Growth of spoilage mould and aflatoxin B1 production in naturally contaminated or artificially inoculated maize as influenced by moisture content under ambient tropical condition

Maize (cv. TSZB) samples were re-moistened to different moisture contents (m.c.s) of 13, 15, 17, 20, 25, 30 or 35% and stored with the natural microflora or sterilized before artificial inoculation with either single or mixed moulds (Aspergillus flavus, A. niger, Penicilium purpurogenum and Fusarium moniliforme) and evaluated for initiation time for moulding, fungal populations and aflatoxin B₁ production. Whereas the fungal populations of naturally contaminated maize of 13% m.c. decreased significantly with storage, 17 and 20% m.c. maize increased with the latter showing maximum of about log₁₀ 7 colony forming units (cfu g⁻¹). Of the samples (13, 15, 17 or 20% m.c. maize), only those of ≥20% m.c. showed hazardous levels (>20 ppb) of aflatoxin B₁ production. The 20% m.c. sample also showed a significant positive correlation (r = 0.92) between m.c. and fungal load but those of lower m.c.s exhibited poor correlations, probably reflecting the absence of changes in the m.c.s of the 13, 15 and 17% m.c. maize. Aflatoxin B₁ content of 25% m.c. maize increased with increase in inoculum concentration of A. flavus. Mixed mould inoculation of maize samples resulted in a reduction in aflatoxin concentration with co-cultures of A. flavus and P. purpurogenum showing the lowest production, while that inoculated with A. flavus alone (control) exhibiting the maximum production. Initiation time for moulding was most rapid in ≥20% m.c. maize irrespective of inoculum type, with A. flavus being the most invasive in singly inoculated samples. However, A flavus was most competitive in 20–30% m.c. maize inoculated with mixed moulds, while F. moniliformewas most competitive in the 35% m.c. maize.     

Changes in moisture content,mycoflora and aflatoxin content of rice bran during storage

The changes in moisture content, storage mycoflora and aflatoxin B₁ (AFB₁) in bran from untreated or raw rice (Rr) and parboiled rice (Pbr) stored in small lots in polyethylene bags were studied at 15-day intervals up to 60 days, using five lots of each type of bran. Deterioration was more rapid with reference to all the three parameters, in Rr bran compared to Pbr bran, the former becoming completely overgrown and caked with fungi by the end of 60 days.Aspergillus flavus was the dominant fungus in Pbr bran, whereasA. candidus andTrichoderma viride were abundant in Rr bran. The frequency of incidence as well as concentration of AFB₁ increased with storage time in both types of bran, but the rate of increase as well as overall concentration were much higher in Rr bran. Thus raw rice bran is unsuitable for prolonged storage.Abbreviations AFB₁ aflatoxin B₁ - MC moisture content - Pbr parboiled rice - Rr raw rice     

Examination of fungal growth and aflatoxin production on marihuana

Under favorable growth conditions,Aspergillus flavus andA. parasiticus produced aflatoxins on marihuana. Cultures ofA. flavus ATCC 15548 produced both aflat oxin B₁(AFB₁) and G₁(AFG₁). The production of AFG₁ was substantially greater than that of AFB₁. Cultures ofA. flavus NRRL 3251 andA. parasiticus NRRL 2999 produced only AFB₁. All natural flora cultures tested negative for aflatoxins. NoAspergilli sporulations were observed in these cultures. In the cultures inoculated with known toxigenic fungi, the highest mean level for total aflatoxins was 8.7 g/g of medium. Marihuana appears not to yield large quantities of these mycotoxins but sufficient levels are present to be a potential health hazard for both the user and the forensic analyst who is in daily contact with such plant material. Careful processing, storage, and sanitation procedures should be maintained with marihuana. If these conditions are disregarded due to the illicit status of marihuana, the potential for mycotoxin contamination must be considered.     

