Fumonisin B1 Production and Growth of Fusarium moniliforme and Fusarium proliferatum on Maize, Wheat, and Barley Grain

Climate Change-A Global Threat Resulting in Increasing Mycotoxin Occurrence

During the last decade, scientists have given increasingly frequent warnings about global warming, linking it to mycotoxin-producing moulds in various geographical regions across the world. In the future, more pronounced climate change could alter host resilience and host-pathogen interaction and have a significant impact on the development of toxicogenic moulds and the production of their secondary metabolites, known as mycotoxins. The current climate attracts attention and calls for novel diagnostic tools and notions about the biological features of agricultural cultivars and toxicogenic moulds. Since European climate environments offer steadily rising opportunities for Aspergillus flavus growth, an increased risk of cereal contamination with highly toxic aflatoxins shall be witnessed in the future. On top of that, the profile (representation) of certain mycotoxigenic Fusarium species is changing ever more substantially, while the rise in frequency of Fusarium graminearum contamination, as a species which is able to produce several toxic mycotoxins, seen in northern and central Europe, is becoming a major concern. In the following paper, a high-quality approach to a preventative strategy is tailored to put a stop to the toxicogenic mould- and mycotoxin-induced contamination of foods and feeds in the foreseeable future.

Environmental Effects of Temperature and Water Potential on Mycelial Growth of Neocosmospora solani and Fusarium spp. Causing Dry Root Rot of Citrus

This study aimed at evaluating the effect of environmental factors temperature and water potential (Ψw) on the growth of Neocosmospora (Fusarium) solani and three Fusarium species (F. oxysporum, F. equiseti and F. brachygibbosum) associated with citrus dry root rot and to determine the optimum and marginal rate for their growth. The effects of incubation temperature (5-40 °C), water potentials (Ψw) (- 15.54; - 0.67 MPa) (0.89-0.995 a_w) and their interaction (5-30 °C) was evaluated on the in vitro radial growth rates of Fusarium spp. and on their lag phase. Secondary models were used to model the combined effect of these factors on radial growth rate. The results underlined a highly significant effects (P < 0.001) of Ψw and temperature and their interactions on radial growth rates and lag phases (λ). The Four studied species were shown tolerant to a temperature of 35 °C with an optimum mycelial growth at 30 for N. solani and F. oxysporum and at 25 °C for F. equiseti and F. brachygibbosum. However, no growth was observed at both temperatures 5 and 40 °C and at Ψw of - 9.68 MPa (0.93 a_w). The optimum water potential for growth was ≥- 2.69 MPA (>0.98 a_w). The results from the polynomial model and response surface showing good agreement between observed and predicted values. The external validation on citrus fruit indicated slight differences between predicted and observed values of radial growth. The results of this study will be beneficial for understanding the ecological knowledge of these species and thereby limited preventively their occurrence.

A Fumonisin Prevention Tool for Targeting and Ranking Agroclimatic Conditions Favoring Exposure in French Maize-Growing Areas

The levels of fumonisins (FUMO)-mycotoxins produced by Fusarium verticillioides-in maize for food and feed are subject to European Union regulations. Compliance with the regulations requires the targeting of, among others, the agroclimatic factors influencing fungal contamination and FUMO production. Arvalis-Institut du végétal has created a national, multiyear database for maize, based on field survey data collected since 2003. This database contains information about agricultural practices, climatic conditions and FUMO concentrations at harvest for 738 maize fields distributed throughout French maize-growing regions. A linear mixed model approach highlights the presence of borers and the use of a late variety, high temperatures in July and October, and a water deficit during the maize cycle as creating conditions favoring maize contamination with Fusarium verticillioides. It is thus possible to target a combination of risk factors, consisting of this climatic sequence associated with agricultural practices of interest. The effects of the various possible agroclimatic combinations can be compared, grouped and classified as promoting very low to high FUMO concentrations, possibly exceeding the regulatory threshold. These findings should facilitate the creation of a national, informative and easy-to-use prevention tool for producers and agricultural cooperatives to manage the sanitary quality of their harvest.

Discovery and Development of Novel Anti-fungal Peptides Against Foodspoiling Fungi

BACKGROUND

Despite the extensive research carried out to develop natural antifungal preservatives for food applications, there are very limited antifungal agents available to inhibit the growth of spoilage fungi in processed foods. Scope and Approach: Therefore, this review summarizes the discovery and development of antifungal peptides using lactic acid bacteria fermentation to prevent food spoilage by fungi. The focus of this review will be on the identification of antifungal peptides, potential sources, the possible modes of action and properties of peptides considered to inhibit the growth of spoilage fungi. Key Findings and Conclusions: Antifungal peptides generated by certain lactic acid bacteria strains have a high potential for applications in a broad range of foods. The mechanism of peptides antifungal activity is related to their properties such as low molecular weight, concentration and secondary structure. The antifungal peptides were proposed to be used as bio-preservatives to reduce and/or replace chemical preservatives.

