more than 200 research publications. The paper pays particular attention to Muscodor, Penicillium, and Trichoderma as prominent antagonists. It also emphasizes the need for future genetic-level research to enhance the application of endophytes in biocontrol strategies aiming to highlight the importance of endophytic fungi in facilitating the transition towards more sustainable and environmentally friendly agricultural systems.

Uncovering the multifaceted properties of 6-pentyl-alpha-pyrone for control of plant pathogens

Some volatile organic compounds (VOCs) produced by microorganisms have the ability to inhibit the growth and development of plant pathogens, induce the activation of plant defenses, and promote plant growth. Among them, 6-pentyl-alpha-pyrone (6-PP), a ketone produced by Trichoderma fungi, has emerged as a focal point of interest. 6-PP has been isolated and characterized from thirteen Trichoderma species and is the main VOC produced, often accounting for >50% of the total VOCs emitted. This review examines abiotic and biotic interactions regulating the production of 6-PP by Trichoderma, and the known effects of 6-PP on plant pathogens through direct and indirect mechanisms including induced systemic resistance. While there are many reports of 6-PP activity against plant pathogens, the vast majority have been from laboratory studies involving only 6-PP and the pathogen, rather than glasshouse or field studies including a host plant in the system. Biopesticides based on 6-PP may well provide an eco-friendly, sustainable management tool for future agricultural production. However, before this can happen, challenges including demonstrating disease control efficacy in the field, developing efficient delivery systems, and determining cost-effective application rates must be overcome before 6-PP's potential for pathogen control can be turned into reality.

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.

6-Pentyl-α-Pyrone from Trichoderma gamsii Exert Antioxidant and Anti-Inflammatory Properties in Lipopolysaccharide-Stimulated Mouse Macrophages

Filamentous fungi produce several beneficial secondary metabolites, including bioactive compounds, food additives, and biofuels. Trichoderma, which is a teleomorphic Hypocrea that falls under the taxonomic groups Ascomycota and Dikarya, is an extensively studied fungal genus. In an ongoing study that seeks to discover bioactive natural products, we investigated potential bioactive metabolites from the methanolic extract of cultured Trichoderma gamsii. Using liquid chromatography-mass spectrometry (LC-MS), one major compound was isolated and structurally identified as 6-pentyl-α-pyrone (6PP) based on nuclear magnetic resonance data and LC-MS analysis. To determine its antioxidant and anti-inflammatory activity, as well as the underlying mechanisms, we treated lipopolysaccharide (LPS)-stimulated Raw264.7 mouse macrophages with 6PP. We found that 6PP suppresses LPS-induced increase in the levels of nitric oxide, a mediator of oxidative stress and inflammation, and restores LPS-mediated depletion of total glutathione by stabilizing nuclear factor erythroid 2-related factor 2 (Nrf2), an antioxidative factor, and elevating heme oxygenase-1 levels. Furthermore, 6PP inhibited LPS-induced production of proinflammatory cytokines, which are, at least in part, regulated by heme oxygenase-1 (HO-1). 6PP suppressed proinflammatory responses by inhibiting the nuclear localization of nuclear factor kappa B (NF-κB), as well as by dephosphorylating the mitogen-activated protein kinases (MAPKs). These results indicate that 6PP can protect macrophages against oxidative stress and LPS-induced excessive inflammatory responses by activating the Nrf2/HO-1 pathway while inhibiting the proinflammatory, NF-κB, and MAPK pathways.

Soil bio-solarization and Trichoderma asperellum suppress black root rot disease and increase strawberry yield.. [DOI: 10.21203/rs.3.rs-3096529/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Trichoderma asperellum applied as pellets, disks, or spore suspension against the causal agents of strawberry-black root rot disease represented by three fungal species was tested. The pellets/disks could significantly reduce the growth area of the pathogenic fungi Rhizoctonia solani, Fusarium solani, and Macrophomina phaseolina in vitro. Solarization via mulching soil with transparent polyethylene sheets could affect these pathogens. It reduced the counts of the fungi buried in cloth bags at 1–10 cm of soil surface by 70, 65, and 65% for R. solani, F. solani, and M. phaseolina, respectively relative to unmulched soil. Yet, the more depths of bags in soil, the less the mulching affects the three pathogens. In two field experiments, the disease incidence and severity were more reduced when T. asperellum pellets/suspension was integrated with bio-solarization (mulching soon after bio-fumigation with Al-Abour Compost®)) than any single treatment. The highest reductions obtained by T. asperellum pellets combined with bio-solarization averaged 75 and 73.8%, respectively. Bio-solarization with Actamyl affected the disease incidence/severity to a lesser extent. All tested treatments significantly boosted yield of strawberry plants. Strawberry yield and activities of the pathogenesis-related proteins peroxidase and chitinase showed favorable responses almost parallel to the extent of reduction in the disease incidence and severity caused by all treatments. The highest yield increase achieved via combining T. asperellum pellets with bio-solarization was 160.8%. Our results support hypothetical biocontrol potential that T. asperellum and bio-solarization together with adequate phytosanitary measures can reliably control strawberry-black root rot disease and enhance strawberry yield.

