Inhibitory effect of 10 natural phenolic compounds on Fusarium verticillioides. A structure–property–activity relationship study

Antioxidant and antimicrobial activities of Salsola imbricata methanolic extract and its phytochemical characterization

Methanolic extract from Salsola imbricata was investigated for its phytochemical content, antioxidant, and antimicrobial properties against phytopathogenic fungi and bacteria. Phytochemical analysis revealed the presence of saponin, tannins, and alkaloids with 1.25%, 18.8 mg catechin/g of extract, and 9.12%, respectively. Total flavonoid content was 20.8 mg quercetin equivalent/g while total phenolic content was 202 mg gallic acid equivalent/g. Antioxidant activity using the 2,2-diphenyl-1-picrylhydrazyl assay resulted in an IC50 value of 48.61 µg/mL, while the phosphomolybdenum method yielded a value of 215.43 mg ascorbic acid equivalent/g of extract. The highest phenolic acids detected in the extract were gallic acid (712.97 µg/g), syringic acid (742.7 µg/g), and caffeic acid (474.70 µg/g) according to high-performance liquid chromatography analysis. Palmitic acid (28.38%) dominated the fatty acids identified by gas chromatography-mass spectrometry, while stigmasterol (8.34%) was the most abundant steroid. At a concentration of 3 mg/mL, the extract showed strong antibacterial activity against Pectobacterium carotovorum (10.50 mm), Ralstonia solanacearum (9.93 mm), and Pectobacterium atrosepticum (8.37 mm). Additionally, the extract significantly suppressed fungal growth of Rhizoctonia solani (38.22%) and Fusarium oxysporum (33.56%) but showed lower activity toward Botrytis cinerea (13.33%) at 5 mg/mL. In conclusion, S. imbricata extract exhibited promising antioxidant and antimicrobial properties, making it a potential candidate for further exploration in agricultural applications.

Lignin-based monophenolic model compounds in L-tyrosine derivative synthesis via tyrosine phenol lyase

Tyrosine phenol lyase (TPL) synthesises L-tyrosine derivatives from monophenols, pyruvate and ammonia. Production of such high-value aromatic chemicals from biomass-derived raw materials is of great interest. In this study, six monophenols (guaiacol, phenol, o-cresol, m-cresol, catechol and syringol) were chosen based on the structure of lignin and were studied as substrates in the enzymatic reaction. Single monophenol reactions (SMR) and binary monophenol reactions (BMR) with guaiacol were carried out. TPL-M379V was found to be selective towards guaiacol (84.5 % conv.). The highest single activity was measured towards phenol (93.9 % conv.). However, the enzyme preferred guaiacol over phenol in the BMRs. Syringol was found to be inert in the reaction, whereas catechol had an inhibitory effect on the enzymatic reaction, in addition to causing degradation of all the substrates in the medium. Doubling the guaiacol concentration in the SMR did not significantly increase the production of 3-O-methyldopa (conv. 45.9 %). However, in the binary reaction systems the total monophenol conversions were higher with guaiacol and phenol (total 62.4 %) or o-cresol (total 57.1 %). This indicates possible substrate/product specific inhibition. The study provides new data on activity, selectivity and inhibitory effects of monophenols in the synthetic reaction catalysed by TPL-M379V, especially in mixed-substrate reactions.

Mycotoxigenic Fusarium species and zearalenone concentration in commercial maize kernels in northern Ghana

The fungal genus Fusarium contains many toxigenic pathogens of maize with associated yield losses, reduction of grain quality, and accumulation of mycotoxins in harvested grains. To determine zearalenone (ZEN) concentration and identify the various Fusarium species in commercial maize grains, a survey of 75 maize samples, collected from 11 market centers in the five regions in northern Ghana was identified based on morphological characteristics, sequence analysis of the internal transcribed spacer region, and polymerase chain reaction using species-specific primers. ZEN levels were determined using HPLC. ZEN contamination was recorded in 33.3% of the maize samples, with concentrations ranging from 0.61 to 3.05 µg/kg. Based on VERT1/2 and TEF 1-α sequencing, F. verticillioides was the most prevalent species in the studied samples: 40.35% from the Upper East Region, 28.07% from the North East Region, 19.30% from the Upper West Region, 10.53% from the Savannah Region, and 1.75% for the Northern Region. Other fungal species found were F. equiseti and F. solani. A higher number of the Fusarium isolates were found in white maize (609 isolates from 27 samples) compared to yellow maize (225 isolates from 23 samples).

Anti-oomycete activities from essential oils and their major compounds on Phytophthora infestans

Botanicals are various plant-based products like plant extracts or essential oils. Anti-fungal activities of selected essential oils were tested on the pathogen causing potato and tomato late blight (Phytophthora infestans). Tests to evaluate anti-oomycete activities of commercial essential oils and their major compounds were carried out in vitro in microplate in liquid media. Anti-oomycete activities on Phytophthora infestans strain were obtained from essential oils/major compounds: Eucalyptus citriodora/citronellal; Syzygium aromaticum (clove)/eugenol; Mentha spicata/D-Carvone, L-Carvone; Origanum compactum/carvacrol; Satureja montana (savory)/carvacrol; Melaleuca alternifolia (tea tree)/terpinen-4-ol, and Thymus vulgaris/thymol. As an active substance of mineral origin, copper sulfate was chosen as a control. All selected essential oils showed an anti-oomycete activity calculated with IC50 indicator. The essential oils of clove, savory, and thyme showed the best anti-oomycete activities similar to copper sulfate, while oregano, eucalyptus, mint, and tea tree essential oils exhibited significantly weaker activities than copper sulfate. Clove essential oil showed the best activity (IC50 = 28 mg/L), while tea tree essential oil showed the worst activity (IC50 = 476 mg/L). For major compounds, three results were obtained: they were statistically more active than their essential oils (carvacrol for oregano, D- and L-Carvone for mint) or as active as their essential oils sources (thymol for thyme, carvacrol for savory, terpinen-4-ol for tea tree) or less active than their original essential oils (eugenol for clove, citronellal for eucalyptus). Microscopical observations carried out with the seven essential oils showed that they were all responsible for a modification of the morphology of the mycelium. The results demonstrated that various essential oils show different anti-oomycete activities, sometimes related to a major compound and sometimes unrelated, indicating that other compounds must play a role in total anti-oomycete activity.