Antifungal Activity of Eclipta alba Metabolites against Sorghum Pathogens

Unscientific use of synthetic fungicides in plant disease management has environmental ramifications, such as disease resurgence and serious health problems due to their carcinogenicity. This has prompted the identification and development of eco-friendly greener alternatives. Eclipta alba extract was evaluated for its antifungal activity in in vitro and in vivo against sorghum fungal pathogens Fusarium thapsinum, Alternaria alternata, Epicoccum sorghinum, and Curvularia lunata. The column purified methanolic extract of E. alba exhibited good antifungal activity against the target pathogens. The MIC was observed at 80 mg/mL for all tested pathogenic fungi, whereas MFC was 80 mg/mL for E. sorghinum, 100 mg/mL for F. thapsinum, A. alternata, and C. lunata. In vitro germination percentage was significantly high in seeds treated with E. alba extract (98%) over untreated control (91%). Significant disease protection of 95% was observed in greenhouse and 66% disease protection was noticed in field experiments. The efficacy of E. alba extract in field conditions was improved with the use of E. alba extract formulation. The profile of phytochemicals in E. alba methanol fractions was obtained by ultra-performance liquid chromatography (UPLC) mass spectroscopy. The [M-H]⁻ at m/z 313.3, m/z 797.9, and m/z 269.0 revealed the presence of wedelolactone, eclalbasaponin II, and apigenin, respectively. The H-nuclear magnetic resonance spectroscopy (¹H-NMR) chemical shift value supported the findings of the mass spectrometry. The results highlighted the possible use of E. alba methanolic extract as alternative to chemical fungicide in sorghum disease management.

The Major Fusarium Species Causing Maize Ear and Kernel Rot and Their Toxigenicity in Chongqing, China

Fusarium verticillioides, F. proliferatum, and F. meridionale were identified as the predominant fungi among 116 Fusarium isolates causing maize ear and kernel rot, a destructive disease in Chongqing areas, China. The toxigenic capability and genotype were determined by molecular amplification and toxin assay. The results showed that the key toxigenic gene FUM1 was detected in 47 F. verticillioides and 19 F. proliferatum isolates. Among these, F. verticillioides and F. proliferatum isolates mainly produced fumonisin B₁, ranging from 3.17 to 1566.44, and 97.74 to 11,100.99 µg/g for each gram of dry hyphal weight, with the averages of 263.94 and 3632.88 µg/g, respectively, indicating the F. proliferatum isolates on average produced about an order of magnitude more fumonisins than F. verticillioides did in these areas, in vitro. Only NIV genotype was detected among 16 F. meridionale and three F. asiaticum isolates. Among these, 11 F. meridionale isolates produced NIV, varying from 17.40 to 2597.34 µg/g. ZEA and DON toxins were detected in 11 and 4 F. meridionale isolates, with the toxin production range of 8.35-78.57 and 3.38-33.41 µg/g, respectively. Three F. asiaticum isolates produced almost no mycotoxins, except that one isolate produced a small amount of DON. The findings provide us with insight into the risk of the main pathogenic Fusarium species and a guide for resistance breeding in these areas.

Influence of water activity and temperature on growth and fumonisin production by Fusarium proliferatum strains on irradiated wheat grains

Wheat is the most important cereal consumed by the Argentine population. In previous studies performed in durum and common wheat grains in this country it has been observed fumonisin contamination as well as high incidence of Fusarium proliferatum. Fumonisins are toxic fungal metabolites, and consumption of fumonisin-contaminated maize has been epidemiologically associated with oesophageal cancer and neural tube defects in some human populations. Using irradiated wheat-grains, the effects of abiotic factors, temperature (15, 25, and 30°C) and water activity (a_W; 0.995, 0.98, 0.96, 0.94, 0.92, and 0.88), on mycelial growth and fumonisin biosynthesis were compared for three F. proliferatum strains isolated from wheat grains in Argentina. Although all isolates showed similar profiles of growth, the fumonisin production profiles were slightly different. Maximum growth rates were obtained at the highest a_W (0.995) and 25°C, with growth decreasing as the a_W of the medium was reduced. Maximum amounts of total fumonisins (FB₁, FB₂ and FB₃) were produced at 0.995 a_W and 15°C for 2 strains, and at 25°C and 0.995 a_W for the third one. Fumonisins concentrations varied considerably depending on the a_W and temperature interactions assayed. Studied strains showed different fumonisin production profiles. Two-dimensional profiles of a_W by temperature interactions were developed from these data to identify areas where conditions indicate a significant risk of fumonisins accumulation on wheat. As a result, temperature and a_W conditions that resulted in fumonisins production are those found during wheat grain development (especially milk and dough stages) in the field. This is the first study made using irradiated wheat grains and provides useful baseline data on conditions representing a low or a high risk for fumonisins contamination of wheat grains which is of concern because this cereal is destined mainly for human consumption.