Comparative physiological and transcriptome analysis provide insights into the inhibitory effect of 6-pentyl-2H-pyran-2-one on Clarireedia jacksonii

Clarireedia spp. is a destructive phytopathogenic fungus that causes turf dollar spot of bent-grass, leading to widespread lawn death. In this study, we explored the antifungal capability of 6-pentyl-2H-pyran-2-one (6PP), a natural metabolite volatilized by microorganisms, which plays an important role in the biological control of turfgrass dollar spot. However, the mechanisms by which 6PP inhibits Clarireedia jacksonii remain unknown. In the present study, C. jacksonii mycelial growth was inhibited by the 6PP treatment and the 6PP treatment damaged cell membrane integrity, causing an increase in relative conduc-tivity. Furthermore, physiological and biochemistry assay showed that 6PP treatment can enhance reactive oxygen species (ROS) levels, malondialdehyde (MDA) content obviously increased with 6PP exposure, increased alchohol dehydrogenase (ADH) and depleted acetalde-hyde dehydrogenase (ALDH), and activated the activities of many antioxidant enzymes in C. jacksonii. Gen Ontology and Kyoto Encyclopedia of Genes and Genomes analysis revealed that some genes in C. jacksonii after 6PP treatment related to integrity of the cell wall and membrane, and oxidative stress were significantly downregulated. It is worth mentioning that the fatty acid degradation pathway is significantly upregulated, with an increase in ATP content and ATP synthase activity, which may promote fungal cell apoptosis. Moreover, we found that the expression of ABC transporters, and glutathione metabolism encoding genes were increased to respond to external stimuli. Taken together, these findings revealed the potential antifungal mechanism of 6PP against Clarireedia spp., which also provides a theoretical basis for the commercial utilization of 6PP as a green pesticide in the future.

Biomolecules in modern and sustainable agriculture

This review presents scientific findings which indicate biomolecules are excellent candidates for the development of biopesticides. Efforts are being done to find routes to increase their concentrations in the cultivation media because this concentration facilitates applications, storage, and transportation. Some of these routes are co-fermentation and ultrasound-assisted fermentation. Ultrasonication increases metabolite production and growth rates by improvement of cell permeability and nutrient uptake rates through cell membranes. For example, 24% increase in the enzymatic activity of cellulases produced by Trichoderma reesei in solid-state fermentation was achieved with ultrasonication. Also, chitinase and β-1,3-glucanase productions were stimulated by ultrasound in Beauveria bassiana cultivation, presenting positive results. The common parameters evaluated in the production of biomolecules by ultrasound-assisted fermentation are the duty cycle, time of application, power, energetic density, and how long the sonication is maintained in the fermentation media. Many successful cases are reported and discussed, which include the final formulation of bioproducts for agricultural applications. In this trend, nanotechnology is a promising tool for the development of nanoformulations. Nanoemulsification, green synthesis, biosynthesis, or biogenic synthesis are technologies used to produce such nanoformulations, allowing the controlled release of control agents, as well as the delivery of biomolecules to specific targets.

Advances in Plant-Pathogen Interaction: New Challenges for Sustainable Disease Management

Plant pathogens cause huge losses and have been an important constraint to a worldwide increase in crop production and productivity [...].

Trichoderma Species: Our Best Fungal Allies in the Biocontrol of Plant Diseases-A Review

Biocontrol agents (BCA) have been an important tool in agriculture to prevent crop losses due to plant pathogens infections and to increase plant food production globally, diminishing the necessity for chemical pesticides and fertilizers and offering a more sustainable and environmentally friendly option. Fungi from the genus Trichoderma are among the most used and studied microorganisms as BCA due to the variety of biocontrol traits, such as parasitism, antibiosis, secondary metabolites (SM) production, and plant defense system induction. Several Trichoderma species are well-known mycoparasites. However, some of those species can antagonize other organisms such as nematodes and plant pests, making this fungus a very versatile BCA. Trichoderma has been used in agriculture as part of innovative bioformulations, either just Trichoderma species or in combination with other plant-beneficial microbes, such as plant growth-promoting bacteria (PGPB). Here, we review the most recent literature regarding the biocontrol studies about six of the most used Trichoderma species, T. atroviride, T. harzianum, T. asperellum, T. virens, T. longibrachiatum, and T. viride, highlighting their biocontrol traits and the use of these fungal genera in Trichoderma-based formulations to control or prevent plant diseases, and their importance as a substitute for chemical pesticides and fertilizers.

