Mycoflora of Argentinian corn harvested in the main production area in 1990

Corn (Zea mays) is the main cereal produced in and exported from Argentina. The risk of contamination by mycotoxins is related to the mycoflora associated with the corn kernels. This paper reports on the identification of internal and external mycoflora of corn kernels harvested in the main production area in Argentina in 1990. A mycological survey was carried out on 178 corn samples, from five locations in that area and the isolation frequency and relative density of the prevalent fungal genera compared. GenusFusarium was the most prevalent component of the internal seedborne mycoflora in the five locations.Penicillium was prevalent in all locations, taking into account the frequency. However, this genus was predominant only in two locations, when the relative density was considered. The predominantFusarium wasF. moniliforme and the most frequently isolated species ofAlternaria, Aspergillus andPenicillium wereA. alternata, A. flavus andP. decumbens, respectively.Diplodia species were not isolated from any of the samples.     

Subchronic toxicological investigations of Fusarium moniliforme-contaminated corn,culture material,and ammoniated culture material

The fungus Fusarium moniliforme is ubiquitous on corn throughout the world and is a likely co-contaminant on corn infested with aflatoxin-producing Aspergillus flavus. Ammoniation has been used to detoxify aflatoxin-contaminated commodities. To determine the effect of ammoniation on the toxic potential of Fusarium moniliforme, male Sprague-Dawley rats were fed either diets containing 10% sound corn, ammoniated corn, corn culture material of hepatotoxic F. moniliforme strain MRC 826 (CM), or ammoniated CM for four weeks. They were observed for signs of toxicity and hematological, serum chemical and histopathological evaluations were made. Groups of male Balb/c mice were fed diets fortified with 10% sound corn or CM for four weeks and evaluated by serum chemical and histopathological means to determine the suitability of mice as a model species for investigation of F. moniliforme-induced hepatotoxicity. Ammoniation was ineffective for detoxification of the CM. Hepatotoxicity and renal toxicity of CM and ammoniated CM were qualitatively similar, although renal tubular lesions appeared more advanced in rats fed ammoniated CM. Adrenal cortical cellular vacuolation was also found in CM and ammoniated CM-fed rats, while focal seminiferous tubular degeneration and aspermia were found only in the testes of ammoniated CM-fed rats. Fumonisin B₁ concentrations of the CM and ammoniated CM diets averaged 99 and 75 ppm, respectively. CM containing 99 ppm fumonisin B₁ also produced hepatotoxicity in mice similar to that found in CM-fed rats. Thus, mice may be useful for investigations of F. moniliforme-induced hepatotoxicity.Mention of a trademark, proprietary name or vendor does not imply its approval by the US Department of Agriculture to the exclusion of others that may also be suitable.     

Enterobacter cloacae is an endophytic symbiont of corn

The bacteriumEnterobacter cloacae is presently used for biocontrol of postharvest diseases of fruits and vegetables and as a preplant seed treatment for suppression of damping-off. This bacterium has apparent affinities for several grass species, but it is not considered to be an endophyte. While screening corn for fungi and bacteria with potential for biocontrol of various corn diseases, the surface-sterilized kernels of one unknown Italian corn cultivar produced fungus-free corn seedlings with roots endophytically infected byE. cloacae. This paper describes the microscopic nature ofE. cloacae RRC 101 with corn, and the in vitro control ofFusarium moniliforme and other fungi with this bacterium. Light and electron microscopy determined that this isolate ofE. cloacae was biologically associated with corn seedling roots, where it was distributed intercellularly within the cortex and stele. This is a first report of a strain of this bacterium as an endophytic symbiont of roots. Following a topical application ofE. cloacae to kernels, and upon germination this bacterium readily infected roots of two other corn cultivars. The bacterium was observed within the endosperm of germinating corn seedling, but germination was not affected. Further, the bacterium was isolated from leaves and stems of 3- to 6-week-old seedlings indicating that the above ground portions of corn were also colonized. There was no evidence of damage to cells of the root during a three to four week observation period. This bacterium was antagonistic to several isolates of the corn pathogenFusarium moniliforme, and to two other species of fungi, all of which produce mycotoxins on corn.     