A study on the physicochemical parameters for Penicillium expansum growth and patulin production: effect of temperature, pH, and water activity

Penicillium expansum is among the most ubiquitous fungi disseminated worldwide, that could threaten the fruit sector by secreting patulin, a toxic secondary metabolite. Nevertheless, we lack sufficient data regarding the growth and the toxigenesis conditions of this species. This work enables a clear differentiation between the favorable conditions to the P. expansum growth and those promising for patulin production. A mathematical model allowing the estimation of the P. expansum growth rate according to temperature, a W, and pH, was also developed. An optimal growth rate of 0.92 cm/day was predicted at 24°C with pH level of 5.1 and high a W level of 0.99. The model's predictive capability was tested successfully on artificial contaminated apples. This model could be exploited by apple growers and the industrialists of fruit juices in order to predict the development of P. expansum during storage and apple processing.

Inhibitory mechanism of butylated hydroxyanisole against infection of Fusarium proliferatum based on comparative proteomic analysis

Fusarium proliferatum as a filamentous fungal pathogen can produce mycotoxins that can contaminate postharvest fruits and thus impact risks on human health. The extracellular proteomes of F. proliferatum grown in the absence and presence of butylated hydroxyanisole (BHA) were analyzed comparatively. A total of 66 significantly different expressed secreted proteins were identified by LC-ESI-MS/MS analysis. The BHA treatment suppressed the accumulation of some pathogenic factors such as aspartic protease, cell wall degradation enzymes, porin, superoxide dismutase and glyceraldehyde-3-phosphate dehydrogenase. On the contrary, the BHA treatment increased the abundances of some proteins, such as ATP binding cassette transporter substrate-binding protein and lipopolysaccharide-assembly lipoprotein, involved in the growth of F. proliferatum. These findings suggest that BHA treatment could influence the pathogenic ability of F. proliferatum via inhibiting the levels of virulence factors and cell wall degradation-associated enzymes. Moreover, the induction of the growth-related proteins after the BHA treatment suggests that the livelihood of F. proliferatum might depend on the cost of reduced pathogenic ability. This study has provided some evidence for understanding the complicated mechanisms of F. proliferatum infection in an effort to develop new targets for the control of this fungal pathogen.

BIOLOGICAL SIGNIFICANCE

To better understand the inhibitory mechanism of F. proliferatum by butylated hydroxyanisole (BHA) treatment, a comprehensive proteomic analysis of the secreted proteins of F. proliferatum was firstly conducted. Among the 66 identified spots, 34 and 32 proteins were down- and up-accumulated significantly by BHA treatment, respectively. Many of the identified key protein species were involved in the pathogenic ability and the growth of F. proliferatum. This study is helpful for broadening our knowledge of the pathogenic mechanism of F. proliferatum.

Ecophysiology of Fusarium temperatum isolated from maize in Argentina

The effect of water activity (aw = 0.95, 0.98 and 0.995), temperature (15, 25 and 30°C), incubation time (7, 14, 21 and 28 days), and their interactions on growth and moniliformin (MON), beauvericin (BEA), fusaproliferin (FUS) and fumonisin B1 (FB1) production by two strains of Fusarium temperatum isolated from Argentinean maize were determined in vitro on sterile layers of maize grains. The results showed that there was a wide range of conditions for growth and mycotoxins production by F. temperatum. Both strains were found to grow faster with increasing aw and at 30°C. In relation to mycotoxin production, the two strains produced more FUS than the other mycotoxins regardless of aw or temperature evaluated (maximum = 50,000 μg g(-1)). For FUS, MON and BEA, the maximum levels were observed at 0.98 aw and 30°C (50,000, 5000 and 2000 μg g(-1) respectively). The lowest levels for these three mycotoxins were detected at 15°C and 0.95 aw (1700 and 100 μg g(-1) for FUS and MON respectively), and at 0.98 aw (400 μg g(-1) for BEA). The maximum levels of FB1 were produced at 15°C and 0.98 aw (1000 μg g(-1)). At all aw and temperatures combinations evaluated there was an increase in toxin concentrations with time incubation. The maximum levels were detected at 21 days. Statistical analyses of aw, temperature, incubation time, and the two- and three-way interactions between them showed significant effects on mycotoxins production by F. temperatum. For its versatility on growth and mycotoxin production, F. temperatum represents a toxicological risk for maize in the field and also during grain storage.

Effect of temperature and water activity on gene expression and aflatoxin biosynthesis in Aspergillus flavus on almond medium

Almonds are among the commodities at risk of aflatoxin contamination by Aspergillus flavus. Temperature and water activity are the two key determinants in pre and post-harvest environments influencing both the rate of fungal spoilage and aflatoxin production. Varying the combination of these parameters can completely inhibit or fully activate the biosynthesis of aflatoxin, so it is fundamental to know which combinations can control or be conducive to aflatoxin contamination. Little information is available about the influence of these parameters on aflatoxin production on almonds. The objective of this study was to determine the influence of different combinations of temperature (20 °C, 28 °C, and 37 °C) and water activity (0.90, 0.93, 0.96, 0.99 aw) on growth, aflatoxin B1 (AFB1) production and expression of the two regulatory genes, aflR and aflS, and two structural genes, aflD and aflO, of the aflatoxin biosynthetic cluster in A. flavus grown on an almond medium solidified with agar. Maximum accumulation of fungal biomass and AFB1 production was obtained at 28 °C and 0.96 aw; no fungal growth and AFB1 production were observed at 20 °C at the driest tested conditions (0.90 and 0.93 aw). At 20° and 37 °C AFB1 production was 70-90% lower or completely suppressed, depending on aw. Reverse transcriptase quantitative PCR showed that the two regulatory genes (aflR and aflS) were highly expressed at maximum (28 °C) and minimum (20 °C and 37 °C) AFB1 production. Conversely the two structural genes (aflD and aflO) were highly expressed only at maximum AFB1 production (28 °C and 0.96-0.99 aw). It seems that temperature acts as a key factor influencing aflatoxin production which is strictly correlated to the induction of expression of structural biosynthesis genes (aflD and aflO), but not to that of aflatoxin regulatory genes (aflR and aflS), whose functional products are most likely subordinated to other regulatory processes acting at post-translational level. The results of this study are useful to select conditions that could be used in the almond processing chain to suppress aflatoxin production in this important product.

Two-dimensional environmental profiles of growth and fumonisin production by Fusarium proliferatum on a wheat-based substrate

The effect of water activity (aW; 0.995, 0.99, 0.98, 0.96, 0.94, 0.92, and 0.90), temperature (15, 25, and 30°C), incubation time (7, 14, 21 and 28days), and their interactions on mycelial growth and fumonisin production on wheat-based medium by three Fusarium proliferatum strains isolated from wheat in Argentina was evaluated. Maximum growth rates were obtained at the highest aW (0.995) and 30°C, with growth decreasing as the aW of the medium was reduced. Maximum amounts of total fumonisins (FB1, FB2 and FB3) were produced at 0.99 aW and 25°C after 21 and 28days of incubation for 2 strains, and at 15°C and 0.98 aW after 28days of incubation for the third strain. The fumonisin concentrations varied considerably depending on the aW and temperature interactions assayed. The studied strains had different fumonisin production profiles. F. proliferatum ITEM 15661 and ITEM 15664 produced FB1 and FB2 whereas F. proliferatum ITEM 15654 was able to produce FB1, FB2 and FB3. Interestingly, fumonisin production profiles for each particular strain were related to incubation temperatures. Fumonisins were produced from 15 to 30°C and at aW values of 0.92 to 0.995 after 21 to 28days of incubation. However at 7 and 14days of incubation small amounts of fumonisin were produced at aW lower than 0.94. Two-dimensional profiles of aW by temperature interactions were developed from these data to identify areas where conditions indicate a significant risk from fumonisin accumulation on wheat. Temperature and aW conditions that resulted in fumonisin production are those found during wheat grain development (especially milk and dough stages) in the field. This study provides useful base line data on conditions representing a high and a low risk for contamination of wheat by fumonisins which is becoming of greater concern because this cereal is destined mainly for human consumption.

FUM and BIK gene expression contribute to describe fumonisin and bikaverin synthesis in Fusarium verticillioides

Fusarium verticillioides is a maize pathogen that produces toxic secondary metabolites, including fumonisins and bikaverin. The regulation of biosynthetic gene expression and the production of these metabolites are not fully understood and in this study we investigated the influence of water activity (0.955 and 0.990) on the expression of 5 genes (FUM3-FUM8-FUM13-FUM14 and BIK1) in F. verticillioides strains after 14 and 21days incubation. Fumonisin production and biosynthetic gene expression were greatest at a(w)=0.990, and the same trend was observed for bikaverin production, and BIK1 expression. FUM3 and FUM14 were the most highly expressed genes and were positively correlated with the production of FB(1), FB(2) and FB(3). When FUM14 is more highly expressed than FUM3 the amount of FB(3) quantified is higher with respect to FB(1); this could be explained by the role of FUM3 in the hydroxylation of FB(3) to FB(1).

Co-occurrence of fumonisins and deoxynivalenol in wheat and maize harvested in Serbia

A survey was undertaken to determine total fumonisins (FUMs) and deoxynivalenol (DON) in wheat and maize. Out of 75 wheat samples, 50.7% contained FUMs in the span from 27 to 614 ng/g, while 65.3% contained DON in the span from 64 to 1,604 ng/g. Out of 24 maize samples, contents of FUMs in one and of DON in three samples were above the maximal limit. This is the one of rare reports of the natural co-occurrence of FUMs and DON in wheat and maize, and the first report of their correlation in different wheat cultivars.

Fumonisins B, A and C profile and masking in Fusarium verticillioides strains on fumonisin-inducing and maize-based media

The production of fumonisin B, A and C and hidden and partially hydrolysed fumonisin occurrence was investigated in 3 strains of Fusarium verticillioides isolated from maize, cultured for 21-45days on malt extract medium at 25°C and 0.955-0.990 water activity (a(w)). Fumonisin A-B and C series were produced by all the strains in all conditions studied, with B-fumonisin≫C-fumonisin>A-fumonisin following a similar trend. The dynamic of fumonisin production was significantly influenced by factors considered and their interaction, with a(w)=0.990 as favourable condition in ITEM 10026 and ITEM 10027. All fumonisins were maximised at 30days incubation in ITEM 10027 and ITEM 1744 and at 45days incubation in ITEM 10026. Partially hydrolysed fumonisins were detected only for the B-group. Hidden fumonisins were never observed in Fusarium cultures grown on malt extract medium but were detected in the additional trial on maize-based medium, suggesting that the masking phenomenon can occur only in a complex matrix.

Near-infrared (NIR) hyperspectral imaging and multivariate image analysis to study growth characteristics and differences between species and strains of members of the genus Fusarium

Near-infrared (NIR) hyperspectral imaging was used to study three strains of each of three Fusarium spp. (Fusarium subglutinans, Fusarium proliferatum and Fusarium verticillioides) inoculated on potato dextrose agar in Petri dishes after either 72 or 96 h of incubation. Multivariate image analysis was used for cleaning the images and for making principal component analysis (PCA) score plots and score images and local partial least squares discriminant analysis (PLS-DA) models. The score images, including all strains, showed how different the strains were from each other. Using classification gradients, it was possible to show the change in mycelium growth over time. Loading line plots for principal component (PC) 1 and PC2 explained variation between the different Fusarium spp. as scattering and chemical differences (protein production), respectively. PLS-DA prediction results (including only the most important strain of each species) showed that it was possible to discriminate between species with F. verticillioides the least correctly predicted (between 16 and 47 % pixels correctly predicted). For F. subglutinans, 78-100 % pixels were correctly predicted depending on the training and test sets used. Similarly, the percentage correctly predicted values of F. proliferatum were 60-80 %. Visualisation of the mycelium radial growth in the PCA score images was made possible due to the use of NIR hyperspectral imaging. This is not possible with bulk spectroscopy in the visible or NIR regions.

The dent stage of maize kernels is the most conducive for fumonisin biosynthesis under field conditions

The fungal pathogen Fusarium verticillioides infects maize ears and produces fumonisins, known for their adverse effects on human and animal health. Basic questions remain unanswered regarding the kernel stage(s) associated with fumonisin biosynthesis and the kernel components involved in fumonisin regulation during F. verticillioides-maize interaction under field conditions. In this 2-year field study, the time course of F. verticillioides growth and fumonisin accumulation in developing maize kernels, along with the variations in kernel pH and amylopectin content, were monitored using relevant and accurate analytical tools. In all experiments, the most significant increase in fumonisin accumulation or in fumonisin productivity (i.e., fumonisin production per unit of fungus) was shown to occur within a very short period of time, between 22/32 and 42 days after inoculation and corresponding to the dent stage. This stage was also characterized by acidification in the kernel pH and a maximum level of amylopectin content. Our data clearly support published results based on in vitro experiments suggesting that the physiological stages of the maize kernel play a major role in regulating fumonisin production. Here we have validated this result for in planta and field conditions, and we demonstrate that under such conditions the dent stage is the most conducive for fumonisin accumulation.

Large scale purification of B-type fumonisins using centrifugal partition chromatography (CPC)

For toxicological studies of B-type fumonisin in animals, high amounts of pure fumonisins are needed. In the past, several methods for the isolation and purification of fumonisins have been published, stating the problem of high losses of fumonisins during chromatography on solid phases. In this manuscript we describe a new approach based on liquid-liquid partition techniques using centrifugal partition chromatography in combination with ion exchange chromatography for the large-scale isolation of B-type fumonisins with good recovery rates, minimizing losses of fumonisins during the purification. A batch of cultures grown on solid media of 2 kg maize yields approximately 1 g of pure fumonisins with a purity of >98%.

Modelling the effect of water activity and temperature on growth rate and aflatoxin production by two isolates of Aspergillus flavus on paddy

AIMS

This study was conducted to characterize the growth of and aflatoxin production by Aspergillus flavus on paddy and to develop kinetic models describing the growth rate as a function of water activity (a(w)) and temperature.

METHODS AND RESULTS

The growth of A. flavus on paddy and aflatoxin production were studied following a full factorial design with seven a(w) levels within the range of 0·82-0·99 and seven temperatures between 10 and 43°C. The growth of the fungi, expressed as colony diameter (mm), was measured daily, and the aflatoxins were analysed using HPLC with a fluorescence detector. The maximum colony growth rates of both isolates were estimated by fitting the primary model of Baranyi to growth data. Three potentially suitable secondary models, Rosso, polynomial and Davey, were assessed for their ability to describe the radial growth rate as a function of temperature and a(w). Both strains failed to grow at the marginal temperatures (10 and 43°C), regardless of the a(w) studied, and at the a(w) level of 0·82, regardless of temperature. Despite that the predictions of all studied models showed good agreement with the observed growth rates, Davey model proved to be the best predictor of the experimental data. The cardinal parameters as estimated by Rosso model were comparable to those reported in previous studies. Toxins were detected in the range of 0·86-0·99 a(w) with optimal a(w) of 0·98 and optimal temperature in the range of 25-30°C.

CONCLUSIONS

The influences of a(w) and temperature on the growth of A. flavus and aflatoxin production were successfully characterized, and the models developed were found to be capable of providing good, related estimates of the growth rates.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results of this study could be effectively implemented in minimizing the risk of aflatoxin contamination of the paddy at postharvest.

Field control of Fusarium ear rot, Ostrinia nubilalis (Hübner), and fumonisins in maize kernels

BACKGROUND

A 6 year study was conducted to evaluate the possible support of pesticides in mitigating mycotoxin contamination in maize grown in northern Italy. Different pesticides to control Ostrinia nubilalis (Hübner) (ECB), Fusarium verticillioides (Sacc.) Nirenb. and Aspergillus flavus Link were considered to check their efficacy and the best schedule to reduce fumonisin and aflatoxin contamination.

RESULTS

Fumonisin B1 (FB1) contamination at harvest has been reduced by ECB control, while the addition of ingredients targeted to F. verticillioides gave a limited advantage, mainly with low FB1 contamination; nevertheless, fusaria control is relevant in high-risk conditions, when FB1 is likely to exceed the legal limit. The combination of fungal and pest control in a single spray at silk browning stage (BBCH 67) is the best way of application. These results are robust because they were obtained in a 6 year trial, with relevant differences in meteorological conditions, ECB and fungal presence and mycotoxin contamination.

CONCLUSION

Insecticides have been shown to give advantages in their application, while the low FB1 contamination in the final years of the study did not lead to conclusive data on the advantage of adding a fungicide. Chemicals applied did not modify A. flavus incidence or aflatoxin contamination (only detected in trace amounts).

Fumonisin B1 and zearalenone contamination of wheat in Croatia and influence of fungicide treatments

In Croatia, a trial was conducted to determine the presence of theFusariummycotoxins fumonisin B1and zearalenone in wheat kernels and to evaluate the efficacy of nine fungicides on Fusarium head blight severity as well as fumonisin B1and zearalenone accumulation in wheat grain. Fumonisin B1and zearalenone were detected in all grain samples in mean concentrations ranging from 182.0 to 446.6 µg kg-1(fumonisin B1) and from 2.59 to 5.33 µg kg-1(zearalenone). No significant differences were found among fumonisin B1and zearalenone content in wheat grain for the different fungicide treatments. No correlation was revealed between Fusarium head blight severity and fumonisin B1or zearalenone content in wheat grain, nor between fungicide efficacy and fumonisin B1or zearalenone content in wheat grain. Under conditions of high disease pressure, efficacy of the fungicides was between 85.7% (tebuconazole + triadimefon) and 72.1% (carbendazim).

Predictive modelling of temperature and water activity (solutes) on the in vitro radial growth of Botrytis cinerea Pers

The objective of this work was to develop validated models predicting the 'in vitro' effect of a(w) and temperature on the radial growth of Botrytis cinerea. The growth rate (g, mm d(-1)) of B. cinerea was calculated at three incubation temperatures (25 degrees C, 15 degrees C, 5 degrees C) and six water activities (ranging from 0.995 to 0.890). The water activity was adjusted with glucose, NaCl, glycerol, or sorbitol. Statistical analysis showed a significant effect of temperature, solute, a(w), and their two- and three-way interactions on the growth rate. No growth was observed at a(w)=0.93 in the presence of NaCl or at 0.89 in the presence of a non-ionic solute. The maximum colony growth rate decreased when the incubation temperature and water activity was lowered. Secondary models, relating the colony growth rate with a(w) or a(w) and temperature were developed. Optimum a(w) values for growth ranged from 0.981 to 0.987 in glycerol-, sorbitol-, or glucose-modified medium and were close to 1 in NaCl-modified medium. A quadratic polynomial equation was used to describe the combined effects of temperature and a(w) on g (mm d(-1)) in the presence of each solute. The highest and lowest radial growth rates were observed in models based on glucose and NaCl respectively, whatever the incubation temperature. All models prove to be good predictors of the growth rates of B. cinerea within the limits of experiments. The quadratic polynomial equation has bias factors of 0.957, 1.036, 0.950, and 0.860 and accuracy factors of 1.089, 1.070, 1.120 and 1.260 in media supplemented with glucose, NaCl, glycerol and sorbitol respectively. The results from modelling confirm the general finding that a(w) has a greater influence on fungal growth than temperature.

Contamination of pine nuts by fumonisin produced by strains of Fusarium proliferatum isolated from Pinus pinea

AIMS

To test the ability of Fusarium proliferatum strains isolated from Pinus pinea to synthesize fumonisin B(1) (FB(1)) in pine nuts.

METHOD AND RESULTS

Eleven strains were inoculated in moist sterile shelled pine nuts and whole pine nuts, and incubated for 28 days. Moist sterile maize was inoculated in parallel as an optimum substrate for FB(1) production by Fusarium species.

CONCLUSIONS

Six of the strains produced FB(1) in shelled pine nuts, and two of them did so in whole pine nuts. IMPACT AND SIGNIFICANCE OF THE STUDY: F. proliferatum is able to grow and produce FB(1) in the husk of pine nuts and the mycotoxin can be found in the nut once shelled. Consequently, FB(1) may be an important hazard in pine nuts.

