Production of destruxins from Metarhizium spp. fungi in artificial medium and in endophytically colonized cowpea plants

Enzyme regulation patterns in fungal inoculated wheat may reflect resistance and tolerance towards an insect herbivore

Seed inoculation with entomopathogenic fungi (EPF) causes plant-mediated effects against arthropod herbivores, but the responses vary among EPF isolates. We used a wheat model system with three isolates representing Beauveria bassiana and Metarhizium spp. causing either negative or positive effects against the aphid Rhopalosiphum padi. Activities of six carbohydrate enzymes increased in plants showing biomass build-up after EPF inoculations. However, only aldolase activity showed positive correlation with R. padi numbers. Plants inoculated with M. robertsii hosted fewest aphids and showed increased activity of superoxide dismutase, implying a defense strategy of resistance towards herbivores. In M. brunneum-inoculated plants, hosting most R. padi, activities of catalase and glutathione reductase were increased suggesting enhanced detoxification responses towards aphids. However, M. brunneum simultaneously increased plant growth indicating that this isolate may cause the plant to tolerate herbivory. EPF seed inoculants may therefore mediate either tolerance or resistance towards biotic stress in plants in an isolate-dependent manner.

Endophytic entomopathogenic fungi as biological control agents of insect pests

Entomopathogenic fungi capable of establishing mutualistic endophytic relationships with plants have a tremendous potential as biocontrol agents of insect pests. While fungi have long played an important and highly effective role in pest suppression, the utility of endophytic entomopathogenic fungi in pest management is a relatively new and emerging topic of biocontrol. Here we discuss the relevance of endophytic fungi to plant health in general, synthesize the current knowledge of the effectiveness of endophytic entomopathogenic fungi against diverse insect pests, discuss the indirect plant-mediated effects of endophytic entomopathogenic fungi on arthropods, and describe the diverse benefits of endophytic fungi to plants that are likely to affect herbivores and plant pathogens as well. Lastly, we consider major challenges to incorporating endophytic entomopathogenic fungi in biocontrol, such as their non-target effects and field efficacy, which can be variable and influenced by environmental factors. Continued research on endophyte-insect-plant-environment interactions is critical to advancing our knowledge of these fungi as a sustainable pest management tactic. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

A Drosophila melanogaster model shows that fast growing Metarhizium species are the deadliest despite eliciting a strong immune response

We used Drosophila melanogaster to investigate how differences between Metarhizium species in growth rate and mechanisms of pathogenesis influence the outcome of infection. We found that the most rapid germinators and growers in vitro and on fly cuticle were the fastest killers, suggesting that pre-penetration competence is key to Metarhizium success. Virulent strains also induced the largest immune response, which did not depend on profuse growth within hosts as virulent toxin-producing strains only proliferated post-mortem while slow-killing strains that were specialized to other insects grew profusely pre-mortem. Metarhizium strains have apparently evolved resistance to widely distributed defenses such as the defensin Toll product drosomycin, but they were inhibited by Bomanins only found in Drosophila spp. Disrupting a gene (Dif), that mediates Toll immunity has little impact on the lethality of most Metarhizium strains (an exception being the early diverged M. frigidum and another insect pathogen Beauveria bassiana). However, disrupting the sensor of fungal proteases (Persephone) allowed rapid proliferation of strains within hosts (with the exception of M. album), and flies succumbed rapidly. Persephone also mediates gender differences in immune responses that determine whether male or female flies die sooner. We conclude that some strain differences in growth within hosts depend on immune-mediated interactions but intrinsic differences in pathogenic mechanisms are more important. Thus, Drosophila varies greatly in tolerance to different Metarhizium strains, in part because some of them produce toxins. Our results further develop D. melanogaster as a tractable model system for understanding insect-Metarhizium interactions.

Defensive behavior is linked to altered surface chemistry following infection in a termite society

The care-kill response determines whether a sick individual will be treated or eliminated from an insect society, but little is known about the physiological underpinnings of this process. We exploited the stepwise infection dynamics of an entomopathogenic fungus in a termite to explore how care-kill transitions occur, and identify the chemical cues behind these shifts. We found collective responses towards pathogen-injected individuals to vary according to severity and timing of pathogen challenge, with elimination, via cannibalism, occurring sooner in response to a severe active infection. However, injection with inactivated fungal blastospores also resulted in increased albeit delayed cannibalism, even though it did not universally cause host death. This indicates that the decision to eliminate an individual is triggered before pathogen viability or terminal disease status has been established. We then compared the surface chemistry of differently challenged individuals, finding increased amounts of long-chained methyl-branched alkanes with similar branching patterns in individuals injected with both dead and viable fungal blastospores, with the latter showing the largest increase. This coincided with the highest amounts of observed cannibalism as well as signs of severe moribundity. Our study provides new mechanistic insight into the emergent collective behaviors involved in the disease defense of a termite society.