Comparative studies on the changes of total soluble proteins and protease activity in Georgian commercial peanuts contaminated by Aspergillus flavus

The presence of Aspergillus species is an indicator of storage conditions, which also suggests the possibility of several biochemical changes in grains. A comparative change in total soluble proteins and protease activity was determined in commercial peanut seeds collected from Georgia State. Protein contents of healthy peanuts, naturally contaminated peanuts and then artificially inoculated peanut seeds with A. flavus were estimated by Bradford method, and protease activity was also determined by using the Protease Detection Kits. Protein contents and the protease activity of the peanuts varied from sample to sample. The soluble protein content of seeds was significantly higher in healthy peanuts than in artificially inoculated or naturally infected peanuts with A. flavus. Protease activity was found to be higher in artificially inoculated seeds than in either naturally infected or healthy peanuts. Level of soluble proteins in buffer extracts of contaminated seeds decreased with incubation time, and protease activity increased with incubation time. These changes may be attributed to host response due to infection, contribution by A. flavus or due to biochemical alterations that occur naturally during the transition from endosperm to seedling during incubation period.     

Impact of a Streptomyces (AS1) strain and its metabolites on control of Aspergillus flavus and aflatoxin B1 contamination in vitro and in stored peanuts

Six actinomycetes were isolated from peanuts in Egypt. Of these, a Streptomyces strain (AS1) was found in in vitro assays to inhibit directly or via secondary metabolites both germination and growth of Aspergillus flavus. Tests of the AS1 cells for direct control of A. flavus populations or aflatoxin B₁ (AFB₁) production on stored peanuts was unsuccessful over 14-day storage periods. However, crude extracts of AS1 metabolites at 50 and 100 ppm completely inhibited spore germination of conidia of A. flavus in vitro over 48 h. Comparison of solvents for extracting the metabolites showed that the ethyl acetate extract was most effective. This gave greater than 85% inhibition of mycelial growth at these concentrations at different water availabilities (water activity; a _w; 0.95, 0.92, and 0.89) and 25°C. Doses of 50, 200, and 500 ppm of AS1 metabolites significantly inhibited populations of A. flavus on stored peanuts at two water stress levels (0.90, 0.93 a _w) at 25°C over 14-day storage periods. The amounts of AFB₁ produced by A. flavus on peanuts stored at 0.90 a _w were significantly decreased by AS1 metabolites for only 7 days. However, at 0.93 a _w doses of 200 and 500 ppm significantly controlled AFB₁ accumulation in peanuts for 14 days.     

Effect of parboiling and bran removal on aflatoxin levels in Sri Lankan rice

Commercial parboiling of rice in Sri Lanka and many south Asian countries provides ideal conditions for the occurrence of aflatoxins because the rice is steeped (allowing fermentation) thus providing ideal conditions for growth of toxigenic Aspergillus species. However the traditional cottage method of parboiling rice, which does not involve steeping, appears to reduce Aspergillus growth even after long storage periods. Preferential infection of parboiled rice by Aspergillus flavus was observed. Aflatoxin contents in inoculated rice produced by commercial parboiling (AFB₁ 60–92 mg/kg) were significantly higher than that in inoculated cottage processed rice (AFB₁ 12–29 g/kg). The steeping (precooking/ soaking) process in commercial parboiling appears to increase the susceptibility of rice grains to fungal infection. Aflatoxin content in grains increased considerably with the increase in duration of soaking. However, the addition of 10 ppm calcium hypochlorite (bleach) to soaking water appreciably reduced A. flavus contamination and subsequent aflatoxin content in parboiled rice. No significant reduction in aflatoxin levels were observed after bran removal of contaminated rice.     

Inhibition of Aspergillus flavus growth and detoxification of aflatoxin B1 by the medicinal plant zimmu (Allium sativum L. × Allium cepa L.)

Aflatoxins are carcinogenic, teratogenic and immunosuppressive secondary metabolites produced by Aspergillus flavus and Aspergillus parasiticus. Aflatoxin contamination of peanut is one of the most important constraints to peanut production worldwide. In order to develop an eco-friendly method of prevention of A. flavus infection and aflatoxin contamination in peanut, aqueous extracts obtained from leaves of 30 medicinal plants belonging to different families were evaluated for their ability to inhibit the growth of A. flavus in vitro. Among them the leaf extract of zimmu (Allium sativum L. × Allium cepa L.) was the only one that showed antifungal activity against A. flavus and recorded 73% inhibition of A. flavus growth. The antifungal activity of the zimmu extract was significantly decreased upon dialysis with a dialysis membrane having molecular cut off 12 kDa or autoclaving at 121°C for 20 min or boiling at 100°C for 10 min and recorded inhibition of 52, 16 and 21%, respectively. When A. flavus was grown in medium containing zimmu extract the production of aflatoxin B₁ (AFB₁) was completely inhibited even at a concentration of 0.5%. When AFB₁ was incubated with zimmu extract a complete degradation of AFB₁ was observed 5 days after incubation. When the roots of zimmu were incubated in water containing 70 ng of AFB₁/ml, a reduction (by 58.5%) in AFB₁ concentration was observed 5 days after incubation. A significant reduction in the population of A. flavus in the soil, kernel infection by A. flavus and aflatoxin contamination in kernels was observed when peanut was intercropped with zimmu. The population of the fungal antagonist, Trichoderma viride in the zimmu-intercropped field increased approximately twofold.     

Aflatoxin accumulation in preharvest maize kernels: Interaction of three fungal species,european corn borer and two hybrids

Summary The interaction was studied among: 1) developing maize kernels (Zea mays L.); 2) European Corn Borer (ECB) (Ostrinia nubilalis Hubner); 3) and three fungal species,Aspergillus flavus Lk. ex Fr.,Penicillium oxalcium Currie and Thom, andFusarium moniliforme Sheld. Two hybrids with varying degrees of resistance to ECB stalk damage were grown in Iowa, Georgia, and Missouri in 1980. One-half of the plots were hand-infested with ECB egg masses. Fungal spores of individual isolates or combinations of the three species were introduced into the silk channels of developing ears in designated plots. ECB larvae were subsequently collected from developing ears. A higher incidence ofA. flavus group isolates was observed in ECB larvae collected from ears that had been inoculated withA. flavus than from insects collected from control ears. Although the resistant hybrid exhibited reduced ECB stalk damage compared with the susceptible variety, no consistent pattern of hybrid effect on the association betweenA. flavus and ECB was observed at all three locations. Differences in aflatoxin B₁ levels in mature kernels from the three locations ranged from 8 ppb in Iowa samples to 419 ppb in Missouri kernels. Conditions during crop development at the Missouri location were particularly conducive to elevated presence ofA. flavus propagules in ECB larvae, increased ECB-mediated stalk damage, and greater toxin concentration in mature kernels.     

Potential for aflatoxin B1 and B2 production by Aspergillus flavus strains isolated from rice samples

In this study, we investigated the potential for aflatoxin B₁ (AFB₁) and B₂ (AFB₂) production in rice grain by 127 strains of Aspergillus flavus isolated from rice grains collected from China. These strains were inoculated onto rice grains and incubated at 28 °C for 21 days. AFB₁ and AFB₂ were extracted and quantified by high-performance liquid chromatography coupled with fluorescence detection. Among the tested strains, 37% produced AFB₁ and AFB₂ with levels ranging from 175 to 124 101 μg kg⁻¹ for AFB₁ and from not detected to 10 329 μg kg⁻¹ for AFB₂. The mean yields of these isolates were 5884 μg kg⁻¹ for AFB₁ and 1968 μg kg⁻¹ for AFB₂. Overall, most of the aflatoxigenic strains produced higher levels of AFB₁ than AFB₂ in rice. The obtained information is useful for assessing the risk of aflatoxin contamination in rice samples.     

Occurrence of aflatoxins and its management in diverse cropping systems of central Tanzania

The staple crops, maize, sorghum, bambara nut, groundnut, and sunflower common in semi-arid agro-pastoral farming systems of central Tanzania are prone to aflatoxin contamination. Consumption of such crop produce, contaminated with high levels of aflatoxin B₁ (AFB₁), affects growth and health. In this paper, aflatoxin contamination in freshly harvested and stored crop produce from central Tanzania was examined, including the efficacy of aflatoxin mitigation technologies on grain/kernal quality. A total of 312 farmers were recruited, trained on aflatoxin mitigation technologies, and allowed to deploy the technologies for 2 years. After 2 years, 188 of the 312 farmers were tracked to determine whether they had adopted and complied with the mitigation practices. Aflatoxigenic Aspergillus flavus and aflatoxin B1 contamination in freshly harvested and stored grains/kernels were assessed. A. flavus frequency and aflatoxin production by fungi were assayed by examining culture characteristics and thin-layer chromatography respectively. AFB₁ was assayed by enzyme-linked immunosorbent assay. The average aflatoxin contamination in freshly harvested samples was 18.8 μg/kg, which is above the acceptable standard of 10 μg/kg. Contamination increased during storage to an average of 57.2 μg/kg, indicating a high exposure risk. Grains and oilseeds from maize, sorghum, and sunflower produced in aboveground reproductive structures had relatively low aflatoxin contamination compared to those produced in geocarpic structures of groundnut and bambara nut. Farmers who adopted recommended post-harvest management practices had considerably lower aflatoxin contamination in their stored kernels/grains. Furthermore, the effects of these factors were quantified by multivariate statistical analyses. Training and behavioral changes by farmers in their post-harvest practice minimize aflatoxin contamination and improve food safety. Moreover, if non-trained farmers receive mitigation training, aflatoxin concentration is predicted to decrease by 28.9 μg/kg on average.     

Evaluation of aflatoxin B1 and ochratoxin A in interacting mixed cultures of Aspergillus sections Flavi and Nigri on peanut grains

The influence of inoculum size on the colony-forming units, production of aflatoxin B₁ (AFB₁) and ochratoxin A (OTA) was determined when Aspergillus flavus and A. niger aggregate strains were cultured alone and in pairs on irradiated peanut grains at 28°C and 0.97 water activity (a_W). The results showed a marked influence of inoculum factor on fungal counts, AFB₁ and OTA production in single and paired cultures. Fungal counts of the A. niger aggregate strain in interacting cultures at 7, 14 and 21?days of incubation were significantly higher than those observed in the A. flavus strain, except in the mixed culture with 10² spores/ml of both strains. In all mixed culture assays, the AFB₁ production was significantly reduced in comparison with the accumulation of mycotoxin in single cultures. A total inhibition in AFB₁ production was observed in some interactions as 10² spores/ml of A. flavus and 10³ spores/ml of A. niger aggregate strain at 7 and 14?days, among others. With regard to OTA production, a stimulation in the interacting cultures was observed at all inoculum sizes and incubation period. The highest levels of OTA accumulation were observed at 14?days for all interacting cultures. The maximum level was reach in the culture 10³ spores/ml of A. niger aggregate and 10⁴ spores/ml of A. flavus (p?<?0.001). These results suggest that, under optimal environmental conditions in peanut grains, the interaction between A. flavus and A. niger aggregate strains could result in an inhibition of AFB₁ and in a stimulation of OTA production.     