Fumonisin production in rice cultures of Fusarium verticillioides under different incubation conditions using an optimized analytical method

Fumonisin B1 (FB1) and fumonisin B2 (FB2) are the main members of a family of mycotoxins produced by various fungal species belonging to the Gibberella fujikuroi complex. The present work shows the results of a comparative study of various clean-up and derivatization procedures for analysis of fumonisins in rice cultures. Fumonisins were extracted from rice with acetonitrile/water (50/50, v/v). For clean-up, three solid-phase extraction procedures were assayed (C18 cartridge, SAX cartridge, and a combination of both). Two reagents (o-phthaldialdehyde and 4-fluoro-7-nitro-benzofurazan) were studied comparatively for formation of fluorescent derivatives. The separation was carried out by LC using a fluorescence detector. The best procedure for analysis of fumonisins in rice involved clean-up with C18 cartridge and derivatization with o-phthaldialdehyde. The limit of detection was 0.010 mg kg(-1) for both toxins. In the 10-500 mg kg(-1) spiking level range, the recovery rates for FB1 and FB2 in rice varied from 94.6% to 103.6% and from 96.3% to 101.9%, respectively. The optimized analytical method for determination of fumonisins in rice was applied to the study of FB1 and FB2 production by four isolates of the G. fujikuroi species complex in rice cultures carried out at different temperatures and water activities to establish the influence of strain and environmental conditions on fumonisin production in this cereal. In general, fumonisin production was the highest at 20 degrees C and lowest at 37 degrees C. Four of the five assayed water activity (aw) values (0.97, 0.98, 0.99, and 1.0) did not affect significantly fumonisin accumulation but fumonisins were not detected in cultures when aw was 0.96.

Ecophysiology of ochratoxigenicAspergillus ochraceusandPenicillium verrucosumisolates. Predictive models for fungal spoilage prevention – a review

Ochratoxin A (OTA) is a secondary metabolite produced by several species of Aspergillus and Penicillium; among them Aspergillus ochraceus and Penicillium verrucosum are two ochratoxigenic species capable of growing in different climates and thus contamination of food crops with OTA can occur worldwide. OTA can be found in a wide range of foods such as cereals, coffee, cocoa, spices, beer, wine, dried vine fruit, grapes and meat products. OTA is toxic to animals, it presents neurotoxic, immunotoxic and nephrotoxic effects. It has been implicated in a human kidney disorder known as Balkan Endemic Nephropathy. This review focuses on the ecophysiology of ochratoxin-producing Aspergillus ochraceus and Penicillium verrucosum, the effect of environmental factors on their germination, mycelial growth, and OTA production. Knowledge of environmental conditions required for sucessive stages of fungal development represent the first step towards preventing mycotoxin formation. Predictive models for different stages of fungal development are presented, which allow prediction of the time before spoilage as a function of the abiotic factors. Finally, the implications of these studies in management of barley, coffee and grapes are described. This can help to identify the critical control points in their production, storage and distribution processes.

Do fumonisin mycotoxins occur in wheat?

The fumonisin mycotoxins are mainly produced by the fungi Fusarium verticillioides and Fusarium proliferatum, which are both field pathogens of maize. The natural occurrence of fumonisins has been verified in maize and a large range of maize-based products in many countries of the world. However, occasional reports have emerged of fumonisins being detected in wheat, despite the main producing fungi not being pathogens of this cereal. An investigation was conducted into a recent report of the natural occurrence of fumonisins in the 2003/2004 South African wheat crop at levels up to 1.7 mg/kg, as determined by immunoaffinity column cleanup and direct fluorometric measurement. An AOAC International high-performance liquid chromatographic (HPLC) method for the determination of fumonisins in maize was modified and validated for the determination of fumonisins in spiked wheat samples. HPLC analysis of the wheat samples previously found to be positive for fumonisins revealed no detectable (<5 microg/kg) fumonisins in the 30 samples analyzed. These results, which lay doubt on previous reports of fumonisins in wheat, emphasize the fact that screening methods, especially if used outside their range or matrix of applicability, can produce false positive results despite the use of immunoaffinity cleanup. Such results should be validated and confirmed with a more definitive technique.

Predictive modelling of the individual and combined effect of water activity and temperature on the radial growth of Fusarium verticilliodes and F. proliferatum on corn