Antifungal activity of essential oils and their combinations against storage fungi

We aimed to evaluate the fungicidal activity of essential oils (EOs) from Baccharis dracunculifolia (Asteraceae), Baccharis uncinella (Asteraceae), Mentha arvensis (Lamiaceae), Salvia officinalis (Lamiaceae), Melaleuca alternifolia (Myrtaceae), and Cymbopogon nardus (Poaceae) in the in vitro control of mycotoxin-producing strains of Aspergillus niger, Aspergillus nomius, Aspergillus flavus, and Fusarium graminearum. EOs' chemical composition was analyzed by gas chromatography-mass spectrometry, and a total of 19, 21, 18, 20, 17, and 15 compounds were identified in B. dracunculifolia, B. uncinella, S. officinalis, M. arvensis, M. alternifolia, and C. nardus EOs, respectively. Contact and volatilization bioassays were performed, for which M. alternifolia and C. nardus EOs had the greatest fungicidal effect (> 90%). Therefore, these EOs were evaluated for minimum inhibitory concentration, medium inhibitory concentration, and sporulation. Effects from the combined use of EOs were also evaluated. EOs interacted in combination, displaying an additive effect against F. graminearum and A. flavus and an antagonistic effect against the remaining isolates. We conclude that C. nardus EO was effective in the control of storage pathogens and that combined EOs can improve their antifungal effects.

Plants from a semi-arid environment as a source of phytochemicals against Fusarium crown and foot rot in zucchini

Fusarium crown and foot rot, caused by F. solani f. sp. cucurbitae, are major fungal diseases affecting zucchini and other cucurbits. Despite the efficacy of synthetic fungicides, their health and environmental hazards have highlighted the urgent need for safer alternatives, such as phytochemical-based biocides. Owing to the upregulation of the plant secondary metabolism under stressful conditions, bioprospecting in harsh environments could reveal ore plants for bioactive metabolites. In this study, thirteen wild plants were collected from their natural habitat in a semiarid environment (Yanbu, Saudi Arabia) and extracted to obtain phenolics rich extracts. Total polyphenols, flavonoids, antioxidant capacities and the antifungal activities of the extracts against a pathogenic isolate of F. solani were assessed. Fusarium solani was isolated from infected zucchini and characterized by scanning electron microscopy. Hierarchical clustering analysis of the phytochemical screening and in vitro bioactivity revealed that Rosmarinus officinalis, Pulicaria crispa, Achillea falcata and Haloxylon salicornicum were the richest in polyphenols and the most powerful against F. solani. Further, the extracts of these four plants significantly decreased the disease incidence in zucchini, where P. crispa was the premier. Interestingly, results of transmission electron microscopy revealed that extract of P. crispa, as a representative of the powerful group, induced ultrastructural disorders in fungal cells. Therefore, this study suggests the use of R. officinalis, P. crispa, A. falcata and H. salicornicum grown in semi-arid environments as ore plants to develop phytochemical-based biocides against Fusarium crown and foot rot.

Isoeugenol affects expression pattern of conidial hydrophobin gene RodA and transcriptional regulators MedA and SomA responsible for adherence and biofilm formation in Aspergillus fumigatus

Aspergillus fumigatus is one of the major pathogenic fungal species, causing life-threatening infections. Due to a limited spectrum of available antifungals, exploration of new drug targets as well as potential antifungal molecules has become pertinent. Rodlet layer plays an important role in adherence of fungal conidia to hydrophobic cell surfaces in host, which also leads to A. fumigatus biofilm formation, contributing factor to fungal pathogenicity. From decades, natural sources have been known for the development of new active molecules. The present study investigates effect of isoeugenol on genes responsible for hydrophobins (RodA), adhesion as well as biofilm formation (MedA and SomA) of A. fumigatus. Minimum inhibitory concentrations (MIC and IC₅₀) of isoeugenol against A. fumigatus were determined using broth microdilution assay. The IC₅₀ results showed reduced hydrophobicity and biofilm formation as well as eradication after treatment with the compound and electron micrograph data corroborated these findings. The qRT-PCR showed a significant downregulation of genes RodA, MedA, SomA and pksP involved in hydrophobicity and biofilm formation. SwissADME studies potentiated drug-like propensity for isoeugenol which formed four hydrogen bonds with low binding energy (− 4.54 kcal/mol) at the catalytic site of RodA protein studied via AutoDock4. Hence, the findings conclude that isoeugenol inhibits conidial hydrophobicity and biofilm formation of A. fumigatus and further investigations are warranted in this direction.