Preharvest aflatoxin contamination of maize inoculated withAspergillus flavus andFusarium moniliforme

A two-year factorial experiment was utilized to test plants field-inoculated singly and in combination withAspergillus flavus andFusarium moniliforme. Pinbar inoculations were made through the husks with conidial suspensions, and 10-ear maize samples were harvested at 60 days post-silking for aflatoxin determinations. When ears were inoculated with both fungi simultaneously,F. moniliforme reduced aflatoxin formation byA. flavus isolate NRRL 3357 by approximately two-thirds.F. moniliforme had no significant effect on naturally occurring aflatoxin contamination byA. flavus. This may be due to the timing of infection by both fungi in the field. In nature,A. flavus andF. moniliforme respond differently to the environment, offering one explanation of whyF. moniliforme did not measurably affect the other fungus.     

Production of fumonisins byFusarium species of Taiwan

Twenty-nineFusarium species isolated from various sources in different districts of Taiwan were tested for their ability to produce fumonisins in corn cultures. OnlyFusarium moniliforme produced fumonisin B₁ (FB₁) and fumonisin B₂ (FB₂). The finding that the other 28Fusarium species produced neither FB₁ nor FB₂ is preliminary because only one strain per species was studied. The detection of FB₁ and FB₂ in cultures ofF. moniliforme was demonstrated by TLC and HPLC, and FB₁ was further confirmed by mass spectrometry. In a separate experiment, in which 38 strains ofF. moniliforme were tested for fumonisins, approximately 66% (25/38) produced FB₁ and/or FB₂. Of the 25 strains, 14 produced only FB₁ and 11 produced both FB₁ and FB₂, and the amounts of FB₁ and FB₂ produced by different strains varied greatly. This is the first report that fumonisins are found in corn cultures experimentally infected withF. moniliforme strains from Taiwan. It is safe to assume that fumonisin producing strains ofF. moniliforme are widely distributed among the economic crops such as corn, rice, sugarcane, and sorghum throughout the Island.Abbreviations FB₁ Fumonisin B₁ - FB₂ Fumonisin B₂ - OPA o-phthalidialdehyde     

Identification of deoxynivalenol, 3-acetyldeoxynivalenol and zearalenone in the galactose oxidase-producing fungus Dactylium dendroides

The galactose oxidase-producing fungus Dactylium dendroides was re-identified as a Fusarium species. Fungi of this genus are well known for the production of mycotoxins. Verification of growth of this fungus on rice, corn and liquid medium described for the production of galactose oxidase is provided to determine whether the fungus could produce Fusarium toxins, namely, moniliformin, fusaric acid, fumonisin, zearalenone and the trichothecenes, deoxynivalenol, 3-acetyldeoxynivalenol, fusarenone, nivalenol, diacetoxyscirpenol, neosolaniol, and toxin T-2. Under the culture conditions used, deoxynivalenol, 3-acetyldeoxynivalenol and zearalenone were detected in the fungal culture medium. The finding is consistent with the hypothesis that the fungus is in fact a Fusarium species. This revised version was published online in July 2006 with corrections to the Cover Date.     

The implications of naturally occurring levels of fumonisins in corn for human and animal health

Contamination of corn with the fungus Fusarium moniliforme and its secondary metabolites, the fumonisins, has been associated with several human and animal diseases. This paper summarizes present knowledge and presents new data on the levels of fumonisins present in foods and feeds associated with these diseases as well as in commercial corn and corn-based products. The doses of fumonisins to which humans and animals consuming these products would be exposed are compared with those doses known to produce LEM in horses and hepatocarcinogenesis in rats. It is concluded that the known naturally occurring levels of fumonisins present a potential threat to human and animal health and realistic tolerance levels need to be set.     

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.     

Effect of soil solarization on corn stalk rot

Seven weeks solarization of irrigated soil raised its temperature by 11.5°C over non-solarized soil at 10 cm depth and effectively controlled weeds (98.5%), stalk borer (8.9%) and stalk rot disease (69.1%) in corn. Solarization also reduced symptoms of Fusarium moniliforme and Macrophomina phaseolina significantly by 64.2% and 78.4%, respectively, and completely controlled M. phaseolina in corn cultivars, viz. Pool-10, Shaheen and Gauher. Whereas symptoms of F. moniliforme were observed in these cultivars, Fusarium graminearum was not observed except in two cultivars, Shaheen and Akbar. Growth of crop planted in solarized plots was better and it yielded almost one to three times more grains in cultivars under test. Soil analysis immediately following solarization revealed that essential elements were readily available in simpler forms, which may have increased pest resistance and reduced stalk breakage.     

