Nomuraea Rileyi Research Articles

Mrlac1, an extracellular laccase, is required for conidial morphogenesis as well as the well adaptability in field of Metarhizium rileyi

Acting as an extremely promising fungal pesticide, Metarhizium rileyi exhibits robust insecticidal activity against Lepidoptera pests, particularly the larvae. Though there is a slight delay in efficacy, biopesticides offer salient advantages over traditional chemical pesticide especially in environmental safety, cyclic infection and resistant inhibition. In this study, an exterior T-DNA was randomly inserted into the genome of M. rileyi, resulting in the acquisition of a mutant strain that displayed a colour transition from green to yellow within its conidia. The disruption of Mrlac1, a laccase, has been confirmed to attribute to the epigenetic alterations. Mrlac1 is a secreted protein harboring an N-terminal signaling peptide that undergoes in vivo synthesis and accumulates on the cell wall of M. rileyi. Targeted knock-out mutant exhibited alterations not just in conidia coloration, but significantly diminished capacity to withstand external stressors, particularly non-biological factors such as high humidity, Congo red exposure, and UV radiation. The disruptant suffered a constraint on hyphal polar growth, alteration in conidial surface structure, as well as noticeable increase in adhesion forces between conidia, the core infection factors. There is a remarkable diminution in virulence of Mrlac1 deletion variant against larvae of Spodoptera litura by topical inoculation, but not hemolymph injection. Our findings suggest that Mrlac1 acts as a positive regulator in the normal morphogenesis of fungal conidia, encompassing pigment production, inter-conidia adhesion, and conidial cell wall integrity, while the preservation of these structures holds paramount importance for the survival and infection of M. rileyi in the field.

Molecular Characterization of Native Isolates of Metarhizium rileyi (Farlow) Samson (Ascomycetes: Hypocreales) from Major Cropping Ecosystems of Northeastern Karnataka, India

Aims: In India, commercial biopesticides have been recommended against different insect pests on different crops, but their application has shown only a reduced efficiency attributed to differences in susceptibility of target insect pests or non-adaptability to Indian agro-climatic conditions. Therefore, there is a need to isolate region-specific biopesticide strains to enhance the efficacy of such biopesticides for pest management. The current study aimed to explore the new isolates of the entomopathogenic fungus, Metarhizium rileyi (Farlow) Samson species across the major cropping ecosystems of kalyana Karnataka. M. rileyi is an important entomopathogenic fungus of more than 30 species of Lepidoptera larvae. The aim of this research was to characterize the isolate of M. rileyi from Northeastern Karnataka by using morphological and molecular approaches. Methodology: The fungus was isolated from the naturally infected cadavers collected from different cropping ecosystems and it was cultured on Sabouraud’s Maltose Yeast Extract Agar (SMAY) media for morphological characterization, SMY media used for molecular characterization. The vegetative hyphae of fungi were 2-3 µm in diameter and hyaline, septate. The conidia ellipsoidal, smooth, and pale green were observed under the optical microscope. The DNA was isolated using the CTAB method and an internal transcribed spacer (ITS1, ITS4) was used as the primers for the amplification. The amplified products of 650 bp were purified and sequenced at ClustaL W in both directions using the above primers. A consensus sequence was obtained by alignment of the forward and reverse sequences for this region and deposited in GenBank (UASRBC Mr-24, UASRBC Mr-3, UASRBC Mr-20, UASRBC Mr-29, UASRBC Mr-7, UASRBC Mr-18). Result: A BLAST search of the sequence in GenBank revealed a 50-100 percent identity with several strains of M. rileyi (Eg. JQ686668, MN907775 and KJ725726 etc.,). Conclusion: The phylogenetic relationship was derived from comparisons of the ITS gene sequences and a Dendrogram was constructed. The homology and variations based on amino acid sequences among the isolates showed 71 per cent (OK184897) and 51 per cent similarity with four isolates (OK184899, OK177835, OK178862 and OK184898).

