Mycotoxin occurrence and Aspergillus flavus soil propagules in a corn and cotton glyphosate-resistant cropping systems

Soil Aspergillus Species, Pathogenicity and Control Perspectives

Five Aspergillus sections have members that are established agricultural pests and producers of different metabolites, threatening global food safety. Most of these pathogenic Aspergillus species have been isolated from almost all major biomes. The soil remains the primary habitat for most of these cryptic fungi. This review explored some of the ecological attributes that have contributed immensely to the success of the pathogenicity of some members of the genus Aspergillus over time. Hence, the virulence factors of the genus Aspergillus, their ecology and others were reviewed. Furthermore, some biological control techniques were recommended. Pathogenic effects of Aspergillus species are entirely accidental; therefore, the virulence evolution prediction model in such species becomes a challenge, unlike their obligate parasite counterparts. In all, differences in virulence among organisms involved both conserved and species-specific genetic factors. If the impacts of climate change continue, new cryptic Aspergillus species will emerge and mycotoxin contamination risks will increase in all ecosystems, as these species can metabolically adjust to nutritional and biophysical challenges. As most of their gene clusters are silent, fungi continue to be a source of underexplored bioactive compounds. The World Soil Charter recognizes the relevance of soil biodiversity in supporting healthy soil functions. The question of how a balance may be struck between supporting healthy soil biodiversity and the control of toxic fungi species in the field to ensure food security is therefore pertinent. Numerous advanced strategies and biocontrol methods so far remain the most environmentally sustainable solution to the control of toxigenic fungi in the field.

Influence of a glyphosate-based herbicide on growth parameters and aflatoxin B1 production by Aspergillus section Flavi on maize grains

Glyphosate-based herbicides (GBH) are the main pesticides applied worldwide on maize production. Glyphosate-resistant weeds led to the repeated application of high doses of the pesticide. In addition to environmental conditions, the presence of GBH affects the development of Aspergillus species and aflatoxin B1 (AFB1) production under in vitro conditions. The aim of this work was to evaluate the influence of a commercial GBH on growth and AFB1 production by Aspergillus flavus and Aspergillus parasiticus strains under different water activity (aW) conditions. The following concentrations of active ingredient glyphosate were evaluated: 20, 50, 200 and 500mM. The lag phase prior to growth and growth rate did not change at 20 and 50mM (that is, at field recommended doses) at 0.98 and 0.95 aW; however, at increasing GBH concentrations, between 200 and 500mM, the growth rate decreased at all aW conditions. In general, as the GBH concentration increased, AFB1 production decreased. However, a significant increase in toxin accumulation was found only at one of the aW conditions (0.95) at 21 days with 50mM of GBH in A. flavus and 20 and 50mM of GBH in A. parasiticus. These results show that, even though Aspergillus section Flavi growth did not increase, AFB1 production increased on maize grains at GBH concentrations similar to those of field recommended doses under favorable water availability and temperature conditions.

Effect of in vitro glyphosate on Fusarium spp. growth and disease severity in maize

BACKGROUND

Glyphosate (GP) is one of the main pesticides used for maize production. Fusarium sp. is a fungal genus with several phytopathogenic species and toxigenic features. In this study, the culturable soil mycota was evaluated using the surface-spray method. The effect of GP on the growth parameters (growth rate and lag phase) of Fusarium spp. was also tested on solid media conditioned with different water activities. Finally, the GP effect on disease severity caused by Fusarium sp. in maize seedlings was studied.

RESULTS

The results showed that Fusarium species are frequently isolated from GP-exposed soils. The GP concentrations tested had a significant effect on F. graminearum, F. verticillioides and F. oxysporum growth parameters on solid media. The pathogenicity tests showed that the disease severity of the maize seedlings significantly increased with increasing GP concentrations.

CONCLUSIONS

This study showed that Fusarium species are frequently isolated from pesticide-exposed soils and the GP concentrations tested had a significant effect both on growth parameters and disease severity in maize. This study provides an approach to the effect of GP on Fusarium sp. growth and pathogenicity that reinforces the importance of evaluating all the factors that could affect feed and food production. © 2019 Society of Chemical Industry.

