Volatilome of the maize phytopathogenic fungus Fusarium verticillioides: potential applications in diagnosis and biocontrol.

BACKGROUND: Fusarium verticillioides is a maize fungal phytopathogen and a producer of volatile organic compounds (VOCs) and fumonisin B1 (FB1). Our aim was to study the volatilome, conidial production, ergosterol and FB1 biosynthesis in maize cultures over a 30-day incubation period (5, 10, 15, 20, 25, 30 days post inoculation [DPI]). The effect of pure VOCs on the same parameters was then evaluated to study their potential role as biocontrol agents. RESULTS: In total, 91 VOCs were detected, with volatile profiles being more similar between 5 and 10 DPI compared with 15, 20, 25 and 30 DPI. Ergosterol content increased steadily with incubation time, and three growth stages were identified: a lag phase (0 to 15 DPI), an exponential phase (15 to 20 DPI) and a stationary phase (20 to 30 DPI). The maximum concentration of FB1 was detected at 25 (0.030 µg FB1/µg ergosterol) and 30 DPI (0.037 µg FB1/µg ergosterol), whereas conidial production showed a maximum value at 15 DPI (4.3 ± 0.2 × 105 conidia/µg ergosterol). Regarding pure VOCs, minimal inhibitory concentration values ranged from 0.3 mm for 4-hexen-3-one to 7.4 mm for 2-undecanone. Pure VOCs reduced radial growth, conidial production and ergosterol and FB1 biosynthesis. CONCLUSIONS: The marked resemblance between VOC profiles at 5 and 10 DPI suggests that they could act as early indicators of fungal contamination, particularly 4-ethylguaiacol, 4-ethyl-2-methoxyanisole, heptanol and heptyl acetate. On the other hand, their role as inhibitors of fungal growth and FB1 biosynthesis prove their great potential as safer alternatives to control phytopathogenic fungi. © 2024 Society of Chemical Industry.

Sulcatone as a Plant-Derived Volatile Organic Compound for the Control of the Maize Weevil and Its Associated Phytopathogenic Fungi in Stored Maize.

Stored maize is frequently attacked by different pests, such as insects and microorganisms. The aim of the present study was to evaluate the bioactivities of sulcatone (6-methyl-5-hepten-2-one) against the maize weevil Sitophilus zeamais and the phytopathogenic fungi Fusarium verticillioides, Aspergillus flavus, and A. parasiticus. Sulcatone showed a strong repellent effect with a maximum value of -92.1 ± 3.2% at 40 µM in two-choice olfactometer bioassays and an LC95 value of 17.2 µL/L air (95% 16.5-18.1) in a fumigant toxicity experiment. The antifungal effect of sulcatone was evaluated through the fumigant method, reporting MIC values of 3.5, 3.8, and 3.9 mM for F. verticillioides, A. parasiticus, and A. flavus, respectively. Additionally, a silo-bag experiment containing all pests was conducted to evaluate the potential use of sulcatone in a real storage system. Sulcatone caused 71.69 ± 1.57% weevil mortality in silo-bags and proved to be effective as a fungicidal and antimycotoxigenic agent since both ergosterol and fumonisin B1 content were significantly reduced by 60% in silo-bags containing sulcatone. This study demonstrated that sulcatone has the potential to be used for the control of both insects and fungi of stored maize, without affecting the germination of grains.

Exploring Contact Toxicity of Essential Oils against Sitophilus zeamais through a Meta-Analysis Approach.

