Impact of non-selective fungicides on the growth and production of ochratoxin A by Aspergillus ochraceus and A. carbonarius in barley-based medium

Potential use of machine learning methods in assessment of Fusarium culmorum and Fusariumproliferatum growth and mycotoxin production in treatments with antifungal agents

Fusarium-controlling fungicides are necessary to limit crop loss. Little is known about the effect of antifungal formulations at sub-lethal doses, and their interaction with abiotic factors, on Fusarium culmorum and F. proliferatum development and on zearalenone and fumonisin biosynthesis, respectively. In the present study different treatments based on sulfur, trifloxystrobin and demethylation inhibitor fungicides (cyproconazole, tebuconazole and prothioconazole) under different environmental conditions, in Maize Extract Medium, are assayed in vitro. Several machine learning methods (neural networks, random forest and extreme gradient boosted trees) have been applied for the first time for modeling growth of F. culmorum and F. proliferatum and zearalenone and fumonisin production, respectively. The most effective treatment was prothioconazole, 250 g/L + tebuconazole, 150 g/L. Effective doses of this formulation for reduction or total growth inhibition ranged as follows ED₅₀ 0.49-1.70, ED₉₀ 2.57-6.02 and ED₁₀₀ 4.0-8.0 µg/mL, depending on the species, water activity and temperature. Overall, the growth rate and mycotoxin levels in cultures decreased when doses increased. Some treatments in combination with certain a_w and temperature values significantly induced toxin production. The extreme gradient boosted tree was the model able to predict growth rate and mycotoxin production with minimum error and maximum R² value.

Heuchera Creme Brulee and Mahogany Medicinal Value under Water Stress and Oligosaccharide (COS) Treatment

Food borne pathogens cause serious human illnesses and diseases and their control using natural bioactive compounds becomes essential for the progress of agricultural and food industries. Developing novel tools to enhance the medicinal values of traditional horticultural medicinal crops is one of the promising methods for achieving food borne pathogens control. In this study, oligosaccharide water solutions were applied to Heuchera Creme Brulee and Mahogany subjected to a normal irrigation interval (2 days) or to prolonged irrigation intervals (6 days) for 6 weeks. Plant morphological, physiological, and metabolic markers associated with the bioactivity of leaf extracts against selected microbes. Oligosaccharide-treated plants showed significant increases in all morphological parameters during normal and prolonged irrigation intervals as compared to those of the controls. Morphological improvement associated with a significant increase in chlorophyll, carbohydrates, proline, K, Ca, phenols, and free and total ascorbate and antioxidants. Superoxide dismutase, catalase, and ascorbate peroxidase activities were higher, while H₂O₂ accumulated to a lower extent in oligosaccharide-treated plants. These morphological and metabolic changes associated with increased antibacterial and antifungal activities of leaf extracts and their activities were comparable to antibiotics and antifungal agents (minimum inhibitory concentrations values were 0.5 -0.20 mg⁻¹mL for bacteria and 0.08 -0.20 mg⁻¹mL for fungi in Mahogany). The application of oligosaccharide and/or water stress might be of great value for producing natural bioactive compounds for food borne pathogens control.

Risk management of ochratoxigenic fungi and ochratoxin A in maize grains by bioactive EVOH films containing individual components of some essential oils

