The entomopathogenic fungus Metarhizium anisopliae enhances Arabidopsis, tomato, and maize plant growth

Identification and optimization of volatile organic compounds to enhance bait attractiveness for red imported fire ants (Solenopsis invicta Buren)

BACKGROUND

The red imported fire ant (RIFA, Solenopsis invicta), a highly destructive invasive pest, has rapidly spread through human trade, posing significant threats to agricultural and forest ecosystems. Due to its preference for high-fat and high-protein foods, ham sausage is commonly used as bait to monitor RIFA populations in invaded areas. However, the presence of volatile organic compounds (VOCs) in such baits may affect their effectiveness because VOCs can act as either attractants or repellents. Identifying VOCs that specifically attract RIFA is essential to improve bait efficacy.

RESULTS

This study aimed to identify attractant compounds within bait VOCs for RIFA, leveraging the highly-expressed antennal odorant-binding protein 1 (OBP1) and reverse chemical ecology approach. Additionally, we examined the effects of mixtures of these attractants on RIFA behavior. Our findings revealed that anethole, 1S-(-)-β-pinene, and β-caryophyllene individually attracted RIFA at 0.1 μg/μL. Notably, a combination of anethole and 1S-(-)-β-pinene enhanced behavioral activity more than individual compounds, suggesting synergistic effects. Conversely, the addition of β-caryophyllene to anethole significantly reduced RIFA activity. These results provide a theoretical basis for developing behavioral regulators targeting RIFA.

CONCLUSION

This study demonstrates that the integration of OBP-based in vitro assays with computational simulations can effectively identify behaviorally active compounds for RIFA. Additionally, it clarifies the optimal ratios of active VOCs in baits, offering valuable theoretical guidance for enhancing RIFA population monitoring efforts. © 2025 Society of Chemical Industry.

Harnessing Fungal Bioagents Rich in Volatile Metabolites for Sustainable Crop Protection: A Critical Review

Pests and diseases have a significant impact on crop health and yields, posing a serious threat to global agriculture. Effective management strategies, such as integrated pest management (IPM), including crop rotation, use of synthetic pesticides, biological control, and resistant/tolerant crop varieties, are essential to mitigate these risks and ensure sustainable agricultural practices. Fungal bioagents play an important role in managing phytopathogens and insect pests by acting as biological agents. They promote healthy plant growth by enhancing the uptake of nutrients and combating systemic resistance in plants. Furthermore, fungal bioagents are environmentally friendly, reducing application of fungicides and insecticides and minimizing their negative impact on the crops and environment. Their use in IPM promotes sustainable agriculture and ensures high-quality crops while maintaining soil health and microbial biodiversity. These fungal bioagents are rich sources of volatile organic compounds (VOCs), which play an important role in biological communication during interaction with insect pests and phytopathogens. In pest management, VOC production by beneficial fungi is accountable for their efficacy against pests and pathogens. Thus, this review discusses the important fungal bioagents producing VOCs, extraction methods of VOC, and the use of VOC-producing fungi in pest and disease management, knowledge gaps, and future research areas.

Endophytic entomopathogenic fungi enhance plant immune responses against tomato leafminer

Plants employ various defense mechanisms to protect themselves from invaders such as microorganisms and herbivores. By recognizing these threats, plants can trigger a cascade of responses throughout their tissues, effectively priming their defenses and enhancing their resistance to future attacks. In this study, we examined the indirect effects of the entomopathogenic fungi Beauveria bassiana strain GHA and Metarhizium anisopliae strain F01 on tomato growth, expression of selected plant genes, production of secondary metabolites, and preference and performance of the tomato leafminer (Tuta absoluta). Both B. bassiana and M. anisopliae colonized tomato endophytically. Plants treated with B. bassiana had greater biomass than the untreated control and M. anisopliae treated plants. Oviposition was lower on plants treated with B. bassiana and M. anisopliae than on untreated controls in both choice and no-choice studies, and both endophytic EPF also affected the development of leafminer larvae. Gene expression analysis of tomato leaves inoculated with endophytic EPF provided evidence of triggering plant immune response genes, and of priming genes for herbivore attack, making plants more resistant to herbivory. These findings provide important insights into the mechanisms by which B. bassiana and M. anisopliae promote tomato plant growth and rapidly respond to T. absoluta infestation by priming the immune system. This knowledge could improve the development of entomopathogenic fungi for use in plant-protection strategies.

Bioinoculant-induced plant resistance is modulated by interactions with resident soil microbes

BACKGROUND

Entomopathogenic fungi are increasingly used as bio-inoculants to enhance crop growth and resistance. When applied to rhizosphere soil, they interact with resident soil microbes, which can affect their ability to colonize and induce resistance in plants as well as modify the structure of the resident soil microbiome, either directly through interactions in the rhizosphere or indirectly, mediated by the plant. The extent to which such direct versus indirect interactions between bio-inoculants and soil microbes impact microbe-induced resistance in crops remains unclear. This study uses a split-root system to examine the effects of direct versus indirect (plant-mediated) interactions between an entomopathogenic fungus, Metarhizium brunneum, and resident soil microbes on induced resistance in tomato against two-spotted spider mites. Additionally, the study explores how these interactions influence the composition and diversity of soil fungal and bacterial communities.