Effects of passages through an insect or a plant on virulence and physiological properties of the fungus Metarhizium robertsii

Species of the genus Metarhizium are characterized by a multitrophic lifestyle of being arthropod parasites, rhizosphere colonizers, endophytes, and saprophytes. The process of adaptation to various organisms and substrates may lead to specific physiological alterations that can be elucidated by passaging through different hosts. Changes in virulence and cultivation properties of entomopathogenic fungi subcultured on different media or passaged through a live insect host are well known. Nevertheless, comparative in-depth physiological studies on fungi after passaging through insect or plant organisms are scarce. Here, virulence, plant colonization, hydrolytic enzymatic activities, toxin production, and antimicrobial action were compared between stable (nondegenerative) parent strain Metarhizium robertsii MB-1 and its reisolates obtained after eight passages through Galleria mellonella larvae or Solanum lycopersicum or after subculturing on the Sabouraud medium. The passaging through the insect caused similar physiological alterations relative to the plant-based passaging: elevation of destruxin A, B, and E production, a decrease in protease and lipase activities, and lowering of virulence toward G. mellonella and Leptinotarsa decemlineata as compared to the parent strain. The reisolates passaged through the insect or plant showed a slight trend toward increased tomato colonization and enhanced antagonistic action on tomato-associated bacterium Bacillus pumilus as compared to the parental strain. Meanwhile, the subculturing of MB-1 on the Sabouraud medium showed stability of the studied parameters, with minimal alterations relative to the parental strain. We propose that the fungal virulence factors are reprioritized during adaptation of M. robertsii to insects, plants, and media.

Investigation on the Influence of Production and Incubation Temperature on the Growth, Virulence, Germination, and Conidial Size of Metarhizium brunneum for Granule Development

Important for the infection of an insect with an entomopathogenic fungus and its use as a plant protection agent are its growth, conidiation, germination, and virulence, which all depend on the environmental temperature. We investigated not only the effect of environmental temperature but also that of production temperature of the fungus. For this purpose, Metarhizium brunneum JKI-BI-1450 was produced and incubated at different temperatures, and the factors mentioned as well as conidial size were determined. The temperature at which the fungus was produced affects its subsequent growth and conidiation on granule formulation, the speed of germination, and the conidial width, but not its final germination or virulence. The growth and conidiation was at its highest when the fungus was produced at 25 °C, whereas when the germination was faster, the warmer the fungus was produced. The incubation temperature optimum of JKI-BI-1450 in relation to growth, speed of germination, and survival time was 25-30 °C and for conidiation 20-25 °C. Conidial length decreased with increasing incubation temperature. Although the fungus could not be adapted to unfavorable conditions by the production temperature, it was found that the quality of a biological control agent based on entomopathogenic fungi can be positively influenced by its production temperature.

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.

Endophytic Metarhizium robertsii suppresses the phytopathogen, Cochliobolus heterostrophus and modulates maize defenses

Fungi in the genus Metarhizium (Hypocreales: Clavicipitaceae) are insect-pathogens and endophytes that can benefit their host plant through growth promotion and protection against stresses. Cochliobolus heterostrophus (Drechsler) Drechsler (Pleosporales: Pleosporaceae) is an economically-significant phytopathogenic fungus that causes Southern Corn Leaf Blight (SCLB) in maize. We conducted greenhouse and lab-based experiments to determine the effects of endophytic M. robertsii J.F. Bisch., Rehner & Humber on growth and defense in maize (Zea mays L.) infected with C. heterostrophus. We inoculated maize seeds with spores of M. robertsii and, at the 3 to 4-leaf stage, the youngest true leaf of M. robertsii-treated and untreated control plants with spores of C. heterostrophus. After 96 h, we measured maize height, above-ground biomass, endophytic colonization by M. robertsii, severity of SCLB, and expression of plant defense genes and phytohormone content. We recovered M. robertsii from 74% of plants grown from treated seed. The severity of SCLB in M. robertsii-treated maize plants was lower than in plants inoculated only with C. heterostrophus. M. robertsii-treated maize inoculated or not inoculated with C. heterostrophus showed greater height and above-ground biomass compared with untreated control plants. Height and above-ground biomass of maize co-inoculated with M. robertsii and C. heterostrophus were not different from M. robertsii-treated maize. M. robertsii modulated the expression of defense genes and the phytohormone content in maize inoculated with C. heterostrophus compared with plants not inoculated with C. heterostrophus and control plants. These results suggest that endophytic M. robertsii can promote maize growth and reduce development of SCLB, possibly by induced systemic resistance mediated by modulation of phytohormones and expression of defense and growth-related genes in maize.