Aspergillus steynii and Aspergillus tubingensis are possibly the main ochratoxin A (OTA) producing species in Aspergillus section Circumdati and section Nigri, respectively. OTA is a potent nephrotoxic, teratogenic, embryotoxic, genotoxic, neurotoxic, carcinogenic and immunosuppressive compound being cereals the first source of OTA in the diet. In this study bioactive ethylene-vinyl alcohol copolymer (EVOH) films containing cinnamaldehyde (CINHO), linalool (LIN), isoeugenol (IEG) or citral (CIT) which are major components of some plant essential oils (EOs) were produced and tested against A. steynii and A. tubingensis growth and OTA production in partly milled maize grains. Due to the favourable safety profile, these bioactive compounds are considered in the category "GRAS". The study was carried out under different water activity (0.96 and 0.99 a_w), and temperature (24 and 32 °C) conditions. ANOVA showed that class of film, fungal species, a_w and temperature and their interactions significantly affected growth rates (GR), ED₅₀ and ED₉₀ and the doses for total fungal growth inhibition and OTA production. The most effective EVOH films against both species were those containing CINHO. ED₅₀, ED₉₀ and doses for total growth and OTA inhibition were 165-405, 297-614, 333-666 μg of EVOH-CINHO/plate (25 g of maize grains), respectively, depending on environmental conditions. The least efficient were EVOH-LIN films. ED₅₀, ED₉₀ and doses for total growth and OTA inhibition were 2800->3330, >3330 and >3330 μg of EVOH-LIN/plate (25 g of maize grains), respectively. The effectiveness of the bioactive films increased with increasing doses. Overall, A. tubingensis was less sensitive to treatments than A. steynii. Depending on the species, a_w and temperature affected GR and OTA production in a different way. In A. steynii cultures, optimal growth occurred at 0.96 a_w and 32 °C while optimal OTA production happened at 0.99 a_w and 32 °C. In A. tubingensis cultures optimal growth happened at 0.99 a_w and 32 °C, although the best conditions for OTA production were 0.99 a_w and 24 °C. Thus, these species can be very competitive in warm climates and storage conditions. The EVOH-CINHO films followed by EVOH-IEG and EVOH-CIT films, designed in this study and applied in vapour phase, can be potent antifungal agents against A. steynii and A. tubingensis and strong inhibitors of OTA biosynthesis in maize grains at very low doses. This is the first study on the impact that interacting environmental conditions and bioactive films containing individual components of EOs have on the growth of these ochratoxigenic fungi and on OTA production in maize grains.

Assessment of azole fungicides as a tool to control growth of Aspergillus flavus and aflatoxin B1 and B2 production in maize

Aspergillus flavus is a highly aflatoxin (AF)-producing species infecting maize and other crops. It is dominant in tropical regions, but it is also considered an emerging problem associated with climate change in Europe. The aim of this study was to assess the efficacy of azole fungicides (prochloraz, tebuconazole and a 2:1 (w/w) mixture of prochloraz plus tebuconazole) to control the growth of A. flavus and AF production in yeast-extract-sucrose (YES) agar and in maize kernels under different water activities (a_w) and temperatures. Aflatoxins B₁ and B₂ were determined by LC with fluorescence detection and post-column derivatisation of AFB₁. In YES medium and maize grains inoculated with conidia of A. flavus, the growth rate (GR) of the fungus and AFB₁ and AFB₂ production were significantly influenced by temperature and treatment. In YES medium and maize kernels, optimal temperatures for GR and AF production were 37 and 25°C, respectively. In maize kernels, spore germination was not detected at the combination 37ºC/0.95 a_w; however, under these conditions germination was found in YES medium. All fungicides were more effective at 0.99 than 0.95 a_w, and at 37 than 25ºC. Fungicides effectiveness was prochloraz > prochloraz plus tebuconazole (2:1) > tebuconazole. AFs were not detected in cultures containing the highest fungicide doses, and only very low AF levels were found in cultures containing 0.1 mg l^-1 prochloraz or 5.0 mg l^-1 tebuconazole. Azoles proved to be highly efficient in reducing A. flavus growth and AF production, although stimulation of AF production was found under particular conditions and low-dosage treatments. Maize kernels were a more favourable substrate for AF biosynthesis than YES medium. This paper is the first comparative study on the effects of different azole formulations against A. flavus and AF production in a semi-synthetic medium and in maize grain under different environmental conditions.

Impact of bioactive packaging systems based on EVOH films and essential oils in the control of aflatoxigenic fungi and aflatoxin production in maize

Aspergillus flavus and A. parasiticus are the most common fungal species associated with aflatoxin (AF) contamination of cereals, especially maize, and other agricultural commodities. AFB_1, the most frequent and toxic metabolite, is a powerful hepatotoxic, teratogenic and mutagenic compound. Effective strategies to control these fungal species and AFs in food and feed are required. Active packaging film containing essential oils (EO) is one of the most innovative food packaging concepts. In this study, ethylene-vinyl alcohol (EVOH) copolymer films incorporating EO from Origanum vulgare (ORE), Cinnamomum zeylanicum (CIN) or their major active constituents, carvacrol (CAR) and cinnamaldehyde (CINHO), respectively, were developed and assayed to control growth of A. flavus and A. parasiticus and AF production in maize grains under different a_w and temperature regimens. EO doses assayed in cultures were in the range 0.25-4.0mg/Petri dish. The factors a_w, temperature, type of EVOH-EO film and fungal species significantly influenced the ED₅₀ values of all assayed films. Growth rate (GR) of both species was usually higher at 0.99 than at 0.96 a_w and at 37°C than at 25°C. However, the contrary was found with regard to AF production. The order of efficacy of EVOH-EO films to control growth of both species and AF production was EVOH-CINHO>EVOH-CAR>EVOH-ORE>EVOH-CIN. The effective dose (ED₅₀) (mg EO/plate) for EVOH-CINHO and EVOH-CIN films against A. flavus were in the ranges of 0.125 and 2.475-3.500 and against A. parasiticus in the ranges of 0.121-0.133 and 2.275-3.625, respectively. Under the assayed conditions, the ED₉₀ for EVOH-CINHO film were 0.22-0.23mg/plate for both species. It was the most effective bioactive film to control fungal growth (vapour phase) and AF production, regardless of a_w and temperature. This is the first study about the impact that interacting environmental conditions and bioactive EVOH-CINHO, EVOH-ORE, EVOH-CIN EVOH-CAR films have on the growth of aflatoxigenic fungi and on AF production in maize grains.