RESULTS

Resident soil microbes reduced the efficacy of M. brunneum to induce resistance against spider mites. This reduction occurred not only when resident microbes directly interacted with the bio-inoculant but also when they were spatially separated within the root system, indicating plant-mediated effects. M. brunneum inoculation did not affect rhizosphere microbial diversity but led to changes in fungal and bacterial community composition, even when these communities were not in direct contact with the inoculant.

CONCLUSIONS

This research highlights the impact of both direct and plant-mediated interactions between bio-inoculants and resident soil microbes on bio-inoculant-induced pest resistance in crop plants and underscores the importance of assessing potential adverse effects of fungal bio-inoculants on native soil communities.

Effects of Marquandomyces marquandii SGSF043 on the Germination Activity of Chinese Cabbage Seeds: Evidence from Phenotypic Indicators, Stress Resistance Indicators, Hormones and Functional Genes

In this study, the effect of Metarhizium spp. M. marquandii on the seed germination of cabbage, a cruciferous crop, was investigated. The effects of this strain on the seed germination vigor, bud growth and physiological characteristics of Chinese cabbage were analyzed by a seed coating method. The results showed the following: (1) The coating agent M. marquandii SGSF043 could significantly improve the germination activity of Chinese cabbage seeds. (2) The strain concentration in the seed coating agent had different degrees of regulation on the antioxidase system of the buds, indicating that it could activate the antioxidant system and improve the antioxidant ability of the buds. (3) When the concentration of M. marquandii SGSF043 was 5.6 × 106 CFU/mL (average per grain), the effect of M. marquandii SGSF043 on the leaf hormones Indole Acetic Acid (IAA), Gibberellic Acid (GA) and Abscisic Acid (ABA) of Chinese cabbage seedlings was significantly higher than that of other treatment groups, indicating that the strain could optimize the level of plant hormones. (4) M. marquandii SGSF043 could induce the expression of stress-resistance-related genes in different tissue parts of Chinese cabbage and improve the growth-promoting stress resistance of buds. This study showed that M. marquandii SGSF043 could not only improve the germination vitality of Chinese cabbage seeds but also enhance the immunity of young buds. The results provide a theoretical basis for the application potential of Metarhizium marquandii in agricultural production.

Evaluation and identification of metabolites produced by Cytobacillus firmus in the interaction with Arabidopsis thaliana plants and their effect on Solanum lycopersicum

Currently, the use of bio-inputs is increasing due to the need to reduce the use of agrochemicals. However, one of the limitations is to preserve the viability of the living microorganisms, so it is important to find an alternative that allows us to obtain different metabolites to produce it. We evaluated three different interactions (contact, diffusible and volatile compounds) in vitro in Arabidopsis thaliana (At) seedlings with the strain Cytobacillus firmus M10 and its filtered secondary metabolites (M10F). The results showed that the seedlings inoculated by contact with the filtrate (AtM10F) presented increases in root length (30 %) and leaf area (33 %), as well as in the volatile interaction (At/M10F) with respect to the uninoculated treatment. For both interactions, the seedlings inoculated with the bacteria by contact (AtM10) and volatile (At/M10) obtained greater biomass (48 and 57 %). Subsequently, an evaluation at the end of the A. thaliana cycle showed that the treatments obtained by contact and distance when reinoculated with the bacteria and the filtrate (AtM10, At-M10 and AtM10F) obtained 50 % more seed yield than the control treatment, while AtM10F presented 72 %, while At/M10F presented the highest no. of siliques and seeds, which increased the yield by 65 %. In the Solanum lycopersicum (Sl) experiment, the filtrate (SlM10F) showed significant differences in seedling height, leaf length and width (23, 24 and 36 %, respectively). It also promoted an increase in fresh and dry weight, producing a greater root area and larger leaves compared to the control (Sl) and the bacteria (SlM10). We performed a qualitative characterization of the secondary metabolites present in the filtrate, where we found 2,4-DTBP, sylvopinol, isophthaladehyde, and eicosane of interest with possible growth-promoting effects on A. thaliana and tomato. We identified volatile compounds present in plant-microorganism and plant-filtrate interactions as possible precursors in the induction of plant growth, among which phenols, alcohols, aldehydes, alkanes, and alkenes stand out. Most of the analyzed compounds have not been found in the literature with reports of growth promoters, is important to mention that due to their characteristic functional groups they can derive and trigger the synthesis of new molecules with agronomic application.

Classification, biology and entomopathogenic fungi-based management and their mode of action against Drosophila species (Diptera: Drosophilidae): a review

This review provides a comprehensive analysis of the classification, biology, and management of Drosophila species (Diptera: Drosophilidae) with a focus on entomopathogenic fungi (EPF) as a biocontrol strategy. Drosophila species, particularly Drosophila suzukii, and Drosophila melanogaster have emerged as significant pests in various agricultural systems, causing extensive damage to fruit crops. Understanding their taxonomic classification and biological traits is crucial for developing effective management strategies. This review delves into the life cycle, behavior, and ecological interactions of Drosophila species, highlighting the challenges posed by their rapid reproduction and adaptability. The review further explores the potential of EPF as an eco-friendly alternative to chemical pesticides. The mode of action of EPF against Drosophila species is examined, including spore adhesion, germination, and penetration of the insect cuticle, leading to host death. Factors influencing the efficacy of EPF, such as environmental conditions, fungal virulence, and host specificity, are discussed in detail. By synthesizing current research, this review aims to provide valuable insights into the application of EPF and to identify future research directions for enhancing the effectiveness of EPF-based control measures against Drosophila species.