The major objective of this study was to develop validated models to describe the effect of a(w) and temperature on the radial growth on corn of the two major fumonisin producing Fusaria, namely Fusarium verticilliodes and F. proliferatum. The growth of these two isolates on corn was therefore studied at water activities between 0.810-0.985 and temperatures between 15 and 30 degrees C. Minimum a(w) for growth was 0.869 and 0.854 for F. verticilliodes and F. proliferatum, respectively. No growth took place at a(w) values equal to 0.831 and 0.838 for F. verticilliodes and F. proliferatum, respectively. The colony growth rates, g (mm d(-1)) were determined by fitting a flexible growth model describing the change in colony diameter (mm) with respect to time (days). Secondary models, relating the colony growth rate with a(w) or a(w) and temperature were developed. A third order polynomial equation and the linear Arrhenius-Davey model were used to describe the combined effect of temperature and a(w) on g. The combined modelling approaches, predicting g (mm d(-1)) at any a(w) and/or temperature were validated on independently collected data. All models proved to be good predictors of the growth rates of both isolates on maize within the experimental conditions. The third order polynomial equation had bias factors of 1.042 and 1.054 and accuracy factors of 1.128 and 1.380 for F. verticilliodes and F. proliferatum, respectively. The linear Arrhenius-Davey model had bias factors of 0.978 and 1.002 and accuracy factors of 1.098 and 1.122 for F. verticilliodes and F. proliferatum, respectively. The results confirm the general finding that a(w) has a greater influence on fungal growth than temperature. The developed models can be applied for the prevention of Fusarium growth on maize and the development of models that incorporate other factors important to mould growth on maize.

Occurrence of fumonisins B1and B2in asparagus from Shandong province, P.R. China

Thirty samples of asparagus spears were collected from the fields in Shandong province, China, in July 2004, and were analysed for the occurrence of fumonisins B1 and B2 (FB1 and FB2) by HPLC coupled with electrospray ionization tandem mass spectrometry. Twenty-four samples (80%) contained fumonisins, ranging from 24 to 670 ng g(-1) (average 123 ng g(-1)) and 17 to 138 ng g(-1)(average 35 ng g(-1)) for FB1 and FB2, respectively. The total amount of fumonisins (FB1 and FB2) in all samples ranged from 47 to 714 ng g(-1) (average 158 ng g(-1)) (based on dry weight). This is the first report on the natural occurrence of FB1 and FB2 in asparagus spears in China.

Effect of water activity and temperature on growth and the relationship between fumonisin production and the radial growth of Fusarium verticillioides and Fusarium proliferatum on corn

The two major fumonisin-producing Fusarium species are Fusarium verticillioides and Fusarium proliferatum. The growth and fumonisin production of these two isolates on corn was studied at water activities (a(w)) between 0.860 and 0.975 and at temperatures between 15 and 30 degrees C. Growth rates (g, mm/day) were obtained by linear regression during the linear phase of growth. In general, growth rates for both isolates increased significantly (P < 0.05) with increases in a(w) and temperature. Both fumonisin production and radial growth (mycelial development) for both isolates increased with a(w) at all temperatures investigated, but the effect of temperature on this relationship was not obvious. The effect of temperature on fumonisin production at high a(w) values optimal for growth was only marginal, whereas at lower a(w) values the effect of temperature was more pronounced, with more fumonisin production occurring at temperatures not optimal for growth. The optimum temperature for fumonisin production was between 15 and 25 degrees C. For F. proliferatum, the optimum temperature for growth at all a(w) values, 30 degrees C, resulted in the poorest fumonisin production. For both isolates, the slowest initial rate of fumonisin production was at 15 degrees C, the temperature at which the slowest growth rates were obtained.

Fumonisin-producing strains of Fusarium: a review of their ecophysiology

This review focuses on the fumonisin-producing Fusarium species and the ecophysiology of these species. The effects of environmental biotic and abiotic factors on germination, growth, and fumonisin B1 production by Fusarium verticillioides and Fusarium proliferatum have been investigated under laboratory, field, and storage conditions. An understanding of the factors involved in production of fumonisins is the first step in preventing accumulation of these toxins.

A mathematical simulation of growth of fusarium in maize ears after artificial inoculation

ABSTRACT Fusarium spp. in maize can contaminate the grain with mycotoxins if environmental conditions are favorable for fungal growth. To quantify the relationship between growth of Fusarium spp. and environmental conditions, a mathematical model was developed to simulate growth of F. graminearum and F. verticillioides on maize ears following silk inoculation in field experiments from 1992 to 1995. Each species was inoculated separately and as a mixture of the two for 3 of the 4 years on one maize hybrid. Disease progress in ears was measured by a visual rating scale that was converted to percent visual infection. Measurements were made at regular time intervals after silks were inoculated 5 days after silk emergence. Differential equations were used to relate growth rates of Fusarium spp. in maize ears to hourly air temperature and relative humidity and to daily precipitation. Integration of these equations over time produced quantitative estimates of fungal growth. Model calculations compared well with measurements (R(2) = 0.931, standard error of estimate [SEE] = 2.11%) of percent visual disease infection of maize ears over 3 years. The model was tested against a second set of data (R(2) = 0.89, SEE = 5.9%) in which silks were inoculated at nine different times after first silk emergence for each of 2 years (1994 and 1995) with the two species of fungi on the same maize hybrid. At this time, a silk function was developed to account for changes in the susceptibility of silks to disease. F. graminearum responded to wet conditions more than F. verticillioides, and for the conditions of this experiment, grew much faster than F. verticillioides when inoculated separately. When they were inoculated together, F. graminearum growth rates were much lower, indicating some interference by F. verticillioides. During 1993, weather conditions before inoculation reduced the growth of both species in silks.