Trichoderma and its role in biological control of plant fungal and nematode disease

Trichoderma is mainly used to control soil-borne diseases as well as some leaf and panicle diseases of various plants. Trichoderma can not only prevent diseases but also promotes plant growth, improves nutrient utilization efficiency, enhances plant resistance, and improves agrochemical pollution environment. Trichoderma spp. also behaves as a safe, low-cost, effective, eco-friendly biocontrol agent for different crop species. In this study, we introduced the biological control mechanism of Trichoderma in plant fungal and nematode disease, including competition, antibiosis, antagonism, and mycoparasitism, as well as the mechanism of promoting plant growth and inducing plant systemic resistance between Trichoderma and plants, and expounded on the application and control effects of Trichoderma in the control of various plant fungal and nematode diseases. From an applicative point of view, establishing a diversified application technology for Trichoderma is an important development direction for its role in the sustainable development of agriculture.

Candida species and oral mycobiota of patients clinically diagnosed with oral thrush

Overgrowth of Candida yeasts in the oral cavity may result in the development of oral thrush in immunocompromised individuals. This study analyzed the diversity and richness of the oral mycobiota of patients clinically diagnosed with oral thrush (OT), follow-up of oral thrush patients after antifungal therapy (AT), and healthy controls (HC). Oral rinse and oral swab samples were collected from 38 OT patients, 21 AT patients, and 41 healthy individuals (HC). Pellet from the oral rinse and oral swab were used for the isolation of oral Candida yeasts on Brilliance Candida Agar followed by molecular speciation. ITS1 amplicon sequencing using Illumina MiSeq was performed on DNA extracted from the oral rinse pellet of 16 OT, 7 AT, and 7 HC oral rinse samples. Trimmed sequence data were taxonomically grouped and analyzed using the CLC Microbial Genomics Module workflow. Candida yeasts were isolated at significantly higher rates from oral rinse and swab samples of OT (68.4%, p < 0.001) and AT (61.9%, p = 0.012) patients, as compared to HC (26.8%). Predominance of Candida albicans specifically, was noted in OT (60.5%, p < 0.001) and AT (42.9%, p = 0.006) vs. HC (9.8%), while non-albicans Candida species was dominant in HC. Analysis of oral mycobiota from OT patients showed the presence of 8 phyla, 222 genera, and 309 fungal species. Low alpha diversity (Shannon index, p = 0.006; Chao-1 biased corrected index, p = 0.01), varied beta diversity (Bray-Curtis, p = 0.01986; Jaccard, p = 0.02766; Weighted UniFrac, p = 0.00528), and increased relative abundance of C. albicans (p = 3.18E-02) was significantly associated with the oral mycobiota of OT vs. HC. This study supported that C. albicans is the main etiological agent in oral thrush and highlights the association of fungal biodiversity with the pathophysiology of oral thrush.

Aggressive strains of the late wilt fungus of corn exist in Israel in mixed populations and can specialize in disrupting growth or plant health

Maize late wilt disease caused by the fungus Magnaporthiopsis maydis significantly damages crops in Israel and in other countries. Resistant maize cultivars are the preferred method for disease restraining. However, the pathogen populations of Spain and Egypt have varying aggressiveness, and virulent strains can overcome host resistance. In 2001 and from 2016 to -2019, 17 M. maydis strains were isolated from infected maize fields in Israel. The isolates' effects on seed germination, plant development, and disease symptoms severity were evaluated. The isolates from Israel display a diverse degree of aggressiveness that is not linked to their geographic distribution. The virulent strains are found in mixed populations, whereas less virulent M. maydis isolates exist. Aggressive strains harmed the development of plants and ears and caused severe wilting and death. In contrast, plants inoculated with less virulent strains exhibited only mild dehydration signs, and crop yield was similar to that of the non-infected control. Interestingly, different host cultivars can evoke specific virulence of M. maydis strains. Moreover, some pathogen strains significantly repress plant development, while the impact of other strains was evidenced by wilting symptoms. The current research further increases our understanding of the pathogen and our ability to control it.