Assessment of growth of Aspergillus spp. from agricultural soils in the presence of glyphosate

Agriculture is one of the bases of the Argentine economy. Glyphosate is undoubtedly one of the most important herbicides used. The increasing consumption and the efficiency of glyphosate-based herbicides have encouraged several studies on their persistence in soils, their effects on soil microbiota and their degradation processes. Fungi have been reported as being the main herbicide-degrading microorganisms as well as the most tolerant to environmental stress conditions. This study evaluated the growth performance of Aspergillus section Flavi and Aspergillus niger aggregate strains on Czapek Dox media supplied with a commercial glyphosate formulation as sole source of carbon (CZC), phosphorus (CZP) or nitrogen (CZN). Six Aspergillus spp. strains were evaluated. Each medium was stab-inoculated with fungal spores from 7-day old cultures. Two measures of colony radii were taken daily. All of the Aspergillus section Flavi strains showed a significant increase (from 24 to 44%) in growth rate on the CZN medium, as compared to controls. The A. niger aggregate strains exhibited the same behavioral pattern under all the conditions tested, except on the CZN medium. Velutinous or slightly floccose colonies with abundant sporulation were observed on CZP. Moreover, the colonies produced sparse sporulation on CZC or CZN media, being their appearances completely different from those on the CZP medium. This study establishes that A. section Flavi and A. niger aggregate strains can grow in vitro in the presence of glyphosate, especially when it is used as a sole source of phosphorus or nitrogen.

Fusarium Toxins in Cereals: Occurrence, Legislation, Factors Promoting the Appearance and Their Management

Fusarium diseases of small grain cereals and maize cause significant yield losses worldwide. Fusarium infections result in reduced grain yield and contamination with mycotoxins, some of which have a notable impact on human and animal health. Regulations on maximum limits have been established in various countries to protect consumers from the harmful effects of these mycotoxins. Several factors are involved in Fusarium disease and mycotoxin occurrence and among them environmental factors and the agronomic practices have been shown to deeply affect mycotoxin contamination in the field. In the present review particular emphasis will be placed on how environmental conditions and stress factors for the crops can affect Fusarium infection and mycotoxin production, with the aim to provide useful knowledge to develop strategies to prevent mycotoxin accumulation in cereals.

Isolation of culturable mycobiota from agricultural soils and determination of tolerance to glyphosate of nontoxigenic Aspergillus section Flavi strains

Glyphosate-based herbicides are extensively used in Argentina's agricultural system to control undesirable weeds. This study was conducted to evaluate the culturable mycobiota [colony forming units (CFU) g(-1) and frequency of fungal genera or species] from an agricultural field exposed to pesticides. In addition, we evaluated the tolerance of A. oryzae and nontoxigenic A. flavus strains to high concentrations (100 to 500 mM - 17,000 to 84,500 ppm) of a glyphosate commercial formulation. The analysis of the mycobiota showed that the frequency of the main fungal genera varied according to the analyzed sampling period. Aspergillus spp. or Aspergillus section Flavi strains were isolated from 20 to 100% of the soil samples. Sterilia spp. were also observed throughout the sampling (50 to 100%). Aspergillus section Flavi tolerance assays showed that all of the tested strains were able to develop at the highest glyphosate concentration tested regardless of the water availability conditions. In general, significant reductions in growth rates were observed with increasing concentrations of the herbicide. However, a complete inhibition of fungal growth was not observed with the concentrations assayed. This study contributes to the knowledge of culturable mycobiota from agricultural soils exposed to pesticides and provides evidence on the effective growth ability of A. oryzae and nontoxigenic A. flavus strains exposed to high glyphosate concentrations in vitro.

Possible effects of glyphosate on Mucorales abundance in the rumen of dairy cows in Germany

Glyphosate (N-phosphonomethyl glycine) is registered as a herbicide for many food and non-food crops, as well as non-crop areas where total vegetation control is desired. Glyphosate influences the soil mycobiota; however, the possible effect of glyphosate residues in animal feed (soybean, corn, etc.) on animal mycobiota is almost unknown. Accordingly, the present study was initiated to investigate the mycological characteristics of dairy cows in relationship to glyphosate concentrations in urine. A total of 258 dairy cows on 14 dairy farms in Germany were examined. Glyphosate was detected in urine using ELISA. The fungal profile was analyzed in rumen fluid samples using conventional microbiological culture techniques and differentiated by MALDI-TOF mass spectrometry. LPS-binding protein (LBP) and antibodies (IgG1, IgG2, IgA, and IgM) against fungi were determined in blood using ELISA. Different populations of Lichtheimia corymbifera, Lichtheimia ramosa, Mucor, and Rhizopus were detected. L. corymbifera and L. ramosa were significantly more abundant in animals containing high glyphosate (>40 ng/ml) concentrations in urine. There were no significant changes in IgG1 and IgG2 antibodies toward isolated fungi that were related to glyphosate concentration in urine; however, IgA antibodies against L. corymbifera and L. ramosa were significantly lower in the higher glyphosate groups. Moreover, a negative correlation between IgM antibodies against L. corymbifera, L. ramosa, and Rhizopus relative to glyphosate concentration in urine was observed. LBP also was significantly decreased in animals with higher concentrations of glyphosate in their urine. In conclusion, glyphosate appears to modulate the fungal community. The reduction of IgM antibodies and LBP indicates an influence on the innate immune system of animals.