Profiling Destruxin Synthesis by Specialist and Generalist Metarhizium Insect Pathogens during Coculture with Plants

Metarhizium is a genus of endophytic, insect-pathogenic fungi that is used as a biological control agent. The dual lifestyles of these fungi combine the parasitism of insect pests with the symbiotic association with plant roots. A major class of secreted metabolites by Metarhizium are cyclic depsipeptides called destruxins (DTXs). As prominent insecticidal compounds, their role during plant interactions is still largely unknown. Here, we examined the metabolomic profile of Metarhizium, with special emphasis on DTX production, using untargeted, liquid chromatography-tandem mass spectrometry (LC-MS/MS). Four Metarhizium species, two insect generalists (M. robertsii and M. brunneum), and two insect specialists (M. flavoviride and M. acridum) were inoculated onto agar plate cultures containing either bean (Phaseolus vulgaris) or corn (Zea mays) and grown for four and seven days. After methanol extraction, feature-based molecular networking (FBMN) was used to obtain DTX identification as defined by the Global Natural Products Social Molecular Networking (GNPS). A total of 25 DTX analogs were identified, with several DTX-like compounds in coculture that could not be identified. Metarhizium species differed in the amount and type of DTXs they produced, with the insect specialists producing far fewer amounts and types of DTXs than the insect generalists. The production of these metabolites varied between cultures of different ages and plant hosts. Conditions that influence the production of DTXs are discussed. As the genetic arsenal of natural products relates to the lifestyle of the organism, uncovering conditions with an ecological context may reveal strategies for producing novel compounds or precursors suitable for synthetic biology. IMPORTANCE The development of an intimate and beneficial association between fungi and plants requires an exchange of a complex mixture of chemical cues. These compounds are a means of communication, promoting or limiting the interaction, but can have numerous other biological and ecological functions. Determining how the metabolome, or a subset thereof, is linked to plant host preference and colonization has implications for future functional studies and may uncover novel therapeutic compounds whose production is elicited only under cocultivation. In this study, we performed an untargeted metabolomic analysis of plate cocultures with individual plant-fungal pairs. The identification of a major group of fungal metabolites, the destruxins, was examined for their role in plant specificity. The diversity of these metabolites and the production of numerous unidentified, structural analogs are evidence of the sensitivity of the methodology and the potential for future mining of this living data set.

Production of Purpureocillium lilacinum and Pochonia chlamydosporia by Submerged Liquid Fermentation and Bioactivity against Tetranychus urticae and Heterodera glycines through Seed Inoculation

Pochoniachlamydosporia and Purpureocilliumlilacinum are fungal bioagents used for the sustainable management of plant parasitic nematodes. However, their production through submerged liquid fermentation and their use in seed treatment have been underexplored. Therefore, our goal was to assess the effect of different liquid media on the growth of 40 isolates of P. lilacinum and two of P. chlamydosporia. The most promising isolates tested were assessed for plant growth promotion and the control of the two-spotted spider mite (Tetranychus urticae) and the soybean cyst nematode (Heterodera glycines). Most isolates produced > 108 blastospores mL−1 and some isolates produced more than 104 microsclerotia mL−1. Microsclerotia of selected isolates were used to inoculate common bean (Phaseolus vulgaris L.) seeds in greenhouse trials. All fungal isolates reduced the T. urticae fecundity in inoculated plants through seed treatment, while P. chlamydosporia ESALQ5406 and P. lilacinum ESALQ2593 decreased cyst nematode population. Purpureocillium lilacinum was more frequently detected in soil, whereas P. chlamydosporia colonized all plant parts. Pochonia chlamydosporia ESALQ5406 improved the root development of bean plants. These findings demonstrate the possibility of producing submerged propagules of P. chlamydosporia and P. lilacinum by liquid culture, and greenhouse trials support the applicability of fungal microsclerotia in seed treatment to control P. vulgaris pests.

