Preharvest Maize Research Articles

Seed Priming with Rhizospheric Bacillus subtilis: A Smart Strategy for Reducing Fumonisin Contamination in Pre-Harvest Maize.

Maize, one of the most important cereal crops in Bangladesh, is severely contaminated by fumonisin, a carcinogenic secondary metabolite produced by Fusarium including Fusarium proliferatum. Biocontrol with Bacillus strains is an effective approach to controlling this F. proliferatum as Bacillus has proven antagonistic properties against this fungus. Therefore, the present study aimed to determine how native Bacillus strains can reduce fumonisin in maize cultivated in Bangladesh, where BDISO76MR (Bacillus subtilis) strains showed the highest efficacy both in vitro in detached cob and in planta under field conditions. The BDISO76MR strain could reduce the fumonisin concentration in detached cob at 98.52% over untreated control, by inhibiting the conidia germination and spore formation of F. proliferatum at 61.56% and 77.01%, respectively in vitro. On the other hand, seed treatment with formulated BDISO76MR showed higher efficacy with a reduction of 97.27% fumonisin contamination compared to the in planta cob inoculation (95.45%) over untreated control. This implies that Bacillus-based formulation might be a potential approach in mitigating fumonisin contamination in maize to ensure safe food and feed.

Maize Aspergillus section Flavi isolate diversity may be distinct from that of soil and subsequently the source of aflatoxin contamination

Aspergillus section Flavi (Flavi) is a diverse group of fungal species whose common members include A. flavus and A. parasiticus. These are well-known for the production of aflatoxin (AF) B and G and other toxic metabolites, like cyclopiazonic acid (CPA). They are saprophytic soil dwellers and also become crop opportunistic epiphytes. The consequence is contamination of the crop with mycotoxins, such as carcinogenic AF. We investigated the Flavi community structure of maize and that of their surrounding soil, including their mycotoxigenicity. Furthermore, we investigated the link of the maize Flavi diversity with preharvest maize AF levels. The study was carried out in four selected districts of Zambia, in a low rainfall zone. The Flavi characterisation was triphasic, involving morphological (colony colour and sclerotia formation), metabolic (AF and CPA production) and genetic (calmodulin gene polymorphism) analyses. Flavi abundance was determined by dilution plate technique on modified rose Bengal agar. Results showed that Flavi communities on maize and in soil differed. Maize had a higher Flavi species diversity than soil. A. parasiticus dominated the soil community by frequency of field appearance (85%), while maize was dominated by A. minisclerotigenes (45%). CPA-producers with or without AF production dominated the maize (65%) while producers of only AF (B/G) dominated the soil (88%). The ratio between maize A. parasiticus and A. minisclerotigenes abundance seemed to have had a bearing on the levels of AF in maize, with a ratio close to 1:1 having higher levels than a pure community of either A. parasiticus or A. minisclerotigenes.

Niche partitioning association of fungal genera correlated with lower Fusarium and fumonisin-B1 levels in maize

Through partitioning of ecological niches, several fungi are able to coexist on the same host crop. In (partial) absence of niche partitioning, competitive exclusion among fungi can occur. Competitive exclusion is one of the bases for biocontrol. We investigated fungal correlations, in terms of relative abundance of the fungi, in pre-harvest maize, as a natural ecosystem model. Internal mycobiome fungal relative abundance of maize was used to establish correlations. The maize had been harvested from dry and wet agro-ecological zones of Zambia. The relative abundances of the fungal genera were determined using DNA amplicon sequencing. For this study, positive or absence of correlations between fungal genera signified good niche partitioning (co-existence), whereas negative correlations signified poor niche partitioning and potential for competitive exclusion. When species compete within one niche (competitive exclusion), we may expect to detect higher levels of mycotoxins—since mycotoxins are considered antagonistic agents aimed at defending or invading an ecological niche. To estimate the importance of mycotoxins in competitive exclusion, we measured the influence of the fungal correlations on levels of fumonisin-B1 (FB1) in the maize. FB1 data were derived from a previous study on the maize, determined by HPLC. Results showed that Sarocladium and Stenocarpella had the strongest significant negative correlation with Fusarium, suggesting poor niche partitioning and potential for antagonism of these genera with Fusarium. Furthermore, higher levels of Stenocarpella resonated with lower levels of FB1 and vice versa. It was also observed that, when Sarocladium was in low abundance (< 10%), the frequency of detection of higher levels of FB1 (> 100 µg kg−1) in the pre-harvest maize was highest.

Preharvest Maize Fungal Microbiome and Mycotoxin Contamination: Case of Zambia's Different Rainfall Patterns.

The preharvest maize mycobiome may be crucial in defining the health of the crop in terms of potential disease burden and mycotoxins. We investigated the preharvest maize mycobiome structure, including the influence of weather patterns, in terms of rainfall intensity, on its composition. In addition, we investigated correlation of genera Fusarium and Aspergillus with maize fumonisin-B1 and aflatoxin. Forty maize fields from selected districts in the wetter northern (N) and drier southern (S) agroecological zones of Zambia were sampled twice over two seasons (1 and 2). The defined weather variables over the two seasons were low rainfall with dry spell (S1), low rainfall (S2), and high rainfall (N1 and N2). High-throughput DNA amplicon sequencing of internal transcribed spacer 1 (ITS1) was used to determine the mycobiome structure and the composition in relation to rainfall patterns. We detected 61 genera, with Fusarium and previously unreported Sarocladium in Zambia to have the highest frequency of detection on the maize. There was a significant difference in fungal genera composition between S1 and S2 but no difference between N1 and N2. The weather pattern with dry spell, S1, had a strong proliferation of Meyerozyma and xerophiles Penicillium, Kodamaea, and Aspergillus. The four genera drove the difference in composition between S1 and S2 and the significantly higher fungal diversity in S1 compared to N2. Of the mycotoxin-important fungi, dry conditions (S1) were a key driver for proliferation of Aspergillus, while Fusarium proliferation occurred irrespective of weather patterns. The relative abundance of Aspergillus and Fusarium resonated with maize aflatoxin and fumonisin-B1 levels, respectively. IMPORTANCE Fungi contaminate various crops worldwide. Maize, an important human staple and livestock cereal, is susceptible to contamination with fungi in the field. Fungi are drivers of plant disease and can compromise yield. Some species of fungi are known to produce chemical compounds (mycotoxins), which are cancer-causing agents in humans and impair livestock productivity. It is important to understand the spectrum of fungi on maize and how weather conditions can impact their abundance. This is because the abundance of fungi in the field can have a bearing on the health of the crop as well as potential for mycotoxins contamination. By understanding the spectrum of the preharvest fungi, it becomes possible to know the key fungi adapted to the maize and subsequently the potential for crop disease as well as mycotoxins contamination. The influence of weather conditions on the spectrum of preharvest fungi on maize has not been fully explored.

Effect of Selected Fungicides in the Control of Aflatoxin-producing Fungi in Pre-harvest Maize (Zea mays L) in Anambra State

Contamination of maize by toxigenic fungi is the process that occur yