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.     

Purified moniliformin does not affect the force or rate of contraction of isolated guinea pig atria

Aspergillus flavus Link ex Fries and A. parasiticus Speare can invade peanut kernels and under certain environmental conditions produce unacceptable levels of the mycotoxin aflatoxin. A concerted effort is underway to reduce aflatoxin contamination in peanut and peanut products. A potentially effective method of control in peanut is the discovery and use of genes for resistance to either fungal invasion or aflatoxin formation. The objective of the present experimental study was to develop an effective and efficient procedure for screening individual plants or pods of single plants for resistance to invasion by the aflatoxigenic fungi and subsequent aflatoxin production. Methods of obtaining adequate drought-stress and fungal infection were developed through this series of experiments. By completely isolating the pods from the root zone and imposing drought-stress only on pegs and pods, high levels of fungal infection were observed. High amounts of preharvest aflatoxin accumulation were also produced by completely isolating the pods from the root zone. Mid-bloom inoculation with A. parasiticus-contaminated cracked corn and drought-stress periods of 40 to 60 days were the most effective procedures. This technique was used to assess peanut genotypes previously identified as being partially resistant to A. parasiticus infection or aflatoxin contamination, and segregating populations from four crosses. Variability in aflatoxin contamination was found among the 11 genotypes evaluated, however, none were significantly lower than the standard cultivars. Broad-sense heritability of four crosses was estimated through evaluation of seed from individual plants in the F₂ generation. The heritability estimates of crosses GFA-2 × NC-V11 and Tifton-8 × NC-V11 were 0.46 and 0.29, respectively, but mean aflatoxin contamination levels were high (73,295 and 27,305 ppb). This greenhouse screening method could be an effective tool when genes for superior aflatoxin resistance are identified.Cooperative investigation of the USDA-ARS and the University of Georgia, College of Agriculture.     

Evaluation of biological control formulations to reduce aflatoxin contamination in peanuts

A two-year study was conducted to evaluate the efficacy of three formulations of nontoxigenic strains of Aspergillus flavus and Aspergillus parasiticus to reduce preharvest aflatoxin contamination of peanuts. Formulations included: (1) solid-state fermented rice; (2) fungal conidia encapsulated in an extrusion product termed Pesta; (3) conidia encapsulated in pregelatinized corn flour granules. Formulations were applied to peanut plots in 1996 and reapplied to the same plots in 1997 in a randomized design with four replications, including untreated controls. Analysis of soils for A. flavus and A. parasiticus showed that a large soil population of the nontoxigenic strains resulted from all formulations. In the first year, the percentage of kernels infected by wild-type A. flavus and A. parasiticus was significantly reduced in plots treated with rice and corn flour granules, but it was reduced only in the rice-treated plots in year two. There were no significant differences in total infection of kernels by all strains of A. flavus and A. parasiticus in either year. Aflatoxin concentrations in peanuts were significantly reduced in year two by all formulation treatments with an average reduction of 92%. Reductions were also noted for all formulation treatments in year one (average 86%), but they were not statistically significant because of wide variation in the aflatoxin concentrations in the untreated controls. Each of the formulations tested, therefore, was effective in delivering competitive levels of nontoxigenic strains of A. flavus and A. parasiticus to soil and in reducing subsequent aflatoxin contamination of peanuts.     

Association of aflatoxin biosynthesis and sclerotialdevelopment in Aspergillus parasiticus