Sitophilus zeamais is a primary pest of maize. Our aim was to perform a qualitative review and meta-analyses with 56 scientific articles published from 1 January 2000 to 1 October 2022 dealing with direct (topical application) and indirect (impregnation of essential oils, EOs, onto filter paper or maize grains) contact toxicity of EOs against S. zeamais. Three independent meta-analyses of single means of LD50 (direct contact) and LC50 (indirect contact) were conducted using a random effect model. Essential oils more frequently evaluated were those belonging to Asteraceae, Apiaceae, Lamiaceae, Myrtaceae, Piperaceae, and Rutaceae. The LC50 global mean values were 33.19 µg/insect (CI95 29.81-36.95) for topical application; 0.40 µL/cm2 (CI95 0.25-0.65) for filter paper indirect contact; and 0.50 µL/g maize (CI95 0.27-0.90) for maize grains indirect contact. The species Carum carvi, Salvia umbratica, Ilicium difengpi, Periploca sepium, Cephalotaxus sinensis, Murraya exotica, Rhododendron anthopogonoides, Ruta graveolens, Eucalyptus viminalis, Ocotea odorifera, Eucalyptus globulus, Eucalyptus dunnii, Anethum graveolens, Ilicium verum, Cryptocarya alba, Azadirachta indica, Chenopodium ambrosioides, Cupressus semperivens, Schinus molle, Piper hispidinervum, Mentha longifolia, and Croton pulegiodorus showed LC50 or LD50 values lower than the global means, indicating good insecticidal properties. Our results showed that EOs have great potential to be used as bioinsecticides against S. zeamais.

Effect of Carbon Sources on the Production of Volatile Organic Compounds by Fusarium verticillioides.

The aim of the present study was to evaluate the effect of different carbon sources on the hydrocarbon-like volatile organic compounds (VOCs) of Fusarium verticillioides strain 7600 through a Principal Component Analysis approach, and to explore their diesel potential by using data from the literature. The fungus was cultivated in GYAM culture medium, and five carbon sources were evaluated: glucose, sucrose, xylose, lactose, and fructose. The VOCs were collected using a close-loop apparatus and identified through GC-MS. The same profile of 81 VOCs was detected with all treatments, but with different relative percentages among carbon sources. The production of branched-chain alkanes (30 compounds) ranged from 25.80% to 38.64%, straight-chain alkanes (12 compounds) from 22.04% to 24.18%, benzene derivatives (12 compounds) from 7.48% to 35.58%, and the biosynthesis of branched-chain alcohols (11 compounds) was from 6.82% to 16.71%, with lower values for the remaining groups of VOCs. Our results show that F. verticillioides has the metabolic potential to synthesize diesel-like VOCs. Further research should include the optimization of culture conditions other than carbon sources to increase the production of certain groups of VOCs.

Fungal diversity and mycotoxins detected in maize stored in silo-bags: a review.

Silo-bags are hermetic storage systems that inhibit fungal growth because of their atmosphere with low humidity, as well as low pH and O2 concentrations, and a high CO2 concentration. If a silo-bag with stored maize loses its hermetic nature, it favors the development of fungi and the production of mycotoxins. To the best of our knowledge, this is the first review on the diversity of fungal species and mycotoxins that were reported in maize stored under the environmental conditions provided by silo-bags. The genera Penicillium, Aspergillus and Fusarium were found more frequently, whereas Acremonium spp., Alternaria sp., Candida sp., Cladosporium sp., Debaryomyces spp., Epiconum sp., Eupenicillium spp., Eurotium sp., Eurotium amstelodami, Hyphopichia spp., Hyphopichia burtonii, Moniliella sp., Wallemia sp. and genera within the orden Mucorales were reported less recurrently. Despite finding a great fungal diversity, all of the studies focused their investigations on a small group of toxins: fumonisins (FBs), aflatoxins (AFs), deoxynivalenol (DON), zearalenone (ZEA), patulin (PAT), toxin T2 (T2) and ochratoxin (OT). Of the FBs, fumonisin B1 and fumonisin B2 presented higher incidence percentages, followed by fumonisin B3 . Of the AFs, the only one reported was aflatoxin B1. The mycotoxins DON, ZEA and OT were found with lower incidences, whereas PAT and T2 were not detected. Good management practices of the silo-bags are necessary to achieve a hermetically sealed environment, without exchange of gases and water with the external environment during the storage period. © 2022 Society of Chemical Industry.