Cladosporium psychrotolerans strain T01 enhances plant biomass and also exhibits antifungal activity against pathogens

An increasing number of microorganisms are being identified to enhance plant growth and inhibit phytopathogens. Some Cladosporium species form beneficial associations with plants, either as endophytes or by colonizing the rhizosphere. Herein, we evaluated the influence of the Cladosporium psychrotolerans (T01 strain) fungus on the in vitro growth of Arabidopsis thaliana plantlets through direct and split interactions. After 9 days post-inoculation with C. psychrotolerans, Arabidopsis plantlets exhibited a notable increase in fresh weight and lateral roots, particularly in split interactions. Chlorophyll content increased in both plant-fungus interaction conditions, whereas the primary root was inhibited during direct interaction. We observed an increase in the GUS signal from the Arabidopsis auxin-inducible DR5:uidA marker in lateral root tips in both contact and split fungal interactions, and primary root tips in a split interaction. Arabidopsis and tomato plants cultivated in soil pots and inoculated with C. psychrotolerans (T01 strain) showed a positive effect on biomass production. GC/MS analysis detected that the T01 strain emitted volatile organic compounds (VOCs), predominantly alcohols and aldehydes. These VOCs displayed potent inhibitory effects, with a 60% inhibition against Botrytis cinerea and a 50% inhibition against C. gloeosporioides. Our study demonstrates that C. psychrotolerans T01 has the potential to enhance biomass production and inhibit pathogens, making it a promising candidate for green technology applications.

Root symbiotic fungi improve nitrogen transfer and morpho-physiological performance in Chenopodium quinoa

Root-associated fungal endophytes may facilitate nitrogen (N) absorption in plants, leading to benefits in photosynthesis and growth. Here, we investigated whether endophytic insect pathogenic fungi (EIPF) are capable of transferring soil N to the crop species Chenopodium quinoa. We evaluated nutrient uptake, carbon allocation, and morpho-physiological performance in C. quinoa in symbiosis with two different EIPF (Beauveria and Metarhizium) under contrasting soil N supply. A controlled experiment was conducted using two plant groups: (1) plants subjected to low N level (5 mM urea) and (2) plants subjected to high N level (15 mM urea). Plants from each group were then inoculated with different EIPF strains, either Beauveria (EIPF1+), Metarhizium (EIPF2+) or without fungus (EIPF-). Differences in N and C content, amino acids, proteins, soluble sugars, starch, glutamine synthetase, glutamate dehydrogenase, and physiological (photosynthesis, stomatal conductance, transpiration), and morphological performance between plant groups under each treatment were examined. We found that both Beauveria and Metarhizium translocated N from the soil to the roots of C. quinoa, with positive effects on photosynthesis and plant growth. These effects, however, were differentially affected by fungal strain as well as by N level. Additionally, an improvement in root C and sugar content was observed in presence of EIPF, suggesting translocation of carbohydrates from leaves to roots. Whereas both strains were equally effective in N transfer to roots, Beauveria seemed to exert less demand in C. quinoa for photosynthesis-derived carbohydrates compared to Metarhizium. Our study revealed positive effects of EIPF on N transfer and morpho-physiological performance in crops, highlighting the potential of these fungi as an alternative to chemical fertilizers in agriculture systems.

Entomopathogenic fungi in crops protection with an emphasis on bioactive metabolites and biological activities

Plant pathogens with their abundance are harmful and cause huge damage to different agricultural crops and economy of a country as well as lead towards the shortage of food for humans. For their management, the utilization of entomopathogenic fungi is an eco-friendly technique, sustainable to the environment, safe for humans and has promising effect over chemical-based pesticides. This process requires a biochemical mechanism, including the production of enzymes, toxins, and other metabolites that facilitate host infection and invasion. Essential enzymes such as chitinase, proteinase, and lipase play a direct role in breaking down the host cuticle, the primary barrier to EPF (Entomopathogenic Fungi) infection. Additionally, secondary metabolites such as destruxins in Metarhizium, beauvericin in Beauveria, hirsutellides in Hirsutella, isarolides in Isaria, cordyols in Cordyceps, and vertihemipterins in Verticillium, among others, act both directly and indirectly to disable the defense mechanisms of insect hosts, thereby accelerating the EPF infection process. The chemical composition of these secondary metabolites varies, ranging from simple non-peptide pigments such as oosporine to highly complex piperazine derivatives such as vertihemiptellides. The biocontrol efficacy of EPF is extensively studied, with numerous fungal strains commercially available on a large scale for managing arthropod pests. This review emphasizes the role of proteins and enzymes against crop pathogens, detailing their mode of action, and describing the metabolites from entomopathogenic fungi and their biological activities. In doing so, these findings contribute to establishing a symbiotic equilibrium between agricultural productivity and environmental conservation.