A new fumonisin from solid cultures of Fusarium moniliforme

A new fumonisin has been isolated from Fusarium moniliforme isolate MRC826 grown on corn. It was shown by NMR and mass spectrometry to be an isomer of fumonisin B₂ that has free hydroxyl groups at C-3 and C-10 instead of the normal C-3 and C-5. This new fumonisin was detected in cultures of most isolates of F. moniliforme that were examined and was usually present at concentrations similar to those of fumonisin B₂. Two isolates of F. moniliforme that produce significantly higher levels of this new isomer were identified.Abbreviations ELEM equine leukoencephalomalacia Mention of companies or products by name does not imply their endorsement by the US Department of Agriculture over others not cited.     

Production of moniliformin by Canadian isolates of Fusarium

Twenty-eight Canadian isolates of Fusarium were tested for their ability to produce moniliformin in corn. Both F. moniliforme (2/6 isolates) and F. subglutinans (11/15 isolates) produced the mycotoxin, while F. graminearum did not. Field-corn inoculated with F. moniliforme M3783 was able to support production of both moniliformin and fusarin C.     

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.     

Fumonisins: Isolation,chemical characterization and biological effects

The fumonisin B mycotoxins (FB₁ and FB₂) have been purified and characterized from corn cultures of Fusarium moniliforme strain MRC 826. Fumonisin B₁ (FB₁, the major fumonisin produced in culture, has been shown to be responsible for the major toxicological effects of the fungus in rats, horses and pigs. Recent investigations on the purification of compounds with chromatographic characteristics similar to FB₁ have led to the identification of two new fumonisins, FB₃ and FB₄. Fumonisins A₁ and A₂, the N-acetyl derivatives of FB₁ and FB₂ respectively, were also purified and shown to be secondary metabolites of the fungus. Short-term carcinogenesis studies in a rat liver bioassay indicated that over a period of 15 to 20 days, at dietary levels of 0.05–0.1%, FB₂ and FB₃ closely mimic the toxicological and cancer initiating activity of FB₁ and thus could contribute to the toxicological effects of the fungus in animals. In contrast, no biological activity could be detected for FA₁ under identical experimental conditions. These studies and others have indicated that the fumonisin B mycotoxins, although lacking mutagenicity in the Salmonella test or genotoxicity in the DNA repair assays in primary hepatocytes, appear to induce resistant hepatocytes similar to many known hepatocarcinogens.     

Biological efficacy of <Emphasis Type="Italic">Trichoderma harzianum</Emphasis> isolate to control some fungal pathogens of wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis>) in Turkey

Gaeumannomyces graminis var. tritici, Fusarium culmorum and F. moniliforme are highly important and widespread pathogens of wheat in Turkey. Trichoderma isolates have been used as biocontrol agents to protect plants against soilborne diseases in several crops. The present work was carried out to evaluate the potential of Trichoderma harzianum isolate T1 as biocontrol agents for G. graminis, F. culmorum and F. moniliforme under field conditions in 2001 and 2002. Quantitative differences were found in microbial number in soil. T. harzianum T1 had considerable effect on population densities of the tested pathogens. The total number of G. graminis, F. culmorum and F. moniliforme were lower in the T. harzianum T1 application made to seed. T. harzianum T1 application to seed had increasing affect on the yield components of wheat through better control over pathogens. The greatest counts of T. harzianum T1 were detected on root segments. Seed application by T. harzianum T1 had increasing effect on yield components of wheat.     

Lagenidium infection in eggs and larvae of mangrove crab (Scylla serrata) produced in Indonesia

A fungal infection occurred in the eggs and larvae of mangrove crab (Scylla serrata) in seed production in Bali, Indonesia. The causative fungus was classified as a member of the genusLagenidium (Oomycetes, Lagenidiales). After comparison of its biological and physiological characteristics with those ofL. callinectes ATCC 24973, a known parasite of various crustaceans, was concluded that the isolate is a new species ofLagenidium, L. thermophilum, because of its rapid and thermotolerant growth and unique discharge process. Fungal growth was observed on PYG agar containing 0–5.0% (w/v) NaCl and 0–2.5% (w/v) KCI. Similar pathogenicity toward the zoeae of swimming crab (Portunus trituberculatus) was demonstrated.     