Bioprospecting Trichoderma: A Systematic Roadmap to Screen Genomes and Natural Products for Biocontrol Applications

Natural products derived from microbes are crucial innovations that would help in reaching sustainability development goals worldwide while achieving bioeconomic growth. Trichoderma species are well-studied model fungal organisms used for their biocontrol properties with great potential to alleviate the use of agrochemicals in agriculture. However, identifying and characterizing effective natural products in novel species or strains as biological control products remains a meticulous process with many known challenges to be navigated. Integration of recent advancements in various "omics" technologies, next generation biodesign, machine learning, and artificial intelligence approaches could greatly advance bioprospecting goals. Herein, we propose a roadmap for assessing the potential impact of already known or newly discovered Trichoderma species for biocontrol applications. By screening publicly available Trichoderma genome sequences, we first highlight the prevalence of putative biosynthetic gene clusters and antimicrobial peptides among genomes as an initial step toward predicting which organisms could increase the diversity of natural products. Next, we discuss high-throughput methods for screening organisms to discover and characterize natural products and how these findings impact both fundamental and applied research fields.

Insect-fungal-interactions: A detailed review on entomopathogenic fungi pathogenicity to combat insect pests

Global food security is threatened by insect pests of economically important crops. Chemical pesticides have been used frequently for the last few decades to manage insect pests throughout the world. However, these chemicals are hazardous for human health as well as the ecosystem. In addition, several pests have evolved resistance to many chemicals. Finding environment friendly alternatives lead the researchers to introduce biocontrol agents such as entomopathogenic fungi (EPF). These fungi include various genera that can infect and kill insects efficiently. Moreover, EPFs have considerable host specificity with a mild effect on non-target organisms and can be produced in bulk quantity quickly. However, insights into the biology of EPF and mechanism of action are of prime significance for their efficient utilization as a biocontrol agent. This review focuses on EPF-mediated insect management by explaining particular EPF strains and their general mode of action. We have comprehensively discussed which criteria should be used for the selection of pertinent EPF, and which aspects can impact the EPF efficiency. Finally, we have outlined various advantages of EPF and their limitations. The article summarizes the prospects related to EPF utilization as biocontrol agents. We hope that future strategies for the management of insects will be safer for our planet.

Observations on the Relationships between Endophytic Metarhizium robertsii, Spodoptera frugiperda (Lepidoptera: Noctuidae), and Maize

Fungi in the genus Metarhizium are entomopathogens that can establish endophytically inside plants and benefit them through growth promotion and pest suppression. Lab- and greenhouse-based experiments were conducted to examine the effects of endophytic M. robertsii colonization in maize (Zea mays) on fall armyworm (FAW) (Spodoptera frugiperda). Maize seeds were inoculated with M. robertsii conidia, plants were evaluated for endophytic colonization, and then relative growth rate (RGR) and feeding behavior of larval FAW fed leaves from inoculated and uninoculated maize were measured. Endophytic M. robertsii was recovered from 60.5% of inoculated maize. In feeding bioassays, the RGR of larval FAW fed leaves of inoculated maize was no different than the RGR of larvae fed leaves from uninoculated maize. The RGR of larval FAW was positively correlated with the proportion of endophytic colonization of maize leaf and root tissues; however, in feeding assays, FAW larvae demonstrated no preference for consuming leaf tissue from inoculated or uninoculated maize. The proportion of leaf tissue consumed was unrelated to the proportion of M. robertsii-colonization of leaf or root tissue from source plants. We discuss possible reasons why FAW were not affected by endophytic M. robertsii in the context of assay methodology, FAW physiology, and induced maize defenses.

Seed inoculations with entomopathogenic fungi affect aphid populations coinciding with modulation of plant secondary metabolite profiles across plant families

Entomopathogenic fungi (EPF) can display a plant-associated lifestyle as endophytes. Seed application of EPF can affect insect herbivory above ground, but the mechanisms behind this are not documented. Here we applied three EPF isolates, Beauveria bassiana, Metarhizium brunneum and M. robertsii, as seed inoculation of wheat and bean, and evaluated the effects on population growth of aphids, Rhopalosiphum padi and Aphis fabae, respectively. In wheat and bean leaves, we quantified benzoxazinoids and flavonoids, respectively, in response to EPF inoculation and aphid infestation to elucidate the role of specific plant secondary metabolites (PSMs) in plant-fungus-herbivore interactions. Inoculations of wheat and bean with M. robertsii and B. bassiana reduced aphid populations compared with control treatments, whereas M. brunneum unexpectedly increased the populations of both aphids. Concentrations of the majority of PSMs were differentially altered in EPF-treated plants infested with aphids. Changes in aphid numbers were associated with PSMs regulation rather than EPF endophytic colonisation capacity. This study links the effects of EPF seed inoculations against aphids with unique PSM accumulation patterns in planta. The understanding of PSM regulation in tri-trophic interactions is important for the future development of EPF for pest management.