Bioprospecting Phenols as Inhibitors of Trichothecene-Producing Fusarium: Sustainable Approaches to the Management of Wheat Pathogens

Fusarium spp. are ubiquitous fungi able to cause Fusarium head blight and Fusarium foot and root rot on wheat. Among relevant pathogenic species, Fusarium graminearum and Fusarium culmorum cause significant yield and quality loss and result in contamination of the grain with mycotoxins, mainly type B trichothecenes, which are a major health concern for humans and animals. Phenolic compounds of natural origin are being increasingly explored as fungicides on those pathogens. This review summarizes recent research activities related to the antifungal and anti-mycotoxigenic activity of natural phenolic compounds against Fusarium, including studies into the mechanisms of action of major exogenous phenolic inhibitors, their structure-activity interaction, and the combined effect of these compounds with other natural products or with conventional fungicides in mycotoxin modulation. The role of high-throughput analysis tools to decipher key signaling molecules able to modulate the production of mycotoxins and the development of sustainable formulations enhancing potential inhibitors' efficacy are also discussed.

Ammoides pusilla Essential Oil: A Potent Inhibitor of the Growth of Fusarium avenaceum and Its Enniatin Production

Enniatins are mycotoxins produced by Fusarium species contaminating cereals and various agricultural commodities. The co-occurrence of these mycotoxins in large quantities with other mycotoxins such as trichothecenes and the possible synergies in toxicity could lead to serious food safety problems. Using the agar dilution method, Ammoides pusilla was selected among eight Tunisian plants for the antifungal potential of its essential oil (EO) on Fusarium avenaceum mycelial growth and its production of enniatins. Two EO batches were produced and analyzed by GC/MS-MS. Their activities were measured using both contact assays and fumigant tests (estimated IC50 were 0.1 µL·mL⁻¹ and 7.6 µL·L⁻¹, respectively). The A. pusilla EOs and their volatiles inhibited the germination of spores and the mycelial growth, showing a fungistatic but not fungicidal activity. The accumulation of enniatins was also significantly reduced (estimated IC50 were 0.05 µL·mL⁻¹ for the contact assays and 4.2 µL·L⁻¹ for the fumigation assays). The most active batch of EO was richer in thymol, the main volatile compound found. Thymol used as fumigant showed a potent fungistatic activity but not a significant antimycotoxigenic activity. Overall, our data demonstrated the bioactivity of A. pusilla EO and its high potential to control F. avenaceum and its enniatins production in agricultural commodities.

Comparison of antifungal activity of essential oils of clove, lemongrass and thyme for natural preservation of dried apricots

Currently, the majority of fresh apricots destined for the production of dried apricots undergo sulphur oxide fumigation before drying to protect the fruit against fungal spoilage. To eliminate the use of sulphite, packaging assisted with essential oil is a promising strategy to increase shelf-life of dried apricots since it does not impact its flavor characteristics. In this study, three essential oils were selected: clove, lemongrass and thyme. They were screened for antifungal activity against Eurotium spp. with different methods: micro- and macro-dilution and agar-diffusion. Growth/no-growth data were used to develop models for all three methods. Clove exerted the strongest antifungal activity with an inhibitory concentration of 0.075%, 0.035% and 0.05% through respectively micro-dilution, macro-dilution and agar diffusion. For thyme the following values were obtained: 0.775%, 0.070% and 0.100%. This means that the antifungal activity of thyme is 10 times lower in micro-dilution and 2 times lower in macro-dilution and agar diffusion compared to clove. Through micro-dilution, lemongrass was found to have the second highest antifungal activity (0.25%). When used in the volatile atmosphere of dried apricots and in macro-dilution, the antifungal activity of lemongrass was the lowest, with respective values of > 0.200% and 0.105% for G/NG prediction.

Molecular Docking and Comparative Inhibitory Efficacy of Naturally Occurring Compounds on Vegetative Growth and Deoxynivalenol Biosynthesis in Fusarium culmorum

The fungal pathogen Fusarium culmorum causes Fusarium head blight in cereals, resulting in yield loss and contamination of the grain by type B trichothecene mycotoxins such as deoxynivalenol (DON), and its acetylated derivatives. Synthesis of trichothecenes is driven by a trichodiene synthase (TRI5) that converts farnesyl pyrophosphate (FPP) to trichodiene. In this work, 15 naturally occurring compounds that belong to the structural phenol and hydroxylated biphenyl classes were tested in vitro and in planta (durum wheat) to determine their inhibitory activity towards TRI5. In vitro analysis highlighted the fungicidal effect of these compounds when applied at 0.25 mM. Greenhouse assays showed a strong inhibitory activity of octyl gallate 5, honokiol 13 and the combination propyl gallate 4 + thymol 7 on trichothecene biosynthesis. Docking analyses were run on the 3D model of F. culmorum TRI5 containing the inorganic pyrophosphate (PPi) or FPP. Significant ligand affinities with TRI-PPi and TRI-FPP were observed for the same sites for almost all compounds, with 1 and 2 as privileged sites. Octyl gallate 5 and honokiol 13 interacted almost exclusively with sites 1 and 2, by concurrently activating strong H-bonds with common sets of amino acids. These results open new perspectives for the targeted search of naturally occurring compounds that may find practical application in the eco-friendly control of FHB in wheat.