Pathogenicity of native strains of Bacillus thuringiensis, Beauveria bassiana and Metarhizium rileyi as entomopathogens against the polyphagous borer, Conogethes punctiferalis (Guenée) (Crambidae: Lepidoptera)

BackgroundThe shoot and fruit borer, Conogethes punctiferalis (Guenée) (Crambidae: Lepidoptera), is a significant pest causing substantial economic losses across various crops. The need for alternative control methods has prompted the exploration of biological control using entomopathogenic fungi and bacteria. In this study, the pathogenicity of Beauveria bassiana, Metarhizium (Nomuraea) rileyi and Bacillus thuringiensis (Bt) against C. punctiferalis larvae and pupae was assessed through laboratory bioassays.ResultsVarious concentrations of B. bassiana and M. rileyi spores, i.e. 1 × 102, 1 × 104, 1 × 106, 1 × 107 and 1 × 108 spores/ml, were tested alongside controls. Additionally, five strains of Bt (IIOR Bt-145, Bt-154, Bt-171, Bt-172 and Bt-127) were evaluated at concentrations of 0.5, 1.0, 1.5, 2.0 and 2.5 mg/ml. The LC50 values for B. bassiana and M. rileyi were 7.9 × 105 spores/ml and 8.7 × 104 spores/ml, respectively, after 4 and 6 days of post-treatment using the spray method. In the larval dip method, the LC50 values were 4.8 × 103 spores/ml for B. bassiana and 2.0 × 104 spores/ml for M. rileyi after 5 and 6 days of treatment, respectively. For pupae, the LC50 values were 1.2 × 106 spores/ml for B. bassiana and 4.3 × 104 spores/ml for M. rileyi after 4 and 7 days of treatment, respectively. Similarly, the five strains of Bt were effective against C. punctiferalis. However, Bt-154 demonstrated the highest efficacy, with LC50 values of 0.66 mg/ml in the spray method and 0.79 mg/ml in the larval dip method after 5 days of post-treatment.ConclusionThe potential of entomopathogenic isolates as biocontrol agents against C. punctiferalis provided a promising alternative to synthetic insecticides in pest management. The efficacy of B. bassiana, M. rileyi and Bt strains suggests their suitability for integrated pest management strategies, potentially reducing reliance on chemical pesticides and minimizing the environmental impacts. Further field studies are warranted to validate the efficacy and practicality of these biocontrol agents in real-world agricultural settings.

The Catalase Gene MrCat1 Contributes to Oxidative Stress Tolerance, Microsclerotia Formation, and Virulence in the Entomopathogenic Fungus Metarhizium rileyi.

Catalases play a crucial role in the metabolism of reactive oxygen species (ROS) by converting H2O2 into molecular oxygen and water. They also contribute to virulence and fungal responses to various stresses. Previously, the MrCat1-deletion mutant (ΔMrCat1) was generated using the split-marker method in Metarhizium rileyi. In this study, the Cat1 gene was identified, and its function was evaluated. Under normal culture conditions, there were no significant differences in colony growth or dimorphic switching between ΔMrCat1 and the wild-type (WT) strains. However, under oxidative stress, the colony growth was inhibited, and the yeast-hyphal transition was suppressed in the ΔMrCat1 strain. Hyperosmotic stress did not differ significantly between the two strains. In the ΔMrCat1 strain, microsclerotia (MS) formation was delayed, resulting in less uniform MS size and a 76% decrease in MS yield compared to the WT strain. Moreover, the ΔMrCat1 strain exhibited diminished virulence. Gene expression analysis revealed up-regulation of ΔMrCat1, MrCat2, MrCat4, and MrAox in the ΔMrCat1 strain. These findings indicate that the MrCat1 gene in M. rileyi is essential for oxidative stress tolerance, MS formation, and virulence.

Oleic Acid and Linoleic Acid Enhances the Biocontrol Potential of Metarhizium rileyi.