Direct and Indirect Effect via Endophytism of Entomopathogenic Fungi on the Fitness of Myzus persicae and Its Ability to Spread PLRV on Tobacco

Simple Summary

Aphids are major crop pests that are feeding on plant sap and transmitting plant viruses, thus inducing high yield losses worldwide. As chemical pesticides are decreasingly used in plant protection, fungi that cause disease to insects (entomopathogenic fungi) are one of the promising alternatives. They are commonly applied by spraying plants to protect them against herbivores. When applied, some fungi penetrate and live within plant tissues, thus helping to internally protect from insect attacks and other plant diseases. The aim of our study was to assess the effects of entomopathogenic fungi (EPF) applied firstly by contact after insect direct spraying, secondly by endophytic plant inoculation, and thirdly by associated both methods assessing the green peach aphid performances. The impact of the presence of endophytic entomopathogenic fungi (EEPF) in plant tissues on virus transmission by aphids was also considered. We found that the EPF Beauveria bassiana killed the green peach aphid and reduced its fecundity regardless of the application method. On fungal-inoculated plants, there was also a high mortality of aphid nymphs and infection by the potato leafroll virus (PLRV) was delayed by about a week with the EEPF treatment compared to fungal-free plants. This study showed that spraying plant leaves with EPF not only has a direct insecticidal effect against insects but could also have beneficial side effects for the plant against viruses.

Abstract

Aphids are major crop pests that transmit more than half of all insect-vectored plant viruses responsible for high yield losses worldwide. Entomopathogenic fungi (EPF) are biological control agents mainly used by foliar application to control herbivores, including sap-sucking pests such as aphids. Their ability to colonize plant tissues and to interact with diverse plant pathogenic microorganisms have been reported. In our study, we evaluated the effectiveness of Beauveria bassiana ((Balsamo-Crivelli) Vuillemin) directly applied by contact or/and indirectly via endophytism in tobacco plants (Nicotiana tabacum L.) against the virus vector Myzus persicae (Sulzer) carrying the Potato leafroll virus (PLRV) or not. We found that both contact treatment and endophytic colonization of leaves significantly increased aphid mortality and decreased the fecundity rate when compared to control plants. In addition, on fungal-colonized leaves, viruliferous aphids were more negatively impacted than virus-free ones and nymph mortality was significantly higher than on fungal-free plants. Furthermore, we assessed PLRV transmission by M. persicae on tobacco plants inoculated with either B. bassiana or Metarhizium acridum ((Driver and Milner) JF Bischoff, Rehner, and Humber) as source or/and recipient plants. Myzus persicae was found to acquire and transmit PLRV regardless of the treatment. Nevertheless, the infection rate of endophytically colonized plants was lower at a seven-day incubation period and had increased to almost 100% after fifteen days. These results suggest that B. bassiana is effective against aphids, both by contact and via endophytism, and both B. bassiana and M. acridum delayed PLRV infection in tobacco.

Endophytic fungi protect tomato and nightshade plants against Tuta absoluta (Lepidoptera: Gelechiidae) through a hidden friendship and cryptic battle

Endophytic fungi live within plant tissues without causing any harm to the host, promote its growth, and induce systemic resistance against pests and diseases. To mitigate the challenging concealed feeding behavior of immature stages of Tuta absoluta in both tomato (Solanum lycopersicum) and nightshade (Solanum scabrum) host plants, 15 fungal isolates were assessed for their endophytic and insecticidal properties. Twelve isolates were endophytic to both host plants with varied colonization rates. Host plants endophytically-colonized by Trichoderma asperellum M2RT4, Beauveria bassiana ICIPE 706 and Hypocrea lixii F3ST1 outperformed all the other isolates in reducing significantly the number of eggs laid, mines developed, pupae formed and adults emerged. Furthermore, the survival of exposed adults and F1 progeny was significantly reduced by Trichoderma sp. F2L41 and B. bassiana isolates ICIPE 35(4) and ICIPE 35(15) compared to other isolates. The results indicate that T. asperellum M2RT4, B. bassiana ICIPE 706 and H. lixii F3ST1 have high potential to be developed as endophytic-fungal-based biopesticide for the management of T. absoluta.