Isolation of Bacillus spp. from Thai fermented soybean (Thua-nao): screening for aflatoxin B1 and ochratoxin A detoxification

Aims: To study the interaction between Bacillus spp. and contaminating Aspergillus flavus isolated strains from Thai fermented soybean in order to limit aflatoxin production. To study the detoxification of aflatoxin B₁ (AFB₁) and ochratoxin A (OTA) by Bacillus spp. in order to find an efficient strain to remove these toxins. Methods and Results: One A. flavus aflatoxin-producing strain and 23 isolates of Bacillus spp. were isolated from soybean and fresh Thua-nao collected from the north of Thailand. Inhibition studies of A. flavus and A. westerdijkiae NRRL 3174 (reference strain) growth by all isolates of Bacillus spp. were conducted by dual culture technique on agar plates. These isolates were also tested for AFB₁ and OTA detoxification ability on both solid and liquid media. Most of the strains were able to detoxify aflatoxin but only some of them could detoxify OTA. Conclusions: One Bacillus strain was able to inhibit growth of both Aspergillus strains and to remove both mycotoxins (decrease of 74% of AFB₁ and 92·5% of OTA). It was identified by ITS sequencing as Bacillus licheniformis. The OTA decrease was due to degradation in OTα. Another Bacillus strain inhibiting both Aspergillus growth and detoxifying 85% of AFB₁ was identified as B. subtilis. AFB₁ decrease has not been correlated to appearance of a degradation product. Significance and Impact of the Study: The possibility to reduce AFB₁ level by a strain from the natural flora is of great interest for the control of the quality of fermented soybean. Moreover, the same strain could be a source of efficient enzyme for OTA degradation in other food or feeds.     

Microflora and condition of flood-damaged grains in Manitoba,Canada

Microfloral and other changes which occurred in farm-stored grains at, below and above the maximum water level were documented after the Red River Valley flood of spring 1979 in southern Manitoba, Canada. Results of flood-damage simulation studies carried out in the laboratory on wheat, rapeseed and flax generally confirmed those from the field. In laboratory simulation studies with flooded grains in tanks a 2.5–10.0 cm thick crust of sprouted seeds developed just above the maximum water level. Migration of moisture occurred upwards from the base of the crust and maximum temperatures just beneath the crust. Beneath the crust was a horizon of putrid seeds of zero germination, and above the crust a horizon of visible post-harvest molds, e.g.Aspergillus flavus andPenicillium spp. and harvest molds, e.g.Trichothecium roseum. Penicillium verrucosum var.cyclopium occurred throughout the profile, whereasAlternaria alternata, Wallemia sebi andAspergillus glaucus group species were confined to upper horizons because of low seed moisture andA. flavus and A. versicolor to lower horizons of high moisture. Aflatoxins B₁ at 426 ppb and B₂ at 34 ppb were the only mycotoxins detected in either study, and occurred in a partially filled granary of flax which had been affected by flood waters. Pressure effects produced by the expanding seeds such as increase in height of grain mass and splitting of seams of granaries were evident in both studies. Rounded or slippery seeds, e.g. peas, flax, were associated usually with vertical pressure effects whereas irregularly-shaped seeds, e.g. wheat with lateral pressure effects. It is hoped that this work will provide a better understanding of the processes involved when grain is damaged by flood waters and assist in the development of improved salvage procedures.Contribution No. 942, Agriculture Canada Research Station, 195 Dafoe Road, Winnipeg, Manitoba, R3T 2M9.     

Influence of genotype and texture on zein content in endosperm of maize grains

The effect of genotypes and texture on the content of proteins in maize grains was examined by assessing absolute amounts of six protein fractions in the whole endosperms of four wild‐type lines with high protein content and four quality protein maize (QPM) varieties and for hand‐dissected hard and soft endosperm regions from eight other lines. As previously reported for six wild‐type lines and their opaque‐2(o2) versions, zeins were predominant for all genetic backgrounds and all types of endosperms. From these data and others the amounts of zeins and true proteins (crude proteins free of non‐protein nitrogen) in developing and mature endosperms of wild‐type lines were correlated. The data points for zeins from hard endosperms lay between the regression line and the upper limit of confidence area. Those for zeins from soft endosperms were located at the lower part of confidence area and on a level with the points corresponding to the most immature endosperms. Furthermore, some data points for zeins from o2 and QPM samples lay near the lower limit while the others were outside the confidence area. This suggested an initial zein accumulation dependent on the genotype at a low relative rate, followed by an accumulation at higher rate. The conditions used for isolating and quantitating zeins are discussed.     