Metarhizium rileyi is a wide spread insect fungi with a good biocontrol potentiality to various pests, particularly noctuid insects. However, it is characterized by its slow growth, its sensitivity to abiotic stress, and the slow speed of kill to pests, which hinder its use compared with other entomopathogenic fungi. In this study, the responses of M. rileyi to eight types of lipids were observed; among the lipids, oleic acid and linoleic acid significantly promoted the growth and development of M. rileyi and enhanced its stress tolerances and virulence. An additional mechanistic study demonstrated that exogenous oleic acid and linoleic acid significantly improved the conidial germination, appressorium formation, cuticle degradation, and cuticle infection, which appear to be largely dependent on the up-regulation of gene expression in growth, development, protective, and cuticle-degrading enzymes. In conclusion, exogenous oleic acid and linoleic acid enhanced the stress tolerances and virulence of M. rileyi via protecting conidial germination and promoting cuticle infection. These results provide new insights for the biopesticide development of M. rileyi.

Dusting Metarhizium rileyi conidia with a drone for controlling fall armyworm and soybean looper in maize and soybean fields

Dusting Metarhizium rileyi conidia with a drone for controlling fall armyworm and soybean looper in maize and soybean fields

Natural Prevalence, Molecular Characteristics, and Biological Activity of Metarhizium rileyi (Farlow) Isolated from Spodoptera frugiperda (J. E. Smith) Larvae in Mexico.

Entomopathogenic fungi have been considered potential biological control agents against the fall armyworm Spodoptera frugiperda (J. E. Smith), the world's most important pest of maize. In this study, we evaluated the natural infection, molecular characteristics, and biological activity of Metarhizium rileyi (Farlow) isolated from S. frugiperda larvae of this insect, collected from maize crops in five Mexican locations. Natural infection ranged from 23% to 90% across all locations analyzed. Twenty-four isolates were evaluated on S. frugiperda second instars at a concentration of 1.0 × 108 conidia/mL, causing 70% to 98.7% mortality and 60.5% to 98.7% sporulation. Isolates T9-21, Z30-21, PP48-21, and L8-22 were selected to determine their phylogenetic relationships by β-tubulin gene analysis and to compare median lethal concentration (CL50), median lethal time (LT50), and larval survival. These isolates were grouped into three clades. The T9-21, PP48-21, and J10-22 isolates were closely related (clade A), but phylogenetically distant from Z30-21 (clade B) and L8-22 (clade C) isolates. These genetic differences were not always reflected in their pathogenicity characteristics since no differences were observed among the LC50 values. Furthermore, isolates T9-21, J10-22, and L8-22 were the fastest to kill S. frugiperda larvae, causing lower survival rates. We conclude that native M. rileyi isolates represent an important alternative for the biocontrol of S. frugiperda.

Gut Microbial Diversity Reveals Differences in Pathogenicity between Metarhizium rileyi and Beauveria bassiana during the Early Stage of Infection in Spodoptera litura Larvae.

Beauveria bassiana and Metarhizium rileyi are extensively utilized to investigate fungal pathogenic mechanisms and to develop biological control agents. Notwithstanding, notable distinctions exist in their pathogenicity against the same host insect. This study aimed to elucidate the pathogenic differences between M. rileyi and B. bassiana by examining the impact of various ratios of B. bassiana strain AJS91881 and M. rileyi strain SXBN200920 on fifth instar larvae of Spodoptera litura, focusing on early infection stages and intestinal microbial community structure. The lethal time 50 (LT50) for B. bassiana was significantly lower than that for M. rileyi, indicating greater efficacy. Survival analyses in mixed groups (ratios of 1:9, 1:1, and 9:1 M. rileyi to B. bassiana) consistently demonstrated higher virulence of B. bassiana. Intestinal microbial diversity analysis revealed a significant increase in Achromobacter and Pseudomonas in larvae infected with M. rileyi, whereas Weissella was notably higher in those infected with B. bassiana. Additionally, significant shifts in microbial genera abundances were observed across all mixed infection groups. KEGG pathway enrichment analysis indicated that M. rileyi and B. bassiana employ distinct pathogenic strategies during early infection stages. In vitro tests confirmed the superior growth and stress resistance of B. bassiana compared to M. rileyi, but the antifungal ability of M. rileyi was better than that of B. bassiana. In conclusion, our findings provide preliminary insights into the differential pathogenic behaviors of M. rileyi and B. bassiana during the early infection stages in S. litura larvae, enhancing our understanding of their mechanisms and informing biological pest control strategies in agriculture and forestry.

Management of Fall Armyworm (Spodoptera frugiperda) in Maize with Oil Based Formulations of Metarhizium rileyi

Maize, a vital cereal crop globally and in India, faces productivity challenges exacerbated by invasive pests like the fall armyworm. In response, eco-friendly strategies like microbial-based pesticides, including Metarhizium rileyi, is emerging as promising solution. This study addresses the challenge for effective fall armyworm management by utilizing M. rileyi oil based formulations. Results demonstrate significant larval reduction, with sunflower oil-based formulations achieving the highest reduction of 49.12% compared to control. These findings underscore the potential of M. rileyi formulations, particularly in sunflower oil, as valuable tools in integrated pest management strategies for maize crops.

Novel report on soil infection with Metarhizium rileyi against soil-dwelling life stages of insect pests.

Entomopathogenic fungi are the most effective control remedy against a wide range of medical and agricultural important pests. The present study aimed to isolate, identify, and assess the virulence of Metarhizium rileyi against Spodoptera litura and Spodoptera frugiperda pupae under soil conditions. The biotechnological methods were used to identify the isolate as M. rileyi. The fungal conidial pathogenicity (2.0 × 107, 2.0 × 108, 2.0 × 109, 2.0 × 1010, and 2.0 × 1011 conidia/mL-1) was tested against prepupae of S. litura and S. frugiperda at 3, 6, 9, and 12 days after treatments. Additionally, the artificial soil-conidial assay was performed on a nontarget species earthworm Eudrilus eugeniae, using M. rileyi conidia. The present results showed that the M. rileyi caused significant mortality rates in S. litura pupae (61-90%), and S. litura pupae were more susceptible than S. frugiperda pupae (46%-73%) at 12 day posttreatment. The LC50 and LC90 of M. rileyi against S. litura, were 3.4 × 1014-9.9 × 1017 conidia/mL-1 and 6.6 × 105-4.6 × 1014 conidia/mL-1 in S. frugiperda, respectively. The conidia of M. rileyi did not exhibit any sublethal effect on the adult stage of E. eugeniae, and Artemia salina following a 12-day treatment period. Moreover, in the histopathological evaluation no discernible harm was observed in the gut tissues of E. eugeniae, including the lumen and epithelial cells, as well as the muscles, setae, nucleus, mitochondria, and coelom. The present findings provide clear evidence that M. rileyi fungal conidia can be used as the foundation for the development of effective bio-insecticides to combat the pupae of S. litura and S. frugiperda agricultural pests.

Physiological response of Metarhizium rileyi with linoleic acid supplementation

Metarhizium rileyi has a broad biocontrol spectrum but is highly sensitive to abiotic factors. A Colombian isolate M. rileyi Nm017 has shown notorious potential against Helicoverpa zea. However, it has a loss of up to 22 % of its conidial germination after drying, which limits its potential as a biocontrol agent and further commercialization. Conidial desiccation resistance can be enhanced by nutritional supplements, which promotes field adaptability and facilitates technological development as a biopesticide. In this study, the effect of culture medium supplemented with linoleic acid on desiccation tolerance in Nm017 conidia was evaluated. Results showed that using a 2 % linoleic acid-supplemented medium increased the relative germination after drying by 41 % compared to the control treatment, without affecting insecticidal activity on H. zea. Also, the fungus increased the synthesis of trehalose, glucose, and erythritol during drying, independently of linoleic acid use. Ultrastructural analyses of the cell wall-membrane showed a loss of thickness by 22 % and 25 %, in samples obtained from 2 % linoleic acid supplementation and the control, respectively. Regarding its morphological characteristics, conidia inner area from both treatments did not change after drying. However, conidia from the control had a 24 % decrease in length/width ratio, whereas there was no alteration in conidia from acid linoleic. The average value of dry conidia elasticity coefficient from linoleic acid treatment was 200 % above the control. Medium supplementation with linoleic acid is a promising fermentation strategy for obtaining more tolerant conidia without affecting production and biocontrol parameters, compatible solutes synthesis, or modifying its cell configuration.