Plant-Entomopathogenic Fungi Interaction: Recent Progress and Future Prospects on Endophytism-Mediated Growth Promotion and Biocontrol

Entomopathogenic fungi, often acknowledged primarily for their insecticidal properties, fulfill diverse roles within ecosystems. These roles encompass endophytism, antagonism against plant diseases, promotion of the growth of plants, and inhabitation of the rhizosphere, occurring both naturally and upon artificial inoculation, as substantiated by a growing body of contemporary research. Numerous studies have highlighted the beneficial aspects of endophytic colonization. This review aims to systematically organize information concerning the direct (nutrient acquisition and production of phytohormones) and indirect (resistance induction, antibiotic and secondary metabolite production, siderophore production, and mitigation of abiotic and biotic stresses) implications of endophytic colonization. Furthermore, a thorough discussion of these mechanisms is provided. Several challenges, including isolation complexities, classification of novel strains, and the impact of terrestrial location, vegetation type, and anthropogenic reluctance to use fungal entomopathogens, have been recognized as hurdles. However, recent advancements in biotechnology within microbial research hold promising solutions to many of these challenges. Ultimately, the current constraints delineate potential future avenues for leveraging endophytic fungal entomopathogens as dual microbial control agents.

The fungal endophyte Metarhizium anisopliae (MetA1) coordinates salt tolerance mechanisms of rice to enhance growth and yield

The implementation of salt stress mitigation strategies aided by microorganisms has the potential to improve crop growth and yield. The endophytic fungus Metarhizium anisopliae shows the ability to enhance plant growth and mitigate diverse forms of abiotic stress. We examined the functions of M. anisopliae isolate MetA1 (MA) in promoting salinity resistance by investigating several morphological, physiological, biochemical, and yield features in rice plants. In vitro evaluation demonstrated that rice seeds primed with MA enhanced the growth features of rice plants exposed to 4, 8, and 12 dS/m of salinity for 15 days in an agar medium. A pot experiment was carried out to evaluate the growth and development of MA-primed rice seeds after exposing them to similar levels of salinity. Results indicated MA priming in rice improved shoot and root biomass, photosynthetic pigment contents, leaf succulence, and leaf relative water content. It also significantly decreased Na+/K+ ratios in both shoots and roots and the levels of electrolyte leakage, malondialdehyde, and hydrogen peroxide, while significantly increasing proline content in the leaves. The antioxidant enzymes catalase, glutathione S-transferase, ascorbate peroxidase, and peroxidase, as well as the non-enzymatic antioxidants phenol and flavonoids, were significantly enhanced in MA-colonized plants when compared with MA-unprimed plants under salt stress. The MA-mediated restriction of salt accumulation and improvement in physiological and biochemical mechanisms ultimately contributed to the yield improvement in salt-exposed rice plants. Our findings suggest the potential use of the MA seed priming strategy to improve salt tolerance in rice and perhaps in other crop plants.

A biostimulant yeast, Hanseniaspora opuntiae, modifies Arabidopsis thaliana root architecture and improves the plant defense response against Botrytis cinerea

MAIN CONCLUSION

The biostimulant Hanseniaspora opuntiae regulates Arabidopsis thaliana root development and resistance to Botrytis cinerea. Beneficial microbes can increase plant nutrient accessibility and uptake, promote abiotic stress tolerance, and enhance disease resistance, while pathogenic microorganisms cause plant disease, affecting cellular homeostasis and leading to cell death in the most critical cases. Commonly, plants use specialized pattern recognition receptors to perceive beneficial or pathogen microorganisms. Although bacteria have been the most studied plant-associated beneficial microbes, the analysis of yeasts is receiving less attention. This study assessed the role of Hanseniaspora opuntiae, a fermentative yeast isolated from cacao musts, during Arabidopsis thaliana growth, development, and defense response to fungal pathogens. We evaluated the A. thaliana-H. opuntiae interaction using direct and indirect in vitro systems. Arabidopsis growth was significantly increased seven days post-inoculation with H. opuntiae during indirect interaction. Moreover, we observed that H. opuntiae cells had a strong auxin-like effect in A. thaliana root development during in vitro interaction. We show that 3-methyl-1-butanol and ethanol are the main volatile compounds produced by H. opuntiae. Subsequently, it was determined that A. thaliana plants inoculated with H. opuntiae have a long-lasting and systemic effect against Botrytis cinerea infection, but independently of auxin, ethylene, salicylic acid, or jasmonic acid pathways. Our results demonstrate that H. opuntiae is an important biostimulant that acts by regulating plant development and pathogen resistance through different hormone-related responses.

Dual role of endophytic entomopathogenic fungi: induce plant growth and control tomato leafminer Phthorimaea absoluta

BACKGROUND

Entomopathogenic fungi (EPF) are multifunctional microorganisms acting not only as biopesticides against insect pests but also as endophytes which regulate plant growth. The tomato leafminer, Phthorimaea absoluta (Tuta absoluta) is a devastating invasive pest of tomatoes worldwide. However, effective alternatives are needed for a sustainable management of this invasive pest. In this study, the functional effects of five EPF isolates Metarhizium flavoviride, M. anisopliae, M. rileyi, Cordyceps fumosorosea and Beauveria bassiana were evaluated on tomato growth promotion and pest protection against P. absoluta.