Insecticidal Activity of Essential Oils against Mealybug Pests (Hemiptera: Pseudococcidae): A Systematic Review and Meta-Analysis.

Most mealybugs of the Pseudococcidae family are important pests of agriculture and ornamental gardens. Our aim was to perform a review and meta-analysis on 14 published scientific articles on the insecticidal activity of essential oils (EOs) against mealybug species of the Pseudococcidae family. Data on (1) species, genus, families, and plant parts from which the EO was extracted; (2) the main compounds of each EO; (3) the highest and lowest concentrations tested; and (4) the application method used for the toxicological studies was collected from each study. The metafor package (R software) was used to perform a three-level random effects meta-analysis. The families Lamiaceae, Rutaceae, Myrtaceae, Zingiberaceae and Euphorbiaceae and the genera Citrus, Cymbopogon, Syzygium, Cinnamomum and Jatropha were the most used among the studies. According to the results from the meta-analyses, 13 out of 24 genera analyzed were effective against mealybugs. All methods were effective, but fumigation and indirect contact were the most frequently used methodologies. The results obtained from the present review and meta-analysis could be used for the potential development of natural biopesticide formulations against mealybugs belonging to the Pseudococcidae family.

Chemical composition and antifungal properties of commercial essential oils against the maize phytopathogenic fungus Fusarium verticillioides / Composición química y propiedades antifúngicas de aceites esenciales comerciales contra el hongo fitopatógeno de maíz Fusarium verticillioides

ABSTRACT The aim of the present study was to analyze the chemical composition ofCurcuma longa,Pimenta dioica,Rosmarinus officinalis, andSyzygiumaromaticumessential oils (EOs) and their antifungal and anti-conidiogenic activity againstFusarium verticillioides. The chemical profile of the EOs was determined by GC/MS. The antifungal and anti-conidiogenic activities were evaluated by the agar dilution method. The tested concentrations were 1000ppm, 500ppm, 250ppm and 125ppm.S. aromaticumEO exhibited the highest antifungal effect, followed byP. dioicaand to a lesser extentC. longa. The major compounds of these EOs were eugenol (88.70% inS. aromaticumand 16.70% inP. dioica), methyl eugenol (53.09% inP. dioica), and α-turmerone (44.70%), β-turmerone (20.67%), and Ar-turmerone (17.27%) inC. longa.Rosmarinus officinalispoorly inhibited fungal growth; however, it was the only EO that inhibited conidial production, with its major components being 1,8-cineole (53.48%), α-pinene (15.65%), and (−)-camphor (9.57%). Our results showed that some compounds are capable of decreasing mycelial growth without affecting sporulation, and vice versa. However, not all the compounds of an EO are responsible for its bioactivity. In the present work, we were able to identify different major compounds or mixtures of major compounds that were responsible for antifungal and anti-conidiogenic effects. Further experiments combining these pure components are necessary in order to achieve a highly bioactive natural formulation against the phytopathogenic fungusF. verticillioides.

RESUMEN El objetivo del presente estudio fue analizar la composición química de los aceites esenciales (AE) deCurcuma longa,Pimenta dioica,RosmarinusofficinalisySyzygiumaromaticum, y su actividad antifúngica y anti-esporuladora contraFusarium verticillioides. La composición de los AE se analizó por CG-EM. La actividad antifúngica y anti-esporuladora se evaluó a través del método de dilución en agar usando las siguientes concentraciones: 1.000, 500, 250 y 125ppm. El AE deS. aromaticumdemostró el mayor efecto antifúngico, seguido del deP. dioicay, en menor medida, delC. longa. Los compuestos principales de estos AE fueron eugenol (88,70% enS. aromaticumy 16,70% enP. dioica), metileugenol (53,09% enP. dioica) y α-turmerona (44,70%), β-turmerona (20,67%) y Ar-turmerona (17,27%) enC. longa. El AE deR. officinalisfue el que menor efecto inhibitorio presentó sobre el crecimiento fúngico, pero fue el único que inhibió la producción de conidias; sus principales componentes fueron 1,8-cineol (53,48%), α-pineno (15,65%) y (−)-alcanfor (9,57%). Nuestros resultados demostraron que algunos compuestos son capaces de disminuir el crecimiento del micelio deF. verticillioidessin afectar la esporulación, y vice versa. Sin embargo, no todos los compuestos de un AE son responsables de su bioactividad. En el presente trabajo, pudimos identificar diferentes compuestos o mezclas de compuestos que fueron responsables de los efectos antifúngicos y anti-esporuladores. Se necesitan nuevos experimentos que evalúen la combinación de estos compuestos puros para lograr una formulación bioactiva y de origen natural para el control deF. verticillioides.