First Report of <i>Metarhizium Rileyi</i> Infecting Fall Army Worm <i>Spodoptera Frugiperda</i> (J E Smith) From Nepal

The fall army worm (FAW) Spodoptera frugiperda (Noctuidae: Lepidoptera) is an invasive polyphagous pest that prefers maize crop in the newly invaded regions like Africa, Asia, Australasia, and some Pacific Islands and was recorded in Nepal in the year 2019. Surveys were conducted in the maize fields to collect various natural enemies for utilization in the management of FAW. Several larvae infected with an unidentified fungus were collected and subjected to morphological and molecular analysis for identification as Metarhizium rileyi. In bioassay studies we observed percent larval mortality at 1x108 conidia/ml suspension. This is the first report of M. rileyi infecting S. frugiperda from Nepal.

Pathogenicity, infection process, physiological and biochemical effects of Metarhizium rileyi against Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) larvae

BackgroundMetarhizium rileyi is an important entomopathogenic fungus which has a wide range of host pests. In this work, the virulence of M. rileyi EFNL-08 against 3rd instar larvae of the fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), was quantified. Additionally, the infection process and aspects of the host immunological response were described in the laboratory.ResultsBioassay results proved that M. rileyi was highly virulent to 3rd instar S. frugiperda larvae with 98.33% mortality at 1 × 108 conidia/ml. Scanning electron microscopy was used to monitor morphological aspects of the infection process. When hyphal bodies (Hbs) of M. rileyi were injected into the hemocoel of host, they were not recognized by the host’s immune system as invaders. There were nonsignificant differences in the hemocytes and phenoloxidase activity between the infected and control larvae at the initial 30 h, indicating that fungus successfully avoids the attack from the immune system. However, it inhibited the enzyme activity at the latest stage when Hbs reached a high density. After infection with M. rileyi, the activity of glutathione-S-transferase (GST) of S. frugiperda larvae presented a significant upward trend, while the activity of acetylcholinesterase (AchE) initially increased, followed by a decrease, and eventually stabilized. However, the activity of both detoxification enzymes in the control group showed slight fluctuations in the initial stage, and then stabilized at a low level.ConclusionObtained results provided new insights into the virulence and potential physiological responses of M. rileyi. This provides ideas for further development of novel and efficient entomopathogenic fungi (EPF) for pest control.

Status of fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera : Noctuidae) and its natural enemies at major maize growing areas of Haveri district

Fall armyworm (Spodoptera frugiperda) belongs to the family Noctuidae which has got economic importance as polyphagous and extreme pest of many important crops, including maize in India and elsewhere.In this context, roving survey was conducted on two cropping seasons at fortnightly interval during kharif and rabi of 2019-20 to know the status of fall armyworm in all the seven talukas of Haveri district viz., Hirekerur, Ranebennur, Byadagi, Haveri, Shiggaon, Savanur and Hangal. The results revealed that the mean larval population and per cent infestation of fall armyworm was ranged from 0.30 to 0.44 larvae per plant and 23.10 to 33.77 per cent, respectively in different talukas surveyed. In overall view Haveri district registered the mean larval population and per cent infestation of 0.37 larvae per plant and 28.99 per cent, respectively, in kharif and rabi. During the study period, it was observed for two different species of parasitoids viz., Campoletis chlorideae (Hymenoptera: Ichneumonidae) and Exorist axanthaspis (Diptera:Tachinidae) were parasitizing FAW larvae. Along with parasitoids, one entomopathogenic fungi, Metarhizium rileyi was known to infect the larvae which was collected during the survey period.