Secondary metabolism in fungi is frequently associated with asexual and sexual development. Aspergillus parasiticus produces aflatoxins known to contaminate a variety of agricultural commodities. This strictly mitotic fungus, besides producing conidia asexually, produces sclerotia, structures resistant to harsh conditions and for propagation. Sclerotia are considered to be derived from the sexual structure, cleistothecia, and may represent a vestige of ascospore production. Introduction of the aflatoxin pathway-specific regulatory gene, aflR, and aflJ, which encoded a putative co-activator, into an O-methylsterigmatocystin (OMST)-accumulating strain,A. parasiticus SRRC 2043, resulted in elevated levels of accumulation of major aflatoxin precursors, including norsolorinic acid (NOR), averantin (AVN), versicolorin A (VERA) and OMST. The total amount of these aflatoxin precursors, NOR, VERA, AVN and OMST, produced by the aflR plus aflJ transformants was two to three-fold that produced by the aflR transformants. This increase indicated a synergisticeffect of aflR and aflJ on the synthesis of aflatoxin precursors. Increased production of the aflatoxin precursors was associated with progressive decrease in sclerotial size, alteration in sclerotial shape and weakening in the sclerotial structure of the transformants. The results showed that sclerotial development and aflatoxin biosynthesis are closely related. We proposed that competition for a common substrate, such as acetate, by the aflatoxin biosynthetic pathway could adversely affect sclerotial development in A. parasiticus. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of peanut tannin extracts on growth of Aspergillus parasiticus and aflatoxin production

Twenty-three peanut (Arachis hypogaea L.) genotypes were evaluated for kernel resistance to Aspergillus parasiticus Spear. colonization and aflatoxin contamination when incubated under high relative humidity. Also, tannin-containing extracts from kernel coats (testae) and cotyledons of these genotypes were prepared and tested for their effect on A. parasiticus growth and aflatoxin production in vitro. The lowest degree of colonization, less than 30% was noted in kernels from the genotypes, Toalson x UF 73-4022 (selections TX-798731 and TX-798736), A72118, SN 55-437, PI337409, and Florunner. Genotypes with low levels of colonization also had the lowest aflatoxin contamination. The coefficient of correlation between infection frequency and aflatoxin contamination was 0.66. Higher levels of tannins were detected in the testae (23.9–97.2 mg g tissue) compared to the cotyledons (0.17–0.82 mg g tissue). Some of the methanol-extracted and water-soluble tannin extracts from testae and cotyledons, when incorporated in yeast extract sucrose liquid medium (100 mg l), significantly inhibited A. parasiticus growth and reduced the levels of aflatoxin produced. There was no overall correlation between the peanut genotypes and the influence of tannin extracts on A. parasiticus growth and aflatoxin production. However, correlations were higher for specific genotypes. For example, the coefficient of correlation between the ability of tannin extracts from testae of genotypes PI337409 and TX-798736 to inhibit aflatoxin production was 0.93 and 0.85 respectively.     

Occurrence of Aspergillus section Flavi and aflatoxin B1 in corn genotypes and corn meal in Argentina

A study has been carried out in Argentina on samples of corn genotypes from a breeding station as well as in commercially available corn meal. All samples were analyzed for fungal infection and aflatoxin B₁.Mycological analysis of corn genotypes showed the presence of three principal genera of filamentous fungi Fusarium (100%), Penicillium (67%) and Aspergillus (60%). In the genus Fusarium three species were identified, F. moniliforme (42%), F. nygamai (56%) andF. proliferatum (1.8%). Eight species ofPenicillium were identified, the predominant species isolated were P. minioluteum, P. funiculosum and P. variabile. In the genus ranked third in isolation frequency, two species were identified, A. flavus and A. parasiticus, the percentage of infection was 78% and 21%, respectively. Only one corn genotype was contaminated with aflatoxin B₁ at a level of 5 ppb. The cornmeal samples showed great differences in fungal contamination, the values ranging from 1 × 10¹ to 7 × 10⁵ cfu g^–1. Fusarium (68%), Aspergillus (35%) and Penicillium (21%) were the most frequent genera isolated. Among the genus, Aspergillus, A. parasiticus (38%) was the most frequent species isolated. All the samples of corn meal were negative to aflatoxin B₁. These results indicate a low degree of human exposure to aflatoxins in Argentina through the ingestion of maize or corn meal.This revised version was published online in October 2005 with corrections to the Cover Date.     

Elucidation of <Emphasis Type="Italic">veA</Emphasis>-dependent genes associated with aflatoxin and sclerotial production in <Emphasis Type="Italic">Aspergillus flavus</Emphasis> by functional genomics

The aflatoxin-producing fungi, Aspergillus flavus and A. parasiticus, form structures called sclerotia that allow for survival under adverse conditions. Deletion of the veA gene in A. flavus and A. parasiticus blocks production of aflatoxin as well as sclerotial formation. We used microarray technology to identify genes differentially expressed in wild-type veA and veA mutant strains that could be involved in aflatoxin production and sclerotial development in A. flavus. The DNA microarray analysis revealed 684 genes whose expression changed significantly over time; 136 of these were differentially expressed between the two strains including 27 genes that demonstrated a significant difference in expression both between strains and over time. A group of 115 genes showed greater expression in the wild-type than in the veA mutant strain. We identified a subgroup of veA-dependent genes that exhibited time-dependent expression profiles similar to those of known aflatoxin biosynthetic genes or that were candidates for involvement in sclerotial production in the wild type.     

Aflatoxin contamination caused by natural fungal infection of preharvest corn

Summary Aflatoxin contamination of developing corn (Zea mays L.) kernels caused by natural infection byAspergillus flavus Link ex Fries was studied in hybrids developed for the U.S. corn belt and for the southern U.S. and grown at diverse locations in 1977. Planting dates were staggered to examine the effect of crop maturity on infection by the toxin-producing fungus. A broad range of toxin values was observed at harvest; some levels exceeded the highest that had been previously recorded in corn. The highest concentration of aflatoxin B₁ detected was 8030 ppb. Levels of toxin differed significantly among planting dates in Florida and Georgia; the second planting date at these locations contained the highest toxin levels. Elevated concentrations of toxin were characteristic of kernel samples from southern locations and southeast Missouri; at these locations samples from hybrids developed for the south had significantly lower levels of toxin than hybrids developed for the corn belt. Ears with heavy insect damage had higher toxin levels than ears with less evidence of insect attack.Mention of firm names or trade products does not imply that they are endorsed or recommended by the U.S. Department of Agriculture over other firms or similar products not mentioned.     

Interactions of Fusarium moniliforme,its metabolites and bacteria with corn

Fusarium moniliforme Sheldon is an economically important pathogen of corn (Zea mays L.) which causes stalk, root and ear rot. Several mycotoxins have also been isolated, identified and implicated in both animal and human toxicoses. The fungus can be disseminated in symptomless corn seed and can also survive in crop residues in the soil. Asymptomatic infection may be related to different corn cultivars, fungal strains, and environmental factors. Symptomatic expression of pathogenicity may vary, but usually the result of such infections is death of the plant. The greatest concern is the asymptomatic infection, since it is in this form that fungal toxins may surreptitiously enter animal and human food chains. F. moniliforme produces both fusaric acid, which is phytotoxic to corn and interferes with seed germination, and plant growth regulators that may affect pathogenicity of the fungus or be associated with the production of mycotoxins. Other metabolites, including fusarin C, moniliformin, and the fumonisins, may or may not be phytotoxic, but are associated with animal and human toxicoses. The control of F. moniliforme in corn is therefore quite important. One potential means to accomplish this reduction is biocontrol by the application of antagonistic rhizobacteria to corn kernels at planting. To be effective the bacteria must be able to colonize the corn root system and be able to prevent root infection by successful competing with F. moniliforme which may be accomplished by siderophore and or antibiotic activity.     

Separate and combined applications of nontoxigenic Aspergillus flavus and A. parasiticus for biocontrol of aflatoxin in peanuts

A 2-year study was carried out to determine the effect of applying nontoxigenic strains of Aspergillus flavus and A. parasiticus to soil separately and in combination on preharvest aflatoxin contamination of peanuts. A naturally occurring, nontoxigenic strain of A. flavus and a UV-induced mutant of A. parasiticus were applied to peanut soils during the middle of each of two growing seasons using a formulation of conidia-coated hulled barley. In addition to an untreated control, treatments included soil inoculated with nontoxigenic A. flavus only, soil inoculated with nontoxigenic A. parasiticus only, and soil inoculated with a mixture of the two nontoxigenic strains. Plants were exposed to late-season drought conditions that were optimal for aflatoxin contamination. Results from year one showed that significant displacement (70%) of toxigenic A. flavus occurred only in peanuts from plots treated with nontoxigenic A. flavus alone; however, displacement did not result in a statistically significant reduction in the mean aflatoxin concentration in peanuts. In year two, soils were re-inoculated as in year one and all treatments resulted in significant reductions in aflatoxin, averaging 91.6%. Regression analyses showed strong correlations between the presence of nontoxigenic strains in peanuts and aflatoxin reduction. It is concluded that treatment with the nontoxigenic A. flavus strain alone is more effective than the A. parasiticus strain alone and equally as effective as the mixture. The U.S. Government’s right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged.     

Conidial movement of nontoxigenic Aspergillus flavus and A. parasiticus in peanut fields following application to soil

The use of nontoxigenic strains of Aspergillus flavus and A. parasiticus in biological control effectively reduces aflatoxin in peanuts when conidium-producing inoculum is applied to the soil surface. In this study, the movement of conidia in soil was examined following natural rainfall and controlled precipitation from a sprinkler irrigation system. Conidia of nontoxigenic A. flavus and A. parasiticus remained near the soil surface despite repeated rainfall and varying amounts of applied water from irrigation. In addition, rainfall washed the conidia along the peanut furrows for up to 100 meters downstream from the experimental plot boundary. The dispersal gradient was otherwise very steep upstream along the furrows and in directions perpendicular to the peanut rows. The retention of biocontrol conidia in the upper soil layers is likely important in reducing aflatoxin contamination of peanuts and aerial crops such as corn and cottonseed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Efficacy of inoculative releases of Trichogramma ostriniae (Hymenoptera: Trichogrammatidae) against European corn borer Ostrinia nubilalis (Lepidoptera: Crambidae) in field corn

We evaluated the egg parasitoid Trichogramma ostriniae (Hymenoptera: Trichogrammatidae) to control European corn borer [Lepidoptera: Crambidae: Ostrinia nubilalis (Hübner)] in field corn in 2001 and 2002. Inoculative releases of 75,000 T. ostriniae/ha occurred in New York and Virginia in 5–10 cornfields per state when corn was at mid-whorl. Incidence of egg mass parasitism, number of stalk tunnels, incidence of ear damage, and whole-plant yield were evaluated. Parasitism of European corn borer egg masses ranged from 0 to 75% in release plots and was greater in release plots than in control plots. Individual comparisons between paired release and control plots showed no reductions in either stalk or ear damage. However, when data were combined across both years and fields, stalk and ear damage were significantly reduced in New York. In Virginia, no significant differences were detected using data obtained from one year. There were no differences in yield between release and control plots. Low densities of European corn borer, drought conditions in 1 year, and a larger plant canopy in field corn are possible reasons why T. ostriniae releases provided less control than has been observed in previous trials in sweet corn. Additional research focused on improved timing and frequency and number of releases is warranted.     

Survey of Vietnamese Peanuts,Corn and Soil for the Presence of <Emphasis Type="Italic">Aspergillus flavus</Emphasis> and <Emphasis Type="Italic">Aspergillus parasiticus</Emphasis>

Aspergillus flavus and Aspergillus parasiticus cause perennial infection of agriculturally important crops in tropical and subtropical areas. Invasion of crops by these fungi may result in contamination of food and feed by potent carcinogenic aflatoxins. Consumption of aflatoxin contaminated foods is a recognised risk factor for human hepatocellular carcinoma (HCC) and may contribute to the high incidence of HCC in Southeast Asia. This study conducted a survey of Vietnamese crops (peanuts and corn) and soil for the presence of aflatoxigenic fungi and used microsatellite markers to investigate the genetic diversity of Vietnamese Aspergillus strains. From a total of 85 samples comprising peanut (25), corn (45) and soil (15), 106 strains were isolated. Identification of strains by colony morphology and aflatoxin production found all Vietnamese strains to be A. flavus with no A. parasiticus isolated. A. flavus was present in 36.0% of peanut samples, 31.1% of corn samples, 27.3% of farmed soil samples and was not found in virgin soil samples. Twenty-five per cent of the strains produced aflatoxins. Microsatellite analysis revealed a high level of genetic diversity in the Vietnamese A. flavus population. Clustering, based on microsatellite genotype, was unrelated to aflatoxin production, geographic origin or substrate origin.     

Physiological variation among native and exotic winter annual plants associated with microbiotic crusts in the Mojave Desert

An experiment was established in 1992 in eastern Ontario, Canada to determine the effects of crop rotation (continuous maize, soybean-maize and alfalfa-maize) and nitrogen (N) amendment [0, 100 and 200 kg N ha^–1 of fertilizer (NH₄NO₃), and 50 and 100 Mg ha^–1 (wet wt.) each of stockpiled and rotted dairy manure] on maize production and soil properties. From 1997 to 1999, an additional study was added to the experiment to investigate treatment effects on the susceptibility of maize hybrids to gibberella ear rot. A moderately resistant and a susceptible hybrid were planted in each plot and inoculated with a macroconidial suspension of Fusarium graminearum by both the silk channel injection and the kernel-wound techniques. At harvest, ears were rated for the severity of disease symptoms and harvested kernels were analyzed for the mycotoxin deoxynivalenol (DON). The greatest number of significant N effects were found in the continuous maize treatments and with the susceptible hybrid. Most N amendments decreased both disease severity and DON accumulation in the susceptible hybrid. The most consistent effect was a decrease in disease severity with 100 kg N ha^–1 fertilizer and an increase in disease severity with the higher rate of 200 kg N ha^–1. This study is the first to report on the effects of soil N amendments on gibberella ear rot susceptibility.     

Proteomic analysis of the maize rachis: potential roles of constitutive and induced proteins in resistance to Aspergillus flavus infection and aflatoxin accumulation

Infection of the maize (Zea mays L.) with aflatoxigenic fungus Aspergillus flavus and consequent contamination with carcinogenic aflatoxin is a persistent and serious agricultural problem causing disease and significant crop losses worldwide. The rachis (cob) is an important structure of maize ear that delivers essential nutrients to the developing kernels and A. flavus spreads through the rachis to infect kernels within the ear. Therefore, rachis plays an important role in fungal proliferation and subsequent kernel contamination. We used proteomic approaches and investigated the rachis tissue from aflatoxin accumulation resistant (Mp313E and Mp420) and susceptible (B73 and SC212m) maize inbred lines. First, we compared rachis proteins from resistant and susceptible inbred lines, which revealed that the young resistant rachis contains higher levels of abiotic stress-related proteins and proteins from phenylpropanoid metabolism, whereas susceptible young rachis contains pathogenesis-related proteins, which are generally inducible upon biotic stress. Second, we identified A. flavus-responsive proteins in rachis of both resistant and susceptible genotypes after 10- and 35-day infection. Differential expression of many stress/defense proteins during rachis juvenility, maturation and after A. flavus challenge demonstrates that resistant rachis relies on constitutive defenses, while susceptible rachis is more dependent on inducible defenses.     

Influence of trace elements and nitrogen sources on versicolorin production by a mutant strain of Aspergillus parasiticus

A mutant strain of Aspergillus parasiticus blocked in aflatoxin biosynthesis accumulates versicolorin A and versicolorin C. The effect of trace elements on the growth and versicolorin production by this strain was studied in a defined medium. The omission of manganese was slightly stimulatory to versicolorin production; when zinc was omitted from the medium, no detectable versicolorins were produced. Experiments on nitrogen sources in a highsucrose medium indicated that fourfold to fivefold increases in versicolorin yields could be obtained by substituting 3 ml/l corn steep liquor or 0.1 M NH₄NO₃ for the 0.023 M (NH₄)₂SO₃ used previously as the nitrogen source in studies on versicolorin production by this strain. These improved yields will facilitate attempts to accumulate enough versicolorin A and versicolorin C for toxicity and carcinogenicity testing. Chromatographic profiles of mycelial extracts of cultures grown in a defined medium with 0.1 M NH₄NO₃ as the nitrogen source revealed 2 previously unrecognized compounds. The accumulation of these new metabolites in a mutant blocked in aflatoxin production may indicate that they are biosynthetically related to aflatoxin.     