Carbon sources to enhance the biosynthesis of useful secondary metabolites in Fusarium verticillioides submerged cultures.

Fusarium verticillioides is a prolific producer of useful secondary metabolites such as naphthoquinone pigments, monoterpenes, and sesquiterpenes, as well as the harmful mycotoxins fumonisins. A strategy to increase their production includes creating a proper nutritional environment that enables the fungus to produce the compounds of interest. The aim of the present work was to study the effect of different carbon sources (glucose, fructose, xylose, sucrose, and lactose) on secondary metabolites biosynthesis in F. verticillioides submerged cultures. The production of volatile terpenes was evaluated through gas chromatography coupled to mass spectrometry. The quantification and identification of pigments was conducted using a UV/VIS spectrophotometer and NMR spectrometer, respectively. The quantification of fumonisin B1 and fumonisin B2 was performed by high-performance liquid chromatography. Our results showed that the biosynthesis of naphthoquinone pigments, monoterpenes, and sesquiterpenes was highest in cultures with fructose (13.00 ± 0.71 mmol/g), lactose [564.52 × 10-11 ± 11.50 × 10-11 µg/g dry weight (DW)], and xylose (54.41 × 10-11 ± 1.55 × 10-11 µg/g DW), respectively, with fumonisin being absent or present in trace amounts in the presence of these carbon sources. The highest biosynthesis of fumonisins occurred in sucrose-containing medium (fumonisin B1: 7.85 × 103 ± 0.25 × 103 µg/g DW and fumonisin B2: 0.38 × 103 ± 0.03 × 103 µg/g DW). These results are encouraging since we were able to enhance the production of useful fungal metabolites without co-production with harmful mycotoxins by controlling the carbon source provided in the culture medium.

Chemical composition and antifungal properties of commercial essential oils against the maize phytopathogenic fungus Fusarium verticillioides.

The aim of the present study was to analyze the chemical composition of Curcuma longa, Pimenta dioica, Rosmarinus officinalis, and Syzygium aromaticum essential oils (EOs) and their antifungal and anti-conidiogenic activity against Fusarium verticillioides. The chemical profile of the EOs was determined by GC/MS. The antifungal and anti-conidiogenic activities were evaluated by the agar dilution method. The tested concentrations were 1000ppm, 500ppm, 250ppm and 125ppm. S. aromaticum EO exhibited the highest antifungal effect, followed by P. dioica and to a lesser extent C. longa. The major compounds of these EOs were eugenol (88.70% in S. aromaticum and 16.70% in P. dioica), methyl eugenol (53.09% in P. dioica), and α-turmerone (44.70%), ß-turmerone (20.67%), and Ar-turmerone (17.27%) in C. longa. Rosmarinus officinalis poorly inhibited fungal growth; however, it was the only EO that inhibited conidial production, with its major components being 1,8-cineole (53.48%), α-pinene (15.65%), and (-)-camphor (9.57%). Our results showed that some compounds are capable of decreasing mycelial growth without affecting sporulation, and vice versa. However, not all the compounds of an EO are responsible for its bioactivity. In the present work, we were able to identify different major compounds or mixtures of major compounds that were responsible for antifungal and anti-conidiogenic effects. Further experiments combining these pure components are necessary in order to achieve a highly bioactive natural formulation against the phytopathogenic fungus F. verticillioides.