Population Dynamics of Fall Armyworm, Spodoptera frugiperda and its Natural Enimies in Maize

Fall armyworm (Spodoptera frugiperda) is one of the polyphagous invasive insect to India, initially reported from Karnataka. A roving survey was conducted during two cropping seasons at fortnightly interval at kharif and rabi of 2019-2020 to know the status of the pest in Haveri district. The results revealed that the mean larval population and per cent infestation of fall armyworm was ranged from 0.30 to 0.44 larvae per plant and 23.10 to 33.77 per cent, respectively. In the study period, parasitisation by two larval parasitoids viz., Campoletis chlorideae (Hymenoptera: Ichneumonidae) and Exorista xanthaspis (Diptera: Tachinidae) and infection by an entomopathogenic fungi, Metarhizium rileyi were also observed. The rainfall (r = -0.889) was only parameter having significantly negative influence on pest incidence.

Pathogenicity of Metarhizium rileyi (Hypocreales: Clavicipitaceae) against Tenebrio molitor (Coleoptera: Tenebrionidae).

Tenebrio molitor L., also known as the mealworm, is a polyphagous insect pest that infests various stored grains worldwide. Both the adult and larval stages can cause significant damage to stored grains. The present study focused on isolating entomopathogenic fungi from an infected larval cadaver under environmental conditions. Fungal pathogenicity was tested on T. molitor larvae and pupae for 12 days. Entomopathogenic fungi were identified using biotechnological methods based on their morphology and the sequence of their nuclear ribosomal internal transcribed spacer (ITS). The results of the insecticidal activity indicate that the virulence of fungi varies between the larval and pupal stages. In comparison to the larval stage, the pupal stage is highly susceptible to Metarhizium rileyi, exhibiting 100% mortality rates after 12 days (lethal concentration 50[LC50] = 7.8 × 106 and lethal concentration 90(LC90) = 2.1 × 1013 conidia/mL), whereas larvae showed 92% mortality rates at 12 days posttreatment (LC50 = 1.0 × 106 and LC90 = 3.0 × 109 conidia/mL). The enzymatic analyses revealed a significant increase in the levels of the insect enzymes superoxide dismutase (4.76-10.5 mg-1) and glutathione S-transferase (0.46-6.53 mg-1) 3 days after exposure to M. rileyi conidia (1.5 × 105 conidia/mL) compared to the control group. The findings clearly show that M. rileyi is an environmentally friendly and effective microbial agent for controlling the larvae and pupae of T. molitor.

Genetic diversity of the entomopathogenic fungus Metarhizium rileyi based on de novo microsatellite markers

Epizootics of the entomopathogenic fungus Metarhizium rileyi regulate lepidopteran populations in soybean, cotton, and peanut agroecosystems to the point that insecticide applications could be unnecessary. However, the contribution and how different strains operate during the epizootic are unknown. Several unanswered questions remain: 1. How many genotypes of M. rileyi are present during an epizootic? 2. Which genotype is the most common among them? 3. Are the genotypes involved in annual epizootics at the same location the same? Therefore, the development of molecular markers to accurately identify these genotypes is very important to answer these questions. SSR primers were designed by prospecting in silico to discriminate genotypes and infer the genetic diversity of M. rileyi isolates from the collection kept at Embrapa Soybean. We tested 13 SSR markers on 136 isolates to identify 43 clones and 12 different genetic clusters, with genetic diversity ranging from Hs = 0.15 (cluster I) to Hs = 0.41 (cluster IV) and an average diversity of 0.24. No clusters were categorically distinguished based on hosts or geographical origin using Bayesian clustering analysis. Nonetheless, some clusters comprised most of the isolates with a common geographic origin; for example, cluster VIII was mainly composed of isolates from Central-western Brazil, cluster II from Southern Brazil, and cluster XII from Quincy, Northern Florida, in the United States. Underrepresented regions (few isolates) from Pacific Island nations of Japan, the Philippines, and Indonesia (specifically from Java) were placed into clusters IX and X. Although the analyzed isolates displayed evidence of clonal structure, the genetic diversity indices suggest a potential for the species to adapt to different environmental conditions.

Metarhizium rileyi with broad-spectrum insecticidal ability confers resistance against phytopathogens and insect pests as a phytoendophyte.