Involvement of the nadA gene in formation of G-group aflatoxins in Aspergillus parasiticus

The nadA gene is present at the end of the aflatoxin gene cluster in the genome of Aspergillus parasiticus as well as in Aspergillus flavus. RT-PCR analyses showed that the nadA gene was expressed in an aflatoxin-inducible YES medium, but not in an aflatoxin-non-inducible YEP medium. The nadA gene was not expressed in the aflR gene-deletion mutant, irrespective of the culture medium used. To clarify the nadA gene’s function, we disrupted the gene in aflatoxigenic A. parasiticus. The four nadA-deletion mutants that were isolated commonly accumulated a novel yellow-fluorescent pigment (named NADA) in mycelia as well as in culture medium. When the mutants and the wild-type strain were cultured for 3 days in YES medium, the mutants each produced about 50% of the amounts of G-group aflatoxins that the wild-type strain produced. In contrast, the amounts of B-group aflatoxins did not significantly differ between the mutants and the wild-type strain. The NADA pigment was so unstable that it could non-enzymatically change to aflatoxin G₁ (AFG₁). LC–MS measurement showed that the molecular mass of NADA was 360, which is 32 higher than that of AFG₁. We previously reported that at least one cytosol enzyme, together with two other microsome enzymes, is necessary for the formation of AFG₁ from O-methylsterigmatocystin (OMST) in the cell-free system of A. parasiticus. The present study confirmed that the cytosol fraction of the wild-type A. parasiticus strain significantly enhanced the AFG₁ formation from OMST, whereas the cytosol fraction of the nadA-deletion mutant did not show the same activity. Furthermore, the cytosol fraction of the wild-type strain showed the enzyme activity catalyzing the reaction from NADA to AFG₁, which required NADPH or NADH, indicating that NADA is a precursor of AFG₁; in contrast, the cytosol fraction of the nadA-deletion mutant did not show the same enzyme activity. These results demonstrated that the NadA protein is the cytosol enzyme required for G-aflatoxin biosynthesis from OMST, and that it catalyzes the reaction from NADA to AFG₁, the last step in G-aflatoxin biosynthesis.     

The appearance of an enzyme activity catalysing the conversion of norsolorinic acid to averantin in Aspergillus parasiticus cultures

The activity of the enzyme responsible for the conversion of norsolorinic acid to averantin was studied in two strains of Aspergillus parasiticus. Cell-free extracts of the enzyme were purified from different aged mycelia and little activity was found prior to 24 hours after inoculation but this quickly reached a maximum at 48 hours and declined thereafter. Both strains of A. parasiticus, one in aflatoxin producing strain, the other a versicolorin A accumulating mutant, showed this trend. It was concluded that the enzyme responsible for this conversion was a secondary metabolic enzyme and was distinct from alcohol and mannitol dehydrogenases.     

Fungi associated with food and feed commodities from Ecuador

Freshly harvested soybean, rice and corn from farms and corn-based pelleted feeds were collected from ranches from the coastal and mountain regions in Ecuador during 1998, and assessed for fungal contamination. The most prevalent fungi on pelleted feed were Aspergillus flavus and Fusarium graminearum. The prevalent fungi recovered from soybean were F. verticillioides, F. semitectum, Aspergillus flavus and A. ochraceus. In rice, F. oxysporum was the most prevalent toxigenic fungal species recorded, followed by F. verticillioides and A. flavus. In corn, F. verticillioides was the most prevalent fungus isolated in both the coastal and mountain regions, with high isolation frequencies of A. flavus and A. parasiticus at the coast. Based on the toxigenic species recovered, ochratoxin A may pose a contamination risk for soybean. A higher probability of aflatoxin contamination of corn was found in the coastal samples compared to those of the mountain region, while a risk of fumonisin contamination of corn exists in both regions.This revised version was published online in October 2005 with corrections to the Cover Date.