Volatile phenolics: A comprehensive review of the anti-infective properties of an important class of essential oil constituents

Historically, essential oils and their lead molecules have been extensively recognised for their anti-infective properties. In this context, certain volatile phenolics (VPs) have emerged as important antimicrobial compounds with excellent inhibitory activity against pathogenic bacteria and fungi, which further extends to drug-resistant and biofilm-forming micro-organisms. In this review, we aim to collate and discuss a number of published papers on the anti-infective activities of naturally occurring VPs with special emphasis on eugenol, isoeugenol, thymol and carvacrol, using Scopus Web of Science and PubMed databases. The biosynthesis and extraction of these VPs are discussed, while particular attention is given to their broad-spectrum antimicrobial activity and the mechanisms of action. We highlight combinational studies of the VPs with other phytocompounds and with commercially available drugs, which may be a promising and a rewarding future approach to combat antimicrobial resistance. These VPs alone, or concomitantly with other compounds or drugs, have the potential to be incorporated into different formulations for biomedical applications. An in-depth assessment of 2310 articles retrieved from the Scopus database spanning a 35-year period indicated 23.1% increase in global publication growth in VPs anti-infective research, with authors from Italy, Portugal and Austria dominating the research landscape. The dominant areas of investigations are identified as antimicrobial activity, antibacterial mechanism of action, antifungal mechanism of action, extraction methods and phytochemistry, use in the food industry, and for oral and dental anti-infective activity. Specific research areas, which require future attention include; antituberculosis research, nanoparticle formulation of antimicrobial active VP molecules, preclinical and clinical trials. The antimicrobial testing of isoeugenol was found to be the least studied of the VPs and this requires further attention.

Effect of Naturally Occurring Compounds on Fumonisin Production and fum Gene Expression in Fusarium verticillioides

Fusarium verticillioides, one of the most common pathogens in maize, is responsible for yield losses and reduced kernel quality due to contamination by fumonisins (FBs). Two F. verticillioides isolates that differed in their ability to produce FBs were treated with a selection of eight natural phenolic compounds with the aim of identifying those that were able to decrease toxin production at concentrations that had a limited effect on fungal growth. Among the tested compounds, ellagic acid and isoeugenol, which turned out to be the most effective molecules against fungal growth, were assayed at lower concentrations, while the first retained its ability to inhibit toxin production in vitro, the latter improved both the fungal growth and FB accumulation. The effect of the most effective phenolic compounds on FB accumulation was also tested on maize kernels to highlight the importance of appropriate dosages in order to avoid conditions that are able to promote mycotoxin biosynthesis. An expression analysis of genes involved in FB production allowed more detailed insights into the mechanisms underlying the inhibition of FBs by phenolic compounds. The expression of the fum gene was generally down-regulated by the treatments; however, some treatments in the low-producing F. verticillioides strain up-regulated fum gene expression without improving FB production. This study showed that although different phenolic compounds are effective for FB reduction, they can modulate biosynthesis at the transcription level in opposite manners depending on strain. In conclusion, on the basis of in vitro and in vivo screening, two out of the eight tested phenols (ellagic acid and carvacrol) appear to be promising alternative molecules for the control of FB occurrence in maize.

Essential Oils and Their Application in Food Safety

Food industries are facing a great challenge due to contamination of food products with different microbes such as bacteria, fungi, viruses, parasites, etc. These microbes deteriorate food items by producing different toxins during pre- and postharvest processing. Mycotoxins are one of the most potent and well-studied toxic food contaminants of fungal origin, causing a severe health hazard to humans. The application of synthetic chemicals as food preservatives poses a real scourge in the present scenario due to their bio-incompatibility, non-biodegradability, and environmental non-sustainability. Therefore, plant-based antimicrobials, including essential oils, have developed cumulative interest as a potential alternative to synthetic preservatives because of their ecofriendly nature and generally recognized as safe status. However, the practical utilization of essential oils as an efficient antimicrobial in the food industry is challenging due to their volatile nature, less solubility, and high instability. The recent application of different delivery strategies viz. nanoencapsulation, active packaging, and polymer-based coating effectively addressed these challenges and improved the bioefficacy and controlled release of essential oils. This article provides an overview of essential oils for the preservation of stored foods against bacteria, fungi, and mycotoxins, along with the specialized mechanism of action and technological advancement by using different delivery systems for their effective application in food and agricultural industries smart green preservative.

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%), β-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.

Isoeugenol and Hybrid Acetamides against Candida albicans Isolated from the Oral Cavity

Isougenol is a phytoconstituent found in several essential oils. Since many natural products are potent antimicrobials, the synthesis of hybrid molecules-combining the chemical skeleton of the phytochemical with synthetic groups-can generate substances with enhanced biological activity. Based on this, the objective of this study was to evaluate the antifungal activity of isoeugenol and hybrid acetamides against Candida albicans isolated from the oral cavity. The methodologies used were the determination of minimum inhibitory concentration (MIC), minimum fungicidal concentration (MFC), action on fungal micromorphology, interaction test with nystatin by the checkerboard method and molecular docking study with important enzymes in the maintenance of fungal viability. The synthetic molecules did not demonstrate significant antifungal activity in vitro. The isoeugenol MIC and MFC varied between 128 and 256 µg/mL, being the phytoconstituent able to interfere in the formation of blastoconid and chlamydoconid structures, important in the pathogenic process of the species. The molecular docking study revealed that isoeugenol is a potential inhibitor of the enzymes 14-α-demethylase and delta-14-sterol reductase, interfering in the fungal cell membrane biosynthesis. Thus, this research provides clearer expectations for future pharmacological studies with isoeugenol and derived molecules, aiming at its therapeutic application against infections caused by Candida spp.