Effect of Fungicides on Growth and Ochratoxin A Production by Aspergillus carbonarius from Brazilian Wine Grapes

Prevention in the field of mycotoxin-producing fungi is the most effective strategy for controlling the presence of mycotoxins in foods. Chemical fungicides are widely used to protect crops, so their implications on mycotoxin production need to be considered. Therefore, the aim of this study was to evaluate the effect in vitro and on grapes of five fungicides commonly used on grape cultures in Brazil on Aspergillus carbonarius growth and ochratoxin A (OTA) production. At the doses recommended by manufacturers, most fungicides significantly reduced A. carbonarius growth and OTA production in vitro, whereas this effect was influenced by the type of fungicide, dose, and temperature. Temperature was the main factor that influenced the effectiveness of fungicides. In general, at 15°C, fungicides showed the greatest reduction on fungal growth and OTA production. Fungicide effect on grapes was different to that on a semisynthetic grape medium. All fungicide doses were not effective at controlling A. carbonarius in grapes. Thus, the direct effect of fungicides on grapes must be studied to obtain a better approximation of field conditions. The results indicate that the use of fungicides at the doses recommended by manufacturers is better than the application at low doses. This study showed that at the lowest doses, where fungal growth is not inhibited, fungicides positively stimulate OTA production.

OTA-Grapes: A Mechanistic Model to Predict Ochratoxin A Risk in Grapes, a Step beyond the Systems Approach

Ochratoxin A (OTA) is a fungal metabolite dangerous for human and animal health due to its nephrotoxic, immunotoxic, mutagenic, teratogenic and carcinogenic effects, classified by the International Agency for Research on Cancer in group 2B, possible human carcinogen. This toxin has been stated as a wine contaminant since 1996. The aim of this study was to develop a conceptual model for the dynamic simulation of the A. carbonarius life cycle in grapes along the growing season, including OTA production in berries. Functions describing the role of weather parameters in each step of the infection cycle were developed and organized in a prototype model called OTA-grapes. Modelling the influence of temperature on OTA production, it emerged that fungal strains can be shared in two different clusters, based on the dynamic of OTA production and according to the optimal temperature. Therefore, two functions were developed, and based on statistical data analysis, it was assumed that the two types of strains contribute equally to the population. Model validation was not possible because of poor OTA contamination data, but relevant differences in OTA-I, the output index of the model, were noticed between low and high risk areas. To our knowledge, this is the first attempt to assess/model A. carbonarius in order to predict the risk of OTA contamination in grapes.

In vitro effect of some fungicides used in cultivation of Capsicum spp. on growth and ochratoxin A production by Aspergillus species

The present study aimed to assess the effect of some pre-harvest fungicides commonly used in Capsicum fruit production on growth and ochratoxin A production of three Aspergillus species found in Capsicum powder. Aspergillus tubingensis, Aspergillus ochraceus and Aspergillus westerdijkiae, previously isolated from paprika and chilli, were inoculated on yeast extract sucrose agar and paprika extract agar supplemented with different fungicides at their recommended dosage rates, and incubated at 20 and 30 °C during 7 days. Radial growth was measured after 3, 5 and 7 days and ochratoxin A production was determined by high-performance liquid chromatography with fluorescence detection on day 7. Dodine 40% and mancozeb 80% were the most effective fungicides in inhibiting growth and ochratoxin A production, regardless of the fungal strain tested or temperature conditions. Whereas the application of fungicides could be very attractive in reducing the mycotoxigenic fungal load, it can also stimulate ochratoxin A production in some cases.