Expression of the gene encoding the PR-like protein PRms in germinating maize embryos

Summary The PRms protein is a pathogenesis-related (PR)-like protein whose mRNA accumulates during germination of maize seeds. Expression of the PRms gene is induced after infection of maize seeds with the fungus Fusarium moniliforme. To further our investigations on the expression of the PRms gene we examined the accumulation of PRms mRNA in different tissues of maize seedlings infected with E. moniliforme and studied the effect of fungal elicitors, the mycotoxin moniliformin, the hormone gibberellic acid, and specific chemical agents. Our results indicate that fungal infection, and treatment either with fungal elicitors or with moniliformin, a mycotoxin produced by F. monilforme, increase the steady-state level of PRms mRNA. PRms mRNA accumulation is also stimulated by the application of the hormone gibberellic acid or by treatment with silver nitrate, whereas acetylsalicylic acid has no effect. In situ RNA hybridization in isolated germinating embryo sections demonstrates that the PRms gene is expressed in the scutellum, particularly in a group of inner cells, and in the epithelium lying at the interface of the scutellum and the endosperm. The pattern of expression of the PRms gene closely resembles that found for hydrolytic enzymes, being confined to the scutellum and the aleurone layer of the germinating maize seed. Our results suggest that the PRms protein has a function during the normal process of seed germination that has become adapted to serve among the defence mechanisms induced in response to pathogens during maize seed germination.     

Protection of maize seedlings byFusarium moniliforme against infection byFusarium graminearum in the soil

The incidence ofFusarium moniliforme in surface-sterilized kernels in two commercial South African white maize cultivars was 64% and 6%, respectively. Heat treatment completely eliminated seedborneF. moniliforme from kernels of both cultivars. Heat treated, uncontaminated maize germlings were pre-inoculated with different isolates ofF. moniliforme and planted in steam-treated soil containing inoculum of different isolates ofF. graminearum Group 1 and Group 2. Seedling weights of germlings pre-inoculated with some isolates ofF. moniliforme were significantly higher than those of controls when exposed to some isolates ofF. graminearum in the soil. The protective effect of pre-inoculation withF. moniliforme was particularly evident in maize seedlings exposed to inoculum of an aggressive isolate ofF. graminearum Group 1. This is the first report of the protection of maize seedlings byF. moniliforme against infection byF. graminearum in the soil.     

Seed predation,pathogen infection and life-history traits in Brassica rapa

Herbivory and disease can shape the evolution of plant populations, but their joint effects are rarely investigated. Families of plants of Brassica rapa (Brassicaceae) were grown from seeds collected in two naturalized populations in an experimental garden. We examined leaf infection by the fungus Alternaria, seed predation by a gall midge (Cecidomyiidae) and plant life-history traits. Plants from one population had heavier seeds, were more likely to flower, had less fungal infection, had more seed predation and were more fecund. Fungal infection score and seed predation rate increased with plant size, but large plants still had the greatest number of undamaged fruits. Spatial heterogeneity in the experimental garden was significant; seed predation rate and fecundity varied among blocks. An apparent tradeoff existed between susceptibility to disease and seed predation: plants with the highest fungal infection score had the lowest seed predation rate. Alternaria infection varied between populations, but the disease had no effect on fecundity. Seed predation did reduce fecundity. Damaged fruits had 31.4% fewer intact seeds. However, evidence for additive genetic variation in resistance to seed predation was weak. Therefore, neither disease nor seed predation was likely to be a strong agent of genetically based fecundity selection.     

Occurrence and distribution of <Emphasis Type="Italic">Microdochium nivale</Emphasis> and <Emphasis Type="Italic">Fusarium</Emphasis> species isolated from barley,durum and soft wheat grains in France from 2000 to 2002

Fusarium Head Blight of small grain cereal is a disease of growing concern in Europe. Along with Microdochium nivale, several species of Fusarium may be associated with the disease, including species that are potentially toxigenic. This paper describes the results of a large scale survey of the variety and frequency of different Fusarium species and M. nivale in France. A total of 749 soft wheat, durum wheat and barley samples were collected and analyzed from 2000 to 2002. The most frequent species isolated were F.graminearum, F. avenaceum and F. poae. The frequency of F. poae seems to have increased while M.nivale and F. culmorum appear less frequent than previously described in France. Other Fusarium species detected in decreasing prevalence were F. tricinctum, F. equiseti, F. acuminatum, F. sambucinum, F.sporotrichioides, F. moniliforme, F. heterosporum, F. subglutinans and F. oxysporum. All the most frequent pathogenic species and also the less pathogenic ones were frequently associated with individual fields. The implications of these associations for the protection of cereals crops and for contamination by mycotoxins are discussed.