Prediction of critical properties of sulfur-containing compounds: New QSPR models

In this study, new models have been proposed for the prediction of different critical properties (critical temperature (T_C), critical pressure (P_C), critical volume (V_C), and acentric factor (ω)) of the sulfur-containing compounds based on quantitative structure-property relationship (QSPR). An extensive data set containing experimental data of over 130 different sulfur-containing compounds was employed. Enhanced Replacement Method (ERM) was applied for subset variable selection. Based on ERM selected descriptors, two different models, including linear model and genetic programming (GP) based non-linear model have been proposed for each critical property. The predicted values of each target were in good agreement with the experimental data. For GP-based models, the values of the coefficient of determination (R²) were 0.936, 0.976, 0.990, and 0.917 for T_C, P_C, V_C, and ω, respectively. After revisiting the available QSPR models, it was found that the domain of applicability of new models has been expanded.

Wheat straw vinegar: A more cost-effective solution than chemical fungicides for sustainable wheat plant protection

Fusarium head blight (FHB), caused by the fungal pathogen Fusarium graminearum, is a destructive and widespread wheat disease. Chemical fungicides are becoming less effective at reducing the disease severity of FHB, and there is a need to find a more effective, low-cost natural product. A by-product of the pyrolysis of wheat straw is a condensate known as wheat straw vinegar, which was hypothesized to be an effective F. graminearum inhibitor in wheat. The organic and mineral compositions of wheat straw vinegar were analyzed. The results of GC-MS indicated that the major organic compounds in wheat straw vinegar are phenolics and acetic acid. The main inorganic elements in the liquid were K, Ca, S and Mg. A bio-test of wheat straw vinegar showed strong antifungal activity on F. graminearum growth and production of deoxynivalenol (DON) with an EC₅₀ (concentration for 50% of maximal effect) value of 3.1 μl ml^-1. Field tests showed that the application of wheat straw vinegar diluted 200-fold significantly decreased the wheat FHB infection rate and DON content by 66% and 69%, respectively. The control efficacy of wheat straw vinegar at a dilution of 200-fold was similar to that of typical chemical fungicide applications. The use of wheat straw vinegar may increase farmers' income by reducing the net fungicide costs. Therefore, wheat straw vinegar has high potential as a natural fungicide for the control of FHB and can reduce the dependence on synthetic fungicides.

Essential Oils as Potential Alternative Biocontrol Products against Plant Pathogens and Weeds: A Review

Naturally produced by aromatic plants, essential oils (EO) contain a wide range of volatile molecules, including mostly secondary metabolites, which possess several biological activities. Essential oils properties such as antioxidant, antimicrobial and anti-inflammatory activities are known for a long time and hence widely used in traditional medicines, cosmetics and food industries. However, despite their effects against many phytopathogenic fungi, oomycetes and bacteria as well as weeds, their use in agriculture remains surprisingly scarce. The purpose of the present review is to gather and discuss up-to-date biological activities of EO against weeds, plant pathogenic fungi, oomycetes and bacteria, reported in the scientific literature. Innovative methods, potentially valuable to improve the efficiency and reliability of EO, have been investigated. In particular, their use towards a more sustainable agriculture has been discussed, aiming at encouraging the use of alternative products to substitute synthetic pesticides to control weeds and plant diseases, without significantly affecting crop yields. An overview of the market and the recent advances on the regulation of these products as well as future challenges to promote their development and wider use in disease management programs is described. Because of several recent reviews on EO insecticidal properties, this topic is not covered in the present review.

The Inhibitory Potential of Selected Essential Oils on Fusarium spp. Growth and Mycotoxins Biosynthesis in Maize Seeds

Owing to their rich chemical composition, essential oils (EOs) have many interesting properties, including antimicrobial activities. The presence of Fusarium and their secondary metabolites, mycotoxins, in cereal crops is a serious problem in agriculture, which consequently affects food quality. The aim of the present study was to investigate the effects of selected EOs on the growth of Fusarium graminearum and F. culmorum and the biosynthesis of mycotoxins in maize seeds. Chromatographic analysis of ergosterol as a fungal growth indicator showed a significant inhibition of Fusarium growth (83.24–99.99%) compared to the control samples, which as a consequence resulted in a reduction in mycotoxin concentrations. The addition of cinnamon, palmarosa, orange, and spearmint EOs was shown to be the most effective in reducing zearalenone concentration (99.10–99.92%). Deoxynivalenol analysis confirmed a very high reduction of this compound at the application all tested EOs (90.69–100%). The obtained results indicated that EOs have a great potential to inhibit growth of Fusarium fungi as well as reduce the concentration of mycotoxins in maize seed.

Phenol-based millipede defence: antimicrobial activity of secretions from the Balkan endemic millipede Apfelbeckia insculpta (L. Koch, 1867) (Diplopoda: Callipodida)

Millipedes use an array of chemical compounds to defend themselves from predator attack. These chemical substances can have additional roles, i.e. defence against various pathogens. We evaluated the efficacy of the defensive secretion of Apfelbeckia insculpta (L. Koch, 1867) against bacteria, yeasts, and filamentous fungi. The tested secretion consisted of two compounds, p-cresol and phenol, and showed antibacterial, antibiofilm, and antifungal potential against all selected microorganisms. The most sensitive bacterium in our study was Pseudomonas aeruginosa, while the tested defensive secretion manifested the lowest activity against Escherichia coli. The defensive secretion of A. insculpta also showed an ability, albeit mild, to suppress biofilm formation by P. aeruginosa. Among the tested yeasts, Candida albicans and C. krusei were the most susceptible and most resistant species, respectively. Finally, the concentration of extracts obtained from the tested defensive secretion needed to achieve an antifungal effect was lowest in the case of Cladosporium cladosporioides. Fusarium verticillioides and Penicillium rubens were the micromycetes most resistant to the tested secretion. Our results indicate that antibacterial activity of the defensive secretion of A. insculpta is similar to or slightly weaker than that of streptomycin, while comparison with antimycotics showed that the tested millipede secretion has stronger activity than fluconazole, but weaker activity than nystatin and ketoconazole. The present study corroborates previous findings indicating that the defensive secretions of millipedes can have different roles apart from antipredator protection and are effective against pathogenic microorganisms.