Systemic Colonization by Metarhizium robertsii Enhances Cover Crop Growth

Fungi in the genus Metarhizium (Hypocreales: Clavicipitaceae) are insect pathogens that can establish as endophytes and can benefit their host plant. In field experiments, we observed a positive correlation between the prevalence of M. robertsii and legume cover crops, and a negative relationship with brassicaceous cover crops and with increasing proportion of cereal rye in mixtures. Here, we report the effects of endophytic M. robertsii on three cover crop species under greenhouse conditions. We inoculated seeds of Austrian winter pea (Pisum sativum L., AWP), cereal rye (Secale cereale L.), and winter canola (Brassica napus L.) with conidia of M. robertsii to assess the effects of endophytic colonization on cover crop growth. We recovered M. robertsii from 59%, 46%, and 39% of seed-inoculated AWP, cereal rye, and canola plants, respectively. Endophytic M. robertsii significantly increased height and above-ground biomass of AWP and cereal rye but did not affect chlorophyll content of any of the cover crop species. Among inoculated plants from which we recovered M. robertsii, above-ground biomass of AWP was positively correlated with the proportion of colonized root but not leaf tissue sections. Our results suggest that winter cover crops may help to conserve Metarhizium spp. in annual cropping systems.

Microsclerotia production of Metarhizium spp. for dual role as plant biostimulant and control of Spodoptera frugiperda through corn seed coating

The fungal genus Metarhizium comprises entomopathogenic species capable of producing overwintering structures known as microsclerotia. These structures offer many advantages in pest control due to the formation of infective conidia in situ and their persistence in the environment under adverse conditions. In addition, the in vitro production of Metarhizium microsclerotia under controlled liquid fermentation is faster and with greater process control than the production of aerial conidia. However, the potential of Metarhizium microsclerotia to control pests from the orders Lepidoptera and Hemiptera is unexplored. In this study, we examined the ability of Metarhizium spp. microsclerotia to promote corn growth and to provide plant protection against Spodoptera frugiperda (Lepidoptera: Noctuidae) and Dalbulus maidis (Hemiptera: Cicadellidae), through seed coating using microsclerotial granules. A screening to find higher microsclerotia producers was conducted by culturing 48 native Brazilian isolates of Metarhizium spp. (Metarhizium anisopliae, Metarhizium robertsii, Metarhizium humberi and Metarhizium sp. indeterminate). The best microsclerotia producers, M. anisopliae ESALQ1814, M. robertsii ESALQ2450 and M. humberi ESALQ1638 improved the leaf area, plant height, root length, and dry weight of plants compared to un-inoculated plants. Significant reduction in S. frugiperda survival (mortality > 55% after 7 days) was observed when larvae were fed on corn plants treated with any of the three Metarhizium species. Conversely, survival of D. maidis adults were unaffected by feeding on fungus-inoculated plants. Our results suggest that microsclerotia of Metarhizium spp. may act as biostimulants and to provide protection against S. frugiperda in corn through seed coating, thus adding an innovative strategy into the integrated management of this major worldwide pest.

Endophytic Entomopathogenic Fungi: A Valuable Biological Control Tool against Plant Pests

Among the non-chemical insect control methods, biological control is one of the most effective human and environmentally friendly alternatives. One of the main biological control methods is the application of entomopathogenic fungi (EPF). Today, biological crop protection with EPF plays a key role in projects for the sustainable management of insect pests. EPF have several advantages over conventional insecticides, including cost-effectiveness, high yield, absence of harmful side-effects for beneficial organisms, fewer chemical residues in the environment and increased biodiversity in ecosystems. Apart from direct application as contact bioinsecticides, EPF are able to colonize plants as endophytes acting not only as pest and disease control agents but also as plant growth promoters. The present paper presents an outline of the biocontrol potential of several EPF, which could be harnessed for the development of new integrated pest Management (IPM) strategies. Emphasis is given on benefits of endophytic EPF, on issues for practical application and in fields in need of further research. Our findings are discussed in the context of highlighting the value of entomopathogenic fungal endophytes as an integral part of pest management programs for the optimization of crop production.

Advanced strategy to produce insecticidal destruxins from lignocellulosic biomass Miscanthus

BACKGROUND

Biorefineries are widely recognized as the most feasible solution to the problem of achieving environmental sustainability along with economic growth. Furthermore, pine wilt disease has caused severe environmental and economic damage worldwide to date. Herein, a highly efficient, advanced process for producing destruxins (DTXs) from Miscanthus (MCT) is reported, along with an application strategy.