RESULTS

When directly sprayed with conidia, P. absoluta larvae showed high cumulative mortality of 100% to M. anisopliae under 1 × 108 conidia/mL, whereas M. flavoviride, B. bassiana, C. fumosorosea and M. rileyi caused cumulative mortality of 92.65%, 92.62%, 92.16% and 68.95%, respectively. Moreover, all five EPF isolates can successfully colonize tomato plants, whilst the colonization rate for each EPF depends on the inoculation method used. The most efficient inoculation method for M. flavoviride and M. rileyi was root dipping, for M. anisopliae and C. fumosorosea it was coating seed, and for B. bassiana it was foliage spraying. The highest plant colonization was obtained by M. flavoviride. Meanwhile, all these isolates promoted tomato plant growth upon inoculation. Furthermore, endophytic colonization of plants by the five EPF negatively affected the performance of P. absoluta, among them M. anisopliae and C. fumosorosea showed strong negative effects on the performance of P. absoluta.

CONCLUSION

Our results highlight the potential of incorporating entomopathogenic fungi as endophytes in integrated pest management practices to protect tomatoes against P. absoluta. © 2023 Society of Chemical Industry.

Endophytic insect pathogenic fungi-host plant-herbivore mutualism: elucidating the mechanisms involved in the tripartite interactions

Various techniques used by crop plants to evade insect pests and pathogen attacks have been documented. Among these, plant defense strategies induced by endophytic insect pathogenic fungi are arguably one of the most discussed. Endophytic fungi frequently colonize plants and inhabit their internal tissues for a portion of their lifespan without producing visible symptoms of the disease. This phenomenon is widespread and diverse in both natural and agricultural ecosystems, and is present in almost all plant organs. Many fungi can obtain nutrients by infecting and killing insects, and this ability has been developed numerous times in different fungal lineages. These species mainly consist of those in the order Hypocreales (Ascomycota), where the generalist insect pathogens, Beauveria sp. (Cordycipitaceae) and Metarhizium sp. (Clavicipitaceae) are two of the most studied endophytic entomopathogenic fungal genera. However, most fungi that kill insects do not survive in the tissues of living plants. The data published thus far show a high degree of variability and do not provide consistent explanations for the underlying mechanisms that may be responsible for these effects. This implies that available knowledge regarding the colonization of plant tissues by endophytic insect pathogenic fungi, the effects of colonization on plant metabolism, and how this contributes to a decrease in herbivore and pathogens damage is limited. To adequately utilize fungal-based products as biological control agents, these products must be effective and the reduction of pests and infection must be consistent and similar to that of chemical insecticides after application. This article discusses this possibility and highlights the benefits and the specific techniques utilized by endophytically challenged plants in invading insect pests and disease pathogens.

Metabolite profiling and transcriptomic analyses demonstrate the effects of biocontrol agents on alkaloid accumulation in Fritillaria thunbergii

BACKGROUND

During Fritillaria thunbergii planting, pests and diseases usually invade the plant, resulting in reduced yield and quality. Previous studies have demonstrated that using biocontrol agents can effectively control grubs and affect the steroid alkaloids content in F. thunbergii. However, the molecular regulatory mechanisms underlying the differences in the accumulation of steroid alkaloids in response to biocontrol agents remain unclear.

RESULTS

Combined transcriptomic and metabolic analyses were performed by treating the bulbs of F. thunbergii treated with biocontrol agents during planting. Otherwise, 48 alkaloids including 32 steroid alkaloids, 6 indole alkaloids, 2 scopolamine-type alkaloids, 1 isoquinoline alkaloid, 1 furoquinoline alkaloid, and 6 other alkaloids were identified. The content of steroidal alkaloids particularly peimine, peiminine, and veratramine, increased significantly in the group treated with the biocontrol agents. Transcriptome sequencing identified 929 differential genes using biocontrol agents, including 589 upregulated and 340 downregulated genes. Putative biosynthesis networks of steroid alkaloids have been established and combined with differentially expressed structural unigenes, such as acetyl-CoA C-acetyl-transferase, acelyl-CoAC-acetyltransferase3-hydroxy-3-methylglutaryl-coenzyme A synthase, 1-deoxy-D-xylulose-5-phosphate reductor-isomerase, 2-C-methyl-D-erythritol-4-phosphate cytidylyltransferase and 4-hydroxy-3-methylbut-2-enyl diphosphate reductase. In addition, biological processes such as amino acid accumulation and oxidative phosphorylation were predicted to be related to the synthesis of steroid alkaloids. Cytochrome P450 enzymes also play crucial roles in the steroid alkaloid synthesis. The transcription factor families MYB and bHLH were significantly upregulated after using biocontrol agents.

CONCLUSIONS

Biocontrol agents increased the steroid alkaloids accumulation of steroid alkaloids by affecting key enzymes in the steroid alkaloid synthesis pathway, biological processes of oxidative phosphorylation and amino acid synthesis, cytochrome P450 enzymes, and transcription factors. This study revealed the mechanism underlying the difference in steroidal alkaloids in F. thunbergii after using biocontrol agents, laying the groundwork for future industrial production of steroid alkaloids and ecological planting of medicinal materials in the future.