Plant antimicrobial polyphenols as potential natural food preservatives

BACKGROUND

The growing demand for natural food preservatives in the last decade has promoted investigations on their application for preserving perishable foods. In this context, the present review is focused on discussing the prospective application of plant extracts containing phenolics or isolated plant phenolics as natural antimicrobials in foods. Plant essential oils are outside the scope of this review since utilization of their antimicrobial activity for food preservation has been extensively reviewed.

RESULTS

Although the exact antimicrobial mechanisms of action of phenolic compounds are not yet fully understood, it is commonly acknowledged that they have diverse sites of action at the cellular level. Antimicrobial phenolics can be added directly to the formulation of perishable food products or incorporated into food-contact materials to release them in the immediate zone of perishable foods. Edible coatings or active food packaging materials can thus be used as carriers of plant bioactive compounds.

CONCLUSION

These materials could be an interesting delivery system to improve the stability of phenolics in foods and to improve the shelf life of perishable foods. This review will thus provide an overview of current knowledge of the antimicrobial activity of phenolic-rich plant extracts and of the promises and limits of their exploitation for the preservation of perishable foods. © 2018 Society of Chemical Industry.

Growth modeling to control (in vitro) Fusarium verticillioides and Rhizopus stolonifer with thymol and carvacrol

The aim of this study was to evaluate the antifungal activity (in vitro) of thymol and carvacrol alone or in mixtures against Fusarium verticillioides and Rhizopus stolonifer, and to obtain primary growth models. Minimal inhibitory concentration (MIC) was evaluated with fungal radial growth with thymol or carvacrol concentrations (0-1600mg/l). Mixtures were evaluated using concentrations below MIC values. Radial growth curves were described by the modified Gompertz equation. MIC values of carvacrol were 200mg/l for both fungi. Meanwhile, MIC values of thymol were between 500 and 400mg/l for F. verticillioides and R. stolonifer, respectively. A synergistic effect below MIC concentrations for carvacrol (100mg/l) and thymol (100-375mg/l) was observed. Significant differences (p<0.05) between the Gompertz parameters for the antimicrobial concentrations and their tested mixtures established an inverse relationship between antimicrobial concentration and mycelial development of both fungi. Modified Gompertz parameters can be useful to determine fungistatic concentrations.

Growth, hydrolases and ultrastructure of Fusarium oxysporum as affected by phenolic rich extracts from several xerophytic plants

Fusarium oxysporum, the causal agent of rot and wilt diseases, is one of the most detrimental phytopathogens for the productivity of many economic crops. The present study was conducted to evaluate the potentiality of some xerophytic plants as eco-friendly approach for management of F. oxysporum. Phenolic rich extracts from five plants namely: Horwoodia dicksoniae, Citrullus colocynthis, Gypsophila capillaris, Pulicaria incisa and Rhanterium epapposum were examined in vitro. The different extracts showed high variability in their phenolic and flavonoid contents as well as total antioxidant capacity. A strong positive correlation existed between the antifungal activity of the tested extracts and their contents of both total phenolics and flavonoids (r values are 0.91 and 0.82, respectively). Extract of P. incisa was the most effective in reducing the mycelial growth (IC₅₀=0.92mg/ml) and inhibiting the activities of CMCase, pectinase, amylase and protease by 36, 42, 58 and 55%, respectively. The high performance liquid chromatography analysis of P. incisa extract revealed the presence of eight phenolic acids along with five polyphenolic compounds. The flavonol, quercetin and its glycosides rutin and quercetrin were the most abundant followed by the phenolic acids, t-cinnamic, caffeic, ferulic and vanillic. P. incisa extract not only affects the growth and hydrolases of F. oxysporum but also induces ultrastructure changes in the mycelium, as revealed by transmission electron microscopy. To our knowledge, this is the first study to investigate the mechanisms underlying the antifungal activity of P. incisa.

Ligninolytic Activity at 0 °C of Fungi on Oak Leaves Under Snow Cover in a Mixed Forest in Japan

Despite the importance of litter decomposition under snow cover in boreal forests and tundra, very little is known regarding the characteristics and functions of litter-decomposing fungi adapted to the cold climate. We investigated the decomposition of oak leaves in a heavy snowfall forest region of Japan. The rate of litter weight loss reached 26.5% during the snow cover period for 7 months and accounted for 64.6% of the annual loss (41.1%). Although no statistically significant lignin loss was detected, decolourization portions of oak leaf litter, which was attributable to the activities of ligninolytic fungi, were observed during snow cover period. This suggests that fungi involved in litter decomposition can produce extracellular enzymes to degrade lignin that remain active at 0 °C. Fungi were isolated from oak leaves collected from the forest floor under the snow layer. One hundred and sixty-six strains were isolated and classified into 33 operational taxonomic units (OTUs) based on culture characteristics and nuclear rDNA internal transcribed spacer (ITS) region sequences. To test the ability to degrade lignin, the production of extracellular phenoloxidases by isolates was quantified at 0 °C. Ten OTUs (9 Ascomycota and 1 Basidiomycota) of fungi exhibited mycelial growth and ligninolytic activity. These results suggested that some litter-decomposing fungi that had the potential to degrade lignin at 0 °C significantly contribute to litter decomposition under snow cover.