Survey of Aspergillus section Flavi presence in agricultural soils and effect of glyphosate on nontoxigenic A. flavus growth on soil-based medium

AIMS

To evaluate the cultivable mycobiota from agricultural soils exposed to pesticides, the aflatoxigenic capacity of Aspergillus section Flavi strains and the effect of glyphosate on lag phase and growth rates of native nontoxigenic Aspergillus flavus under different water potential (MPa) conditions on soil-based medium.

METHODS AND RESULTS

Culturable mycobiota analysis from different agricultural soils was performed by the surface spread method. The effect of glyphosate (0-20 mmol l(-1)) on the growth of A. flavus strains was evaluated on a soil extract solid medium. Mycobiota analysis of crop soils showed the presence of twenty-one genera of filamentous fungi. Aspergillus flavus and Aspergillus niger aggregate strains were isolated from the three soil types. Ninety-two per cent of A. flavus strains were toxigenic. In vitro assay results showed that at -0·70 MPa, a significant increase in growth rate in all strains was recorded at 5 and 20 mmol l(-1) of glyphosate. At -2·78 MPa, this parameter remained constant at all glyphosate concentrations, except in GM4 strain where an increase in growth rate was recorded with increasing pesticide concentrations. At -7·06 MPa, a significant increase in growth rate has also been observed in GM 3 strain with 5 mmol l(-1) and in GM 4 strain with 10 and 20 mmol l(-1).

CONCLUSIONS

This study showed that the imperfecti fungi Aspergillus spp., Penicillium spp., Trichoderma spp., Cladosporium spp. and Paecilomyces spp. are isolated as prevalent groups in agricultural soil exposed to pesticides, and the capacity of nontoxigenic A. flavus strains to tolerate different glyphosate concentrations under different water potential (MPa) conditions.

SIGNIFICANCE AND IMPACT OF THE STUDY

This manuscript makes a contribution to the knowledge of cultivable fungal populations from agricultural soils exposed to pesticides and the glyphosate tolerance of A. flavus strains.

Influence of the pesticides glyphosate, chlorpyrifos and atrazine on growth parameters of nonochratoxigenic Aspergillus section Nigri strains isolated from agricultural soils

This investigation was undertake to determine the effect of glyphosate, chlorpyrifos and atrazine on the lag phase and growth rate of nonochratoxigenic A. niger aggregate strains growing on soil extract medium at -0.70, -2.78 and -7.06 MPa. Under certain conditions, the glyphosate concentrations used significantly increased micelial growth as compared to control. An increase of about 30% was observed for strain AN 251 using 5 and 20 mg L(-1) of glyphosate at -2.78 MPa. The strains behaved differently in the presence of the insecticide chlorpyrifos. A significant decrease in growth rate, compared to control, was observed for all strains except AN 251 at -2.78 MPa with 5 mg L(-1). This strain showed a significant increase in growth rate. With regard to atrazine, significant differences were observed only under some conditions compared to control. An increase in growth rate was observed for strain AN 251 at -2.78 MPa with 5 and 10 mg L(-1) of atrazine. By comparison, a reduction of 25% in growth rate was observed at -7.06 MPa and higher atrazine concentrations. This study shows that glyphosate, chlorpyrifos and atrazine affect the growth parameters of nonochratoxigenic A. niger aggregate strains under in vitro conditions.

Influence of herbicide glyphosate on growth and aflatoxin B1 production by Aspergillus section Flavi strains isolated from soil on in vitro assay

The effect of six glyphosate concentrations on growth rate and aflatoxin B1 (AFB1) production by Aspergillus section Flavi strains under different water activity (aW) on maize-based medium was investigated. In general, the lag phase decreased as glyphosate concentration increased and all the strains showed the same behavior at the different conditions tested. The glyphosate increased significantly the growth of all Aspergillus section Flavi strains in different percentages with respect to control depending on pesticide concentration. At 5.0 and 10 mM this fact was more evident; however significant differences between both concentrations were not observed in most strains. Aflatoxin B1 production did not show noticeable differences among different pesticide concentrations assayed at all aW in both strains. This study has shown that these Aspergillus flavus and A. parasiticus strains are able to grow effectively and produce aflatoxins in high nutrient status media over a range of glyphosate concentrations under different water activity conditions.