Crop Rotation and Minimal Tillage Selectively Affect Maize Growth Promotion under Late Wilt Disease Stress

In recent years, worldwide scientific efforts towards controlling maize late wilt disease (LWD) have focused on eco-friendly approaches that minimize the environmental impact and health risks. This disease is considered to be the most severe threat to maize fields in Israel and Egypt, and a major growth restraint in India, Spain, and Portugal. Today’s most commonly used method for LWD control involving resistant maize genotypes is under constant risk from aggressive pathogen lines. Thus, this study’s objectives were to evaluate the effect of crop rotation and avoiding tillage on restraining the disease. Such an agrotechnical approach will support the continuity of soil mycorrhiza networks, which antagonize the disease’s causal agent, Magnaporthiopsis maydis. The method gained positive results in previous studies, but many knowledge gaps still need to be addressed. To this end, a dual-season study was conducted using the LWD hyper-susceptible maize hybrid, Megaton cv. The trials were performed in a greenhouse and in the field over full dual-growth seasons (wheat or clover as the winter crop followed by maize as the summer crop). In the greenhouse under LWD stress, the results clearly demonstrate the beneficial effect of maize crop rotation with clover and wheat on plant weight (1.4-fold), height (1.1–1.2-fold) and cob yield (1.8–2.4-fold), especially in the no-till soil. The clover-maize growth sequence excels in reducing disease impact (1.7-fold) and pathogen spread in the host tissues (3-fold). Even though the wheat-maize crop cycle was less effective, it still had better results than the commercial mycorrhizal preparation treatment and the uncultivated non-infected soil. The results were slightly different in the field. The clover-maize rotation also achieved the best growth promotion and disease restraint results (2.6-fold increase in healthy plants), but the maize rotation with wheat showed only minor efficiency. Interestingly, pre-cultivating the soil with clover had better results in no-till soil in both experiments. In contrast, the same procedure with wheat had a better impact when tillage was applied. It may be concluded that crop rotation and soil cultivation can be essential in reducing LWD, but other factors may affect this approach’s benefits in commercial field growth.

Control Strategies to Cope with Late Wilt of Maize

Control of maize late wilt disease (LWD) has been at the forefront of research efforts since the discovery of the disease in the 1960s. The disease has become a major economic restraint in highly affected areas such as Egypt and Israel, and is of constant concern in other counties. LWD causes dehydration and collapsing at a late stage of maize cultivation, starting from the male flowering phase. The disease causal agent, Magnaporthiopsis maydis, is a seed- and soil-borne phytoparasitic fungus, penetrating the roots at sprouting, colonizing the vascular system without external symptoms, and spreading upwards in the xylem, eventually blocking the water supply to the plant’s upperparts. Nowadays, the disease’s control relies mostly on identifying and developing resistant maize cultivars. Still, host resistance can be limited because M. maydis undergoes pathogenic variations, and virulent strains can eventually overcome the host immunity. This alarming status is driving researchers to continue to seek other control methods. The current review will summarize the various strategies tested over the years to minimize the disease damage. These options include agricultural (crop rotation, cover crop, no-till, flooding the land before sowing, and balanced soil fertility), physical (solar heating), allelochemical, biological, and chemical interventions. Some of these methods have shown promising success, while others have contributed to our understanding of the disease development and the environmental and host-related factors that have shaped its outcome. The most updated global knowledge about LWD control will be presented, and knowledge gaps and future aims will be discussed.

A Review: Late Wilt of Maize-The Pathogen, the Disease, Current Status, and Future Perspective

Late wilt (LWD) is a vascular wilt disease that outbursts late in maize development, usually during or after flowering. The disease causal agent, the soil and seed-borne fungi, Magnaporthiopsis maydis, causes significant economic losses in Egypt, Israel, Spain, Portugal, and India. Since its discovery in the early 1960s in Egypt, the knowledge base of the disease was significantly expanded. This includes basic information on the pathogen and its mode of action, disease symptoms and damages, methods to study and monitor the pathogen, and above all, control strategies to restrain M. maydis and reduce its impact on commercial maize production. Three approaches stand out from the various control methods inspected. First, the traditional use of chemical pesticides was investigated extensively. This approach gained attention when, in 2018-2020, a feasible and economical treatment based on Azoxystrobin (alone or in combination with other fungicides) was proven to be effective even in severe cases of LWD. Second, the growing trend of replacing chemical treatments with eco-friendly biological and other green protocols has become increasingly important in recent years and has already made significant achievements. Last but not least, today's leading strategy to cope with LWD is to rely on resistant maize genotypes. The past two decades' introduction of molecular-based diagnostic methods to track and identify the pathogen marked significant progress in this global effort. Still, worldwide research efforts are progressing relatively slowly since the disease is considered exotic and unfamiliar in most parts of the world. The current review summarizes the accumulated knowledge on LWD, its causal agent, and the disease implications. An additional important aspect that will be addressed is a future perspective on risks and knowledge gaps.