Natural Phenolic Inhibitors of Trichothecene Biosynthesis by the Wheat Fungal Pathogen Fusarium culmorum: A Computational Insight into the Structure-Activity Relationship

A model of the trichodiene synthase (TRI5) of the wheat fungal pathogen and type-B trichothecene producer Fusarium culmorum was developed based on homology modelling with the crystallized protein of F. sporotrichioides. Eight phenolic molecules, namely ferulic acid 1, apocynin 2, propyl gallate 3, eugenol 4, Me-dehydrozingerone 5, eugenol dimer 6, magnolol 7, and ellagic acid 8, were selected for their ability to inhibit trichothecene production and/or fungal vegetative growth in F. culmorum. The chemical structures of phenols were constructed and partially optimised based on Molecular Mechanics (MM) studies and energy minimisation by Density Functional Theory (DFT). Docking analysis of the phenolic molecules was run on the 3D model of F. culmorum TRI5. Experimental biological activity, molecular descriptors and interacting-structures obtained from computational analysis were compared. Besides the catalytic domain, three privileged sites in the interaction with the inhibitory molecules were identified on the protein surface. The TRI5-ligand interactions highlighted in this study represent a powerful tool to the identification of new Fusarium-targeted molecules with potential as trichothecene inhibitors.

Structure-Activity Relationships of Antimicrobial Gallic Acid Derivatives from Pomegranate and Acacia Fruit Extracts against Potato Bacterial Wilt Pathogen

Bacterial wilts of potato, tomato, pepper, and or eggplant caused by Ralstonia solanacearum are among the most serious plant diseases worldwide. In this study, the issue of developing bactericidal agents from natural sources against R. solanacearum derived from plant extracts was addressed. Extracts prepared from 25 plant species with antiseptic relevance in Egyptian folk medicine were screened for their antimicrobial properties against the potato pathogen R. solancearum by using the disc-zone inhibition assay and microtitre plate dilution method. Plants exhibiting notable antimicrobial activities against the tested pathogen include extracts from Acacia arabica and Punica granatum. Bioactivity-guided fractionation of A. arabica and P. granatum resulted in the isolation of bioactive compounds 3,5-dihydroxy-4-methoxybenzoic acid and gallic acid, in addition to epicatechin. All isolates displayed significant antimicrobial activities against R. solanacearum (MIC values 0.5-9 mg/ml), with 3,5-dihydroxy-4-methoxybenzoic acid being the most effective one with a MIC value of 0.47 mg/ml. We further performed a structure-activity relationship (SAR) study for the inhibition of R. solanacearum growth by ten natural, structurally related benzoic acids.

Characteristics of estrogenic/antiestrogenic activities during the anoxic/aerobic biotreatment process of simulated textile dyeing wastewater

HOA and HON were key fractions involved in increasing antiestrogenic activity and humic/fulvic acid in them could mask estrogenic activity.

Bioactivities of Ketones Terpenes: Antifungal Effect on F. verticillioides and Repellents to Control Insect Fungal Vector, S. zeamais

Maize is one the most important staple foods in the world. However, numerous pests, such as fungal pathogens, e.g., Fusarium verticillioides, and insects, such as Sitophlilus zeamais, attack maize grains during storage. Many F. verticillioides strains produce fumonisins, one of the most important mycotoxin that causes toxic effects on human and animal health. This situation is aggravated by the insect fungal vector, Sitophlilus zeamais, which contributes to the dispersal of fungal spores, and through feeding damage, provide entry points for fungal infections. The aim of this study was to evaluate in vitro bioassays, the antifungal activity on F. verticillioides M3125 and repellent effects against S. zeamais of ketone terpenes. In addition, we performed Quantitative structure-activity relationship (Q-SAR) studies between physico-chemical properties of ketone terpenes and the antifungal effect. Thymoquinone was the most active compound against F. verticillioides (Minimum Inhibitory Concentration, MIC: 0.87) affecting the lag phase and the growth rate showing a total inhibition of growth at concentration higher than 2 mM (p < 0.05). The Q-SAR model revealed that the antifungal activity of ketone compounds is related to the electronic descriptor, Pi energy. Thymoquinone showed a strong repellent effect (-77.8 ± 8.5, p < 0.001) against S. zeamais. These findings make an important contribution to the search for new compounds to control two stored pests of maize.

Effect of Selected Volatiles on Two Stored Pests: The Fungus Fusarium verticillioides and the Maize Weevil Sithophilus zeamais

New agronomic practices and technology enabled Argentina a larger production of cereal grains, reaching a harvest yield of 26.5 million metric tons of maize, of which, about 40% was exported. However, much of the maize production is lost annually by the attack of fungi and insects (2.6 million tons). In this study, the antifungal effect of selected volatiles on Fusarium verticillioides, its mycotoxin production, and the repellent and insecticidal activities against the weevill Sithophilus zeamais, an insect vector of F. verticillioides, were evaluated. The compounds tested were (2E)-2-hexenal, (2E)-2-nonenal, (2E,6Z)-2,6-nonadienal, 1-pentanol, 1-hexanol, 1-butanol, 3-methyl-1-butanol, pentanal, 2-decanone, and 3-decanone, which occur in the blend of volatile compounds emitted by various cereal grains. The most active antifungals were the aldehydes (2E)-2-nonenal, (2E)-2-hexenal, and (2E,6Z)-2,6-nonadienal (minimum inhibitory concentration values of <0.03, 0.06, and 0.06 mM, respectively). The occurrence of fumonisin B1 also was prevented because these compounds completely inhibited fungal growth. The best insecticidal fumigant activities against the maize weevil were shown by 2-decanone and 3-decanone (lethal concentration ≤ 54.6 μL/L (<0.28 mM)). Although, all tested compounds showed repellent activity against S. zeamais at a concentration of 4 μL/L, (2E,6Z)-2,6-nonadienal was the most active repellent compound. These results demonstrate the potential of (2E,6Z)-2,6-nonadienal to be used as a natural alternative to synthetic pesticides on F. verticillioides and S. zeamais.