RESULTS

The acetic acid-sodium chlorite pretreatment of MCT (AASC-MCT) is found to improve the monosaccharide production. Through biocatalytic conversion processes (simultaneous saccharification and cultivation), Metarhizium anisopliae JEF-279 can efficiently produce DTXs from 1% (w/v) AASC-MCT, i.e., DTX E (334.8 mg/L), A (288.8 mg/L), and B (48.6 mg/L). Monochamus alternatus (MA, Japanese pine sawyer) is known to act as a mediator transferring Bursaphelenchus xylophilus to pinewood. As B. xylophilus is associated with the occurrence of pine wilt disease, biological control of MA is a major strategy or controlling this disease. In this study, upon the application of a mixture of DTXs and protease-containing culture filtrate (PCF), complete mortality of MA is observed after a 5-day incubation. The MA immune system response is believed to cause an overexpression of actin and tropomyosin as a defense mechanism against the flaccid paralysis induced by the DTXs and PCF treatment.

CONCLUSIONS

These results suggest that MCT can be used as a major feedstock in the biorefinery industry and that DTXs can be applied as an insecticide for biological control of pine wilt disease via MA termination.

Transcriptional Reprogramming of Arabidopsis thaliana Defence Pathways by the Entomopathogen Beauveria bassiana Correlates With Resistance Against a Fungal Pathogen but Not Against Insects

The entomopathogenic fungus Beauveria bassiana can adopt an endophytic lifestyle by colonising a wide array of plant species. Beauveria-colonised plants can show enhanced resistance against insects and plant pathogens alike. However, little is known about the molecular and physiological mechanisms that govern such interactions. Here, we assessed the effects of two B. bassiana strains (BG11, FRh2) on the growth of Arabidopsis thaliana and its resistance against two herbivore species and a phytopathogen. Plant responses were studied on the transcriptomic and metabolic level using microarrays and by measuring changes in defence-related phytohormones and glucosinolates (GLSs). Root inoculation with B. bassiana BG11 significantly increased plant growth, while FRh2 had no such effect. Both Beauveria strains decreased leaf lesion area caused by the phytopathogen Sclerotinia sclerotiorum but did not affect population growth of the aphid Myzus persicae or the growth of Plutella xylostella caterpillars. Microarray analyses of leaves from endophyte-inoculated A. thaliana provided evidence for transcriptional reprogramming of plant defence pathways, with strain-specific changes in the expression of genes related to pathogenesis, phytoalexin, jasmonic (JA), and salicylic acid (SA) signalling pathways. However, B. bassiana colonisation did not result in higher concentrations of JA and SA or major changes in leaf GLS profiles. We conclude that the endophyte B. bassiana induces plant defence responses and hypothesise that these contribute to enhanced resistance against S. sclerotiorum.

Seed inoculation with endophytic fungal entomopathogens promotes plant growth and reduces crown and root rot (CRR) caused by Fusarium culmorum in wheat

Fungal entomopathogens, Beauveria bassiana (NATURALIS) and Metarhizium brunneum (BIPESCO5), can promote the growth of wheat following their endophytic establishment within plants through seed treatment. Similar to endophytic B. bassiana which has already been reported as a disease antagonist by several previous studies, the present study demonstrates that M. brunneum can suppress disease pathogens following plant colonization as well. An upsurge of research hints at the ability of entomopathogenic fungi, almost exclusively considered and used as insect pathogens, to endophytically colonize the internal tissues of a wide array of host plants and subsequently confer numerous benefits including enhancement of plant growth and suppression of disease pathogens. Such an ability has mainly been investigated for Beauveria bassiana. Fewer studies have demonstrated plant growth promotion by Metarhizium brunneum colonization, whereas no studies have reported on the potential of endophytic M. brunneum as a plant disease antagonist. The present study was, therefore, conducted to investigate whether seed treatment with B. bassiana (NATURALIS) and M. brunneum (BIPESCO5) could result in their endophytic establishment in wheat and promote plant growth. The study further examines the effect of the fungal strains as endophytes against Fusarium culmorum, one of the main causal agents of crown and root rot (CRR) in wheat. Both B. bassiana and M. brunneum were able to systemically colonize roots and shoots of wheat, and promote several plant growth parameters (shoot height, root length, and fresh root and shoot weights). Moreover, endophytic colonization of wheat with either fungal entomopathogen resulted in a significant reduction in disease incidence, development and severity. These results support the notion of the multiple ecological roles that could further be played by entomopathogenic fungi. Bearing such additional roles in mind while developing these fungi as microbial agents could improve the value of many commercially available mycoinsecticides.