Mycotoxigenic isolates and toxin production on buckwheat and rice hulls used as bedding materials

Summary A pre-evaluation of the samples of both buckwheat and rice hulls, planned for use as pillow fill-materials, showed the presence ofAspergillus flavus, A glaucus, andPenicillium spp. Buckwheat- and rice-hull media (BHM and RHM) inoculated withA. flavus both supported the production of aflatoxins (AFB₁ and AFG₁) in the parts per million (ppm) range; BHM yielded approximately twice the quantity of both AFB₁ and AFG₁ than did RHM. Both BHM and RHM inoculated withFusarium tricinctum yielded trichothecenes (T-2 toxins) in the ppm range, with the BHM producing approximately three times more T-2 toxins than the RHM. Also,F. tricinctum grown on both media produced several metabolites which included HT-2, 3-OH T-2, neosolariol, T-2 triol, and T-2 tetraol. The BHM yielded all of the above, while the RHM failed to support the production of the 3-OH T-2 toxin. In addition, neither medium inoculated withMyrothecium roridum yielded any detectable levels of macrocyclic trichothecenes. The results indicated that these materials have the potential to become contaminated with mycotoxins.     

A Survey on Distribution of Aspergillus Section Flavi in Corn Field Soils in Iran: Population Patterns Based on Aflatoxins, Cyclopiazonic Acid and Sclerotia Production

Soil isolates of Aspergillus section Flavi from Mazandaran and Semnan provinces with totally different climatic conditions in Iran were examined for aflatoxins (AFs; B and G types), cyclopiazonic acid (CPA) and sclerotia production. A total of 66 Aspergillus flavus group strains were identified from three species viz. Aspergillus flavus, Aspergillus parasiticus and Aspergillus nomius in both locations. A. flavus (87.9%) was found to be the prominent species followed by A. nomius (9.1%) and A. parasiticus (3.0%). Only 27.5% of A. flavus isolates were aflatoxigenic (B₁ or B₁ and B₂), out of which approximately 75% were capable to producing CPA. All the A. parasiticus and A. nomius isolates produced AFs of both B (B₁ and B₂) and G (G₁ and G₂) types, but did not produce CPA. Sclerotia production was observed in only 4 isolates of A. flavus among all 66 isolates from three identified species. A. flavus isolates were classified into various chemotypes based on the ability to produce aflatoxins and CPA. In this study, a new naturally occurring toxigenic A. flavus chemotype comprising of two strains capable of producing more AFB₂ than AFB₁ has been identified. A relatively larger proportion of aflatoxigenic A. flavus strains were isolated from corn field soils of Mazandaran province which indicate a possible relationship between high levels of relative humidity and the incidence of aflatoxin-producing fungi. The importance of incidence of Aspergillus section Flavi in corn field soils regard to their mycotoxin production profiles and crop contamination with special reference to climatic conditions is discussed.     