Inhibitory Effect of Natural Phenolic Compounds onAspergillus parasiticusGrowth

Considering the impact ofAspergillusspecies on crops, it appears to be highly desirable to apply strategies to prevent their growth, as well as to eliminate or reduce their presence in food products. For this reason, the aims of this investigation were to evaluate the effects of ten natural phenolic compounds on theAspergillus parasiticusgrowth and to determine which physicochemical properties are involved in the antifungal activity. According to the results of minimum inhibitory concentration (MIC) values of the individual compounds, isoeugenol, carvacrol, and thymol were the most active phenolic components (1.26 mM, 1.47 mM, and 1.50 mM, resp.), followed by eugenol (2.23 mM). On the other hand, creosol, p-cresol, o-cresol, m-cresol, vanillin, and phenol had no effects on fungal development. Logarithm of the octanol/water partition coefficient (log P), refractivity index (RI), and molar volume (MV) were demonstrated to be the descriptors that best explained the antifungal activity correlated to lipophilicity, reactivity of the components, and steric aspect. These findings make an important contribution to the search for new compounds with antifungal activity.

Natural and natural-like phenolic inhibitors of type B trichothecene in vitro production by the wheat (Triticum sp.) pathogen Fusarium culmorum

Fusarium culmorum, a fungal pathogen of small grain cereals, produces 4-deoxynivalenol and its acetylated derivatives that may cause toxicoses on humans or animals consuming contaminated food or feed. Natural and natural-like compounds belonging to phenol and hydroxylated biphenyl structural classes were tested in vitro to determine their activity on vegetative growth and trichothecene biosynthesis by F. culmorum. Most of the compounds tested at 1.5 or 1.0 mM reduced 3-acetyl-4-deoxynivalenol production by over 70% compared to the control, without affecting fungal growth significantly. Furthermore, several compounds retained their ability to inhibit toxin in vitro production at the lowest concentrations of 0.5 and 0.25 mM. Magnolol 27 showed fungicidal activity even at 0.1 mM. No linear correlation was observed between antioxidant properties of the compounds and their ability to inhibit fungal growth and mycotoxigenic capacity. A guaiacyl unit in the structure may play a key role in trichothecene inhibition.

In vitro activity of natural phenolic compounds against fluconazole-resistant Candida species: a quantitative structure-activity relationship analysis

AIMS

To evaluate the antifungal activity and to analyse the structure-activity relationship of eleven natural phenolic compounds against four Candida species which are resistant to fluconazole.

METHODS AND RESULTS

Four different species of Candida isolates were used: Candida albicans, Candida krusei, Candida tropicalis and Candida dubliniensis. The phenolic compound carvacrol showed the highest anti-Candida bioactivity, followed by thymol and isoeugenol. The obtained minimum inhibitory concentration (MIC) values obtained were used in a quantitative structure-activity relationship (QSAR) analysis where the electronic, steric, thermodynamic and topological descriptors served as dependent variables. According to the descriptors obtained in this QSAR study, the antifungal activity of phenols has a first action specific character which is based on their interaction with plasma or mitochondrial membranes. The second action is based on a steric descriptor-the maximal and minimal projection of the area-which could explain the inability of some phenolic compounds to be biotransformed to quinones methylene by Candida species.

CONCLUSIONS

According to the descriptors obtained in this QSAR study, the anti-Candida activity of ortho-substituted phenols is due to more than one action mechanism. The anti-Candida activity of phenolic compounds can be predicted by their molecular properties and structural characteristics.

SIGNIFICANCE AND IMPACT OF THE STUDY

These results could be employed to predict the anti-Candida activity of new phenolic compounds in the search for new alternatives or complementary therapies to combat against candidiasis.

Inhibition of Fusarium graminearum growth and mycotoxin production by phenolic extract from Spirulina sp

Fusarium graminearum is a fungal species complex pathogenic occurring worldwide, mainly associated with cereal crops. The most important Fusarium mycotoxins are fumonisins, zearalenone and trichothecenes. The availability of efficient control measures that are less harmful to both the environment and the consumers is urgent. For such, phenolic acids (PAs) from natural sources are known to reduce fungal contaminations. This work aimed to identify the PAs present in a culture extract of Spirulina algae (strain LEB-18) and evaluate its effect on mycelial growth rate, glucosamine level, amylase activity and mycotoxin production by four strains of two lineages of F. graminearum. Results showed that amendment of potato dextrose media with LEB-18 extract (3% w/v), which was mainly composed by gallic acid, greatly reduced radial growth of fungal colonies compared to media containing a single PA and the control. Also, average reductions of 40% and 62% in the glucosamine levels and the amylase activity were observed. In general, the LEB-18 extract and the PAs reduced mycotoxin concentration, with an average reduction of 68% for the trichothecene mycotoxins deoxynivalenol and nivalenol.