Entomophagous fungi (EPF) not only directly kill insect pests, but also colonize plants and improve their resistance against pests. However, most previous research has focused on Beauveria bassiana and Metarhizium anisopliae, and there are few reports on whether other EPF can enhance resistance against pests via endogenous colonization. Herein, an EPF strain was isolated from diseased larvae of Spodoptera litura in a soybean field, and subjected to genome-wide sequencing at the chromosomal level. The pathogenicity of the isolate toward various pest insects was evaluated, and the ability to colonize plants and induce resistance against phytopathogens and insect pests was tested. The purified isolate was identified as M. rileyi and designated MrS1Gz1-1. Biological assays revealed its strong pathogenicity toward five insect pests belonging to Lepidoptera and Hemiptera. Furthermore, the strain inhibited the growth of soil-borne plant disease caused by Sclerotinia sclerotiorum in vitro. It colonized plants as an endophyte via soil application, thereby inducing plant resistance-related genes against phytopathogen infection, and it disrupted the feeding selectivity of S. litura larvae. M. rileyi MrS1Gz1-1 has potential as a broad-spectrum microbial control agent that can induce resistance against phytopathogens and insect pests feeding as an endotype. The complete genome provides a valuable resource for exploring host interactions. © 2024 Society of Chemical Industry.

Endophytic Fungi-Mediated Defense Signaling in Maize: Unraveling the Role of WRKY36 in Regulating Immunity against Spodoptera frugiperda.

Seed priming with beneficial endophytic fungi is an emerging sustainable strategy for enhancing plant resistance against insect pests. This study examined the effects of Beauvaria bassiana Bb20091317 and Metarhizium rileyi MrCDTLJ1 fungal colonization on maize growth, defence signalling, benzoxazinoid levels and gene expression. The colonization did not adversely affect plant growth but reduced larval weights of Spodoptera frugiperda. Maize leaves treated with M. rileyi exhibited higher levels of jasmonic acid, jasmonoyl-Isoleucine, salicylic acid, and indole acetic acid compared to control. B. bassiana and M. rileyi accelerated phytohormone increase upon S. frugiperda herbivory. Gene expression analysis revealed modulation of benzoxazinoid biosynthesis genes. We further elucidated the immune regulatory role of the transcription factor zmWRKY36 using virus-induced gene silencing (VIGS) in maize. zmWRKY36 positively regulates maize immunity against S. frugiperda, likely by interacting with defense-related proteins. Transient overexpression of zmWRKY36 in tobacco-induced cell death, while silencing in maize reduced chitin-triggered reactive oxygen species burst, confirming its immune function. Overall, B. bassiana and M. rileyi successfully colonized maize, impacting larval growth, defense signalling, and zmWRKY36-mediated resistance. This sheds light on maize-endophyte-insect interactions for sustainable plant protection.

Performance of Metarhizium rileyi Nm017: nutritional supplementation to improve production and quality conidia

This study aimed to analyze the effect of nutritional supplements on improving conidia production of Metarhizium rileyi Nm017 at laboratory scale (yields of conidia/substrate and biomass/substrate, and substrate consumption). Also, the influence on quality parameters were evaluated (germination at 36 and 48 h, enzymatic activity, and insecticidal activity on Helicoverpa zea). Six treatments (T1–T6) were assessed and all of them reached maximum conidia concentration after 7 days fermentation, a feasible production timetable. Yields from treatment T6 (yeast extract + V8 juice) were 1.5–threefold higher than the other treatments. Conidia from T6 reached germinations of 56% and 12% at 36 and 48 h, respectively, higher than T1 (without supplements), which had the lowest values found. M. rileyi conidia obtained from treatment T6 had the highest enzymatic activity (0.45 U chitinase g−1, 0.28 U lipase g−1, and 1.29 U protease g−1). However, treatments with the highest conidia yields and enzymatic activity were not positively correlated to the efficacy against H. zea. When M. rileyi was produced on T5 (yeast hydrolysate + V8 juice), conidia were 35% more virulent than treatment T6. The findings evidenced the noticeable impact of nutritional substrate amended for conidia production and quality. This work showed the relevance of insecticidal activity assessment as a selection criterion in the mass production development of a biocontrol agent.