丁酸梭菌发酵培养基的优化及发酵产物对黄曲霉毒素B1的降解

【背景】丁酸梭菌是专性厌氧的新一代芽孢益生菌,耐热、耐酸、抗逆性强,极具应用价值和开发前景。【目的】优化丁酸梭菌发酵培养基并初步研究其发酵液对黄曲霉菌的抑制作用和降解黄曲霉毒素B₁ (aflatoxin B₁, AFB₁)的能力。【方法】利用响应面法对发酵培养基进行优化,采用牛津杯法对丁酸梭菌发酵液抑制黄曲霉菌生长进行研究,并通过酶联免疫法测定发酵液对AFB₁的降解能力。【结果】优化后的发酵培养基为：葡萄糖18.1g/L,大豆蛋白胨29.7g/L,磷酸氢二钾3.8 g/L,氯化钠2.0 g/L,乙酸钠4.0 g/L,结晶硫酸镁1.2 g/L,L-半胱氨酸盐酸盐0.3 g/L。优化后的丁酸梭菌生物量由8.99×10⁸个/mL提高至2.28×10⁹个/mL,是优化前的2.54倍。丁酸梭菌发酵液对致病真菌黄曲霉菌的抑菌效果十分显著,其上清液经浓缩后对AFB₁降解72h的降解率达到68.65%,初步分析表明上清液中对AFB₁     

An insight into the distribution,genetic diversity,and mycotoxin production of <Emphasis Type="Italic">Aspergillus</Emphasis> section <Emphasis Type="Italic">Flavi</Emphasis> in soils of pistachio orchards

In the present study, 193 Aspergillus strains were isolated from a total of 100 soil samples of pistachio orchards, which all of them were identified as Aspergillus flavus as the most abundant species of Aspergillus section Flavi existing in the environment. Approximately 59%, 81%, and 61% of the isolates were capable of producing aflatoxins (AFs), cyclopiazonic acid (CPA), and sclerotia, respectively. The isolates were classified into four chemotypes (I to IV) based on the ability to produce AFs and CPA. The resulting dendrogram of random amplified polymorphic DNA (RAPD) analysis of 24 selected A. flavus isolates demonstrated the formation of two separate clusters. Cluster 1 contained both aflatoxigenic and non-aflatoxigenic isolates (17 isolates), whereas cluster 2 comprised only aflatoxigenic isolates (7 isolates). All the isolates of cluster 2 produced significantly higher levels of AFs than those of cluster 1 and the isolates that produced both AFB₁ and AFB₂ were found only in cluster 2. RAPD genotyping allowed the differentiation of A. flavus from Aspergillus parasiticus as a closely related species within section Flavi. The present study has provided for the first time the relevant information on distribution and genetic diversity of different A. flavus populations from nontoxigenic to highly toxigenic enable to produce hazardous amounts of AFB₁ and CPA in soils of pistachio orchards. These fungi, either toxigenic or not-toxigenic, should be considered as potential threats for agriculture and public health.     

Comparison of growth and aflatoxin B1 production profiles of Aspergillus flavus strains on conventional and isogenic GM-maize-based nutritional matrices

Maize grown in both North and South America are now predominantly genetically modified (GM) cultivars with some resistance to herbicide, pesticide, or both. There is little information on the relative colonisation and aflatoxin B₁ (AFB₁) production with maize meal-based nutritional matrices based on kernels of non-GM maize and isogenic GM-ones by strains of Aspergillus flavus. The objectives were to examine the effect of interacting conditions of temperature (25–35 °C) and water availability (0.99–0.90 water activity, a_w) on (a) mycelial growth, (b) AFB₁ production and (c) develop contour maps of optimum and marginal conditions of these parameters for four strains of A. flavus on three different non-GM and isogenic GM-maize based nutritional media. The growth of the four strains of A. flavus (three aflatoxigenic; one non-aflatoxigenic) was relatively similar in relation to the temperature × a_w conditions examined on both non-GM and GM-based matrices. Optimum growth overall was at 30–35 °C and 0.99 a_w for all four strains. Under water stress (0.90 a_w) growth was optimum at 35 °C. Statistically: non-GM, GM cultivars, temperature and a_w all significantly affected growth rates. For AFB₁ production, all single and interacting factors were statistically significant except for non-GM × GM cultivar. In conclusion, colonisation of GM- and non-GM nutritional sources was similar for the different A. flavus strains examined. The contour maps will be very useful for understanding the ecological niches for both toxigenic and non-toxigenic strains in the context of the competitive exclusion of those producing aflatoxins.