Initial stages of endophytic colonization by Metarhizium involves rhizoplane colonization

Here we assessed the time course of rhizoplane colonization by the endophytic insect pathogenic fungus Metarhizium robertsii. We describe a method of quantifying root colonization of bean plants by M. robertsii using quantitative polymerase chain reaction (qPCR). Results of this method were compared to the standard plate count method using colony-forming units (c.f.u.). Both the c.f.u. and qPCR methods were used to monitor the time-course of haricot bean (Phaseolus vulgaris) colonization by a strain of M. robertsii that expresses the green fluorescent protein (ARSEF 2575-GFP) for colony verification. There was a strong correlation between the results of the c.f.u. and qPCR methods, indicating that both methods are well suited for the determination of colonization of P. vulgaris roots by M. robertsii. Primers for a catalase gene (cat) amplified DNA from M. robertsii, M. brunneum and M. guizhouense. Primers for a nitrogen response-regulator (nrr) additionally detected M. acridum and M. flavoviride, whereas Metarhizium perilipin-like protein (mpl) primers were specific to M. robertsii alone. However, cat was the only target that specifically amplified Metarhizium in experiments utilizing non-sterile soil. Endophytic colonization of P. vulgaris at 60 days post-inoculation with M. robertsii was detected from surface-sterilized roots with more sensitivity using our qPCR technique over the c.f.u. method. Our results suggest that there is a prolonged period of rhizoplane colonization by Metarhizium with transient, low-level endophytic colonization of the root system of P. vulgaris that persists for the entirety of the plant life cycle.

Prospects of endophytic fungal entomopathogens as biocontrol and plant growth promoting agents: An insight on how artificial inoculation methods affect endophytic colonization of host plants

Entomopathogenic fungi (EPF) can be established as endophytes in the host plants to offer a long-term preventive measure for pests and diseases. This practice serves as a better alternative to the common practice of periodic direct application of EPF on plants or the target pests as a short-term defense strategy against pests and diseases. These fungal endophytes, aside from their role in pests and diseases prevention, also act as plant growth promoters. Several fungal endophytes have been associated with improvement in plant height, dry and wet weight and other growth parameters. However, many limiting factors have been identified as mitigating the successful colonization of the host plants by EPF. The inoculation methods used have been identified as one, but sadly, this has received little or less attention. Some previous studies carried out comparison between various artificial inoculation methods; foliar application, seedling dipping, soil drenching, seed inoculation, direct injection and others. In separate studies, some authors had suggested different application methods that are best suitable for certain fungal entomopathogens. For instance, leaf inoculation with conidial suspensions was suggested to be the best inoculation method for Beauveria bassiana in sorghum, stem injection was suggested as the most suitable for coffee, while, root dipping method proved the most successful for B. bassiana colonization of tomato plants for the management of Helicoverpa armigera. Here, we discussed entomopathogenic fungal endophytes as bio-control agents, plant growth promoters and highlighted the effect of various artificial inoculation methods on their endophytic colonization of the host plants.

Quantification of fungal growth and destruxin A during infection of Galleria mellonella larvae by Metarhizium brunneum

Destruxin A is among the major secondary metabolites produced by the entomopathogenic ascomycete Metarhizium sp., and the lack of studies concerning production of destruxin A by the fungus is most likely the biggest obstacle for the registration of new fungal strains. Although several studies focus on the production of destruxin A in culture media, few studies examine destruxin A in vivo during host infection. In the current work, Galleria mellonella was used as an insect model to develop for the first time in vivo real-time PCR- and HPLC-MS-based quantification of fungal growth and metabolite production, respectively, during infection by two strains of M. brunneum. Total mortality of sixth instar G. mellonella larvae that were immersed in a suspension of 1.0×10⁸conidiamL^-1 of M. brunneum EAMa 01/58-Su or BIPESCO5 strains reached 85.5% and 78.8%, respectively, and the percentage of cadavers with fungal outgrowth was low at 12.2% and 4.4%, respectively. The average survival time of treated larvae was 5.5days for both fungal strains. Using EAMa 01/58-Su and BIPESCO5 specific primer set, real-time PCR showed that the patterns of fungal growth were different for the two strains, whereas no significant differences were detected in the number of fungal sequence copies recovered from the infected larvae. EAMa 01/58-Su and BIPESCO5 strains secreted destruxin A from days 2 to 6 and from days 2 to 5 post treatment, respectively. For EAMa 01/58-Su and BIPESCO5, the maximum titer of destruxin A in the host was on day 4 at 0.369 and 0.06µg/larva, respectively, and throughout the pathogenic process, the total production was 0.6 and 0.09µg/larva, respectively. These results demonstrated that the strains pose a low hazard, if any, to humans and the environment. The methods used in this study to quantify fungal growth and metabolite production provided valuable data to better understand the role of destruxin A during the growth of M. brunneum in the host larvae and to monitor the fate of destruxin A in food chains.