Fungal Alcohol Dehydrogenases: Physiological Function, Molecular Properties, Regulation of Their Production, and Biotechnological Potential

Fungal alcohol dehydrogenases (ADHs) participate in growth under aerobic or anaerobic conditions, morphogenetic processes, and pathogenesis of diverse fungal genera. These processes are associated with metabolic operation routes related to alcohol, aldehyde, and acid production. The number of ADH enzymes, their metabolic roles, and their functions vary within fungal species. The most studied ADHs are associated with ethanol metabolism, either as fermentative enzymes involved in the production of this alcohol or as oxidative enzymes necessary for the use of ethanol as a carbon source; other enzymes participate in survival under microaerobic conditions. The fast generation of data using genome sequencing provides an excellent opportunity to determine a correlation between the number of ADHs and fungal lifestyle. Therefore, this review aims to summarize the latest knowledge about the importance of ADH enzymes in the physiology and metabolism of fungal cells, as well as their structure, regulation, evolutionary relationships, and biotechnological potential.

Effect of Metarhizium anisopliae (MetA1) on growth enhancement and antioxidative defense mechanism against Rhizoctonia root rot in okra

Rhizoctonia solani is an important necrotrophic pathogenic fungus that causes okra root disease and results in severe yield reduction. Many biocontrol agents are being studied with the intent of improving plant growth and defense systems and reducing crop loss by preventing fungal infections. Recently, a member of the Hypocrealean family, Metarhizium anisopliae, has been reported for insect pathogenicity, endophytism, plant growth promotion, and antifungal potentialities. This research investigated the role of M. anisopliae (MetA1) in growth promotion and root disease suppression in okra. The antagonism against R. solani and the plant growth promotion traits of MetA1 were tested in vitro. The effects of endophytic MetA1 on promoting plant growth and disease suppression were assessed in planta. Dual culture and cell-free culture filtrate assays showed antagonistic activity against R. solani by MetA1. Some plant growth promotion traits, such as phosphate solubilization and catalase activity were also exhibited by MetA1. Seed primed with MetA1 increased the shoot, root, leaves, chlorophyll content, and biomass content compared to control okra plants. The plants challenged with R. solani showed the highest hydrogen peroxide (H2O2) and lipid peroxidation (MDA) contents in the leaves of okra. Whereas MetA1 applied plants showed a reduction of H2O2 and MDA by 5.21 and 14.96%, respectively, under pathogen-inoculated conditions by increasing antioxidant enzyme activities, including catalase (CAT), peroxidase (POD), glutathione S-transferase (GST), and ascorbate peroxidase (APX), by 30.11, 10.19, 5.62, and 5.06%, respectively. Moreover, MetA1 increased soluble sugars, carbohydrates, proline, and secondary metabolites, viz., phenol and flavonoid contents in okra resulting in a better osmotic adjustment of diseases infecting plants. MetA1 reduced disease incidence by 58.33% at 15 DAI compared to the R. solani inoculated plant. The results revealed that MetA1 improved plant growth, elevated the plant defense system, and suppressed root diseases caused by R. solani. Thus, MetA1 was found to be an effective candidate for the biological control program.

Screening of Fungal Strains and Formulations of Metarhizium anisopliae to Control Phyllotreta striolata in Chinese Flowering Cabbage

(1) Background: The cabbage flea beetle (CFB; Phyllotreta striolata) seriously damages the production of Chinese flowering cabbage (CFC; Brassica campestris L. ssp. chinensis var. utilis), which is a key leafy vegetable in South China. A large number of chemical insecticides have been sprayed to control this pest; as a result, residues and resistances are becoming an issue. It is necessary to develop biocontrol technologies to address this issue. (2) Methods: Fungal strains were selected based on bioactivity against CFB, and CFC seed pelletization with fungal conidia was subject to evaluation of control efficacy against CFB. The effective mixture of fungus and chemical insecticide was determined based on safety and joint toxicology tests. (3) Results: The screening of 103 strains from 14 genera identified the Metarhizium anisopliae strain MaGX19S02 (Ma) as the one with the highest virulence. The LC₅₀s of Ma to CFB adult and second instar larvae on day 9 post-treatment were 3.04 × 10⁶ and 27.2 × 10⁶ spores/mL, respectively. In the pot test, the pelletization of CFC seeds with Ma conidia (50/25/12.5 mg in 1 g seed with 4 g fillers) demonstrated significant CFB mortalities (45-82%) 20 days after the larvae were introduced. In the field test, the seed pelletization achieved 57-81% control efficacy 14 days after sowing. Furthermore, the combination of Ma with chlorfenapyr (Chl) demonstrated a synergistic effect against CFB; based on this result, we prepared the mixture formulation of 20% Ma-Chl wettable powder (WP). The assessment of the effects of 20% Ma-Chl WP (500× diluent) against CFB revealed 93.33% mortality in the pot test and 61.3% control efficacy in the field test on day 7 post-treatment. (4) Conclusions: The findings demonstrate the potential of Ma to control CFB in the field. Seed pelletization with Ma conidia effectively controlled CFB larvae and protected CFC seedlings, wherein a mixture formulation of 20% Ma-Chl WP had substantial efficacy in controlling CFB adults. Our research provides new methods for CFB biocontrol.

Light in the box-photobiological examination chamber with light trap ventilation system for studying fungal surface cultures illustrated with Metarhizium brunneum and Beauveria brongniartii

Due to their versatile way of life as saprophytes, endophytes, and entomopathogens, fungi of the genera Metarhizium and Beauveria are exposed to varying illumination conditions in their natural habitats, which makes a thorough adaptation to light very likely. While the few available studies for these genera support this assumption, research in this field is still in its infancy and the data material restricted to only a few fungal species. Thus, the aim of this work was to explore how light influences growth, conidial production and secondary metabolite formation of two industrial relevant strains of M. brunneum (MA 43, formerly M. anisopliae var. anisopliae BIPESCO 5/F52) and B. brongniartii (BIPESCO 2). To achieve this, we constructed an easily adjustable illumination device for highly standardized photophysiological studies of fungi on Petri dishes, the so-called LIGHT BOX. With the aid of this device, M. brunneum and B. brongniartii were grown on S4G or S2G agar at 25 °C for 14 days either in complete darkness or under constant illumination with red light (λpeak = 635 nm), green light (λpeak = 519 nm) or blue light (λpeak = 452 nm). In addition, for each wavelength the effect of different illumination intensities was tested, i.e., intensities of red light ranging from 22.1 ± 0.1 to 136.5 ± 0.3 µW cm-2, green light from 16.5 ± 0.1 to 96.2 ± 0.1 µW cm-2, and blue light from 56.1 ± 0.2 to 188.9 ± 0.6 µW cm-2. Both fungi strongly responded in terms of growth, conidial production, pigmentation and morphology to changes in the wavelength and irradiation intensity. The wavelength-dependent production of the well-known secondary metabolite oosporein which is secreted by the genus Beauveria in particular, was also increased under green and blue light exposure. The established LIGHT BOX system allows not only to optimize conidial production yields with these biotechnologically relevant fungi, but also allows the photobiological exploration of other fungi.

A novel partitivirus orchestrates conidiation, stress response, pathogenicity, and secondary metabolism of the entomopathogenic fungus Metarhizium majus

Mycoviruses are widely present in all major groups of fungi but those in entomopathogenic Metarhizium spp. remain understudied. In this investigation, a novel double-stranded (ds) RNA virus is isolated from Metarhizium majus and named Metarhizium majus partitivirus 1 (MmPV1). The complete genome sequence of MmPV1 comprises two monocistronic dsRNA segments (dsRNA 1 and dsRNA 2), which encode an RNA-dependent RNA polymerase (RdRp) and a capsid protein (CP), respectively. MmPV1 is classified as a new member of the genus Gammapartitivirus in the family Partitiviridae based on phylogenetic analysis. As compared to an MmPV1-free strain, two isogenic MmPV1-infected single-spore isolates were compromised in terms of conidiation, and tolerance to heat shock and UV-B irradiation, while these phenotypes were accompanied by transcriptional suppression of multiple genes involved in conidiation, heat shock response and DNA damage repair. MmPV1 attenuated fungal virulence since infection resulted in reduced conidiation, hydrophobicity, adhesion, and cuticular penetration. Additionally, secondary metabolites were significantly altered by MmPV1 infection, including reduced production of triterpenoids, and metarhizins A and B, and increased production of nitrogen and phosphorus compounds. However, expression of individual MmPV1 proteins in M. majus had no impact on the host phenotype, suggesting insubstantive links between defective phenotypes and a single viral protein. These findings indicate that MmPV1 infection decreases M. majus fitness to its environment and its insect-pathogenic lifestyle and environment through the orchestration of the host conidiation, stress tolerance, pathogenicity, and secondary metabolism.

Positive effects of Cordyceps cateniannulata colonization in tobacco: Growth promotion and resistance to abiotic stress

Background

Entomopathogenic fungi can live in insects to cause disease and death and are the largest group of entomopathogenic microorganisms. Therefore, these fungi are best known for their microbial control potential. Importantly, they also have other beneficial effects, including promoting plant growth and development by colonizing plant. Here, the study sought to identify specific strains of the entomopathogenic fungus, Cordyceps cateniannulata that would form endophytic associations with tobacco, thus benefiting plant growth and resistance to abiotic stresses, thereby highlighting the application of entomopathogenic fungi in tobacco.

Methods

The C. cateniannulata-tobacco symbiont was constructed by root irrigation. The effects of C. cateniannulata on tobacco growth were evaluated by measuring the maximum leaf length, maximum leaf width, number of leaves, plant height, stem thickness, stem circumference, dry and fresh shoot weight 7, 14, 21, and 28 days after colonization. The peroxidase, catalase, superoxide dismutase, and malondialdehyde were measured to observe the impact of C. cateniannulata on tobacco defense enzyme activity. Finally, high-throughput sequencing was used to access microbial communities in the rhizosphere, with data subsequently linked to growth indicators.

Results

After tobacco was inoculated with C. cateniannulata X8, which significantly promoted growth and related enzyme activity, malondialdehyde was decreased. The most significant impact was on peroxidase, with its activity being upregulated by 98.20, 154.42, 180.65, and 170.38% in the four time periods, respectively. The high throughput sequencing results indicated that C. cateniannulata had changed the rhizosphere microbial relative abundances, such as increasing Acidobacteria and Ascomycetes, and decreasing Actinomycetes and Basidiomycetes. The redundancy analysis showed that C. cateniannulata significantly boosted tobacco growth by reducing the abundance of specific dominant genera such as Stachybotrys, Cephalotrichum, Streptomyces, Isoptericola, and Microbacterium.

Conclusion

Specific strains of C. cateniannulata can be introduced into host plants as endophytes, resulting in promotion of host plant growth and increased resistance to abiotic stress and microbial pathogens. The study provides a foundation for future studies of C. cateniannulata as an ecological agent.

The Colonization and Effect of Isaria cateinannulata on Buckwheat Sprouts

The use of entomogenous fungi as endophytes is currently an area of active research. Isaria cateniannulata is an important entomogenous fungus that has been employed for the active control of a range of pests in agricultural and forestry settings, but its direct impact on plants remains to be evaluated. Herein, we assessed the ability of I. cateniannulata to colonize buckwheat, Fagopyrum esculentum and F. tataricum, and its impact on buckwheat defense enzyme activity and physiological indexes. The majority of fungal submerge condia was able to enter into leaves through stomata and veins, and this was followed by conidial attachment, lytic enzyme secretion, conidial deformation, and enhanced defensive enzyme activity within buckwheat, followed by the repair of damaged tissue structures. I. cateniannulata populations on buckwheat leaf surfaces (in CFU/g) reached the minimum values at 24 h after inoculation. At this time, the blast analysis revealed that the sequence identity values were 100%, which was consistent with the sequence of I. cateniannula. The number of I. cateniannulata submerge conidia colonized in the buckwheat leaves gradually rose to peak levels on 7 d post-inoculation, and then gradually declined until 10 d, at which time the buckwheat plant growth index values increased. This study provided novel evidence that I. cateniannulata could be leveraged as an endophytic fungus capable of colonizing buckwheat plants and promoting their growth.

Three Methods Assessing the Association of the Endophytic Entomopathogenic Fungus Metarhizium robertsii with Non-Grafted Grapevine Vitis vinifera

Characterizing the association of endophytic insect pathogenic fungi (EIPF) with plants is an important step in order to understand their ecology before using them in biological control programs. Since several methods are available, it is challenging to identify the most appropriate for such investigations. Here, we used two strains of Metarhizium robertsii: EF3.5(2) native to the French vineyard environment and ARSEF-2575-GFP a laboratory strain expressing a green fluorescent protein, to compare their potential of association with non-grafted grapevine Vitis vinifera. Three methods were used to evaluate the kinetics of rhizosphere and grapevine endospheric colonization: (i) Droplet Digital (ddPCR), a sensitive molecular method of M. robertsii DNA quantification in different plant parts, (ii) culture-based method to detect the live fungal propagules from plant tissues that grew on the medium, (iii) confocal imaging to observe roots segments. Both strains showed evidence of establishment in the rhizosphere of grapevines according to the culture-based and ddPCR methods, with a significantly higher establishment of strain EF3.5(2) (40% positive plants and quantified median of exp(4.61) c/μL) compared to strain ARSEF-2575-GFP (13% positive plants and quantified median of exp(2.25) c/μL) at 96-98 days post-inoculation. A low incidence of association of both strains in the grapevine root endosphere was found with no significant differences between strains and evaluation methods (15% positive plants inoculated with strain EF3.5(2) and 5% with strain ARSEF-2575-GFP according to culture-based method). ddPCR should be used more extensively to investigate the association between plants and EIPF but always accompanied with at least one method such as culture-based method or confocal microscopy.

Organomineral fertilizer application enhances Perilla frutescens nutritional quality and rhizosphere microbial community stability in karst mountain soils

Introduction

Applications of organomineral fertilizer (OMF) are important measures for developing organic agriculture in karst mountain areas. However, the influence of OMF on the structure and function of soil microbial diversity and their relationship with crop yield and quality are still unclear.

Methods

Based on soil science, crop science, and high-throughput sequencing methods, we investigated the changes of rhizosphere soil microbial communities of Perilla frutescens under different fertilization measures. Then, the relationship between P. frutescens yield and quality with soil quality was analyzed.

Results

The results showed that the addition of OMF increased the amount of total carbon and total potassium in soil. OF, especially OMF, improved P. frutescens yield and quality (e.g., panicle number per plant, main panicle length, and unsaturated fatty acid contents). Both OF and OMF treatments significantly increased the enrichment of beneficial microorganism (e.g., Bacillus, Actinomadura, Candidatus_Solibacter, Iamia, Pseudallescheria, and Cladorrhinum). The symbiotic network analysis demonstrated that OMF strengthened the connection among the soil microbial communities, and the community composition became more stable. Redundancy analysis and structural equation modeling showed that the soil pH, available phosphorus, and available potassium were significantly correlated with soil microbial community diversity and P. frutescens yield and quality.

Discussion

Our study confirmed that OMF could replace CF or common OF to improve soil fertility, crop yield and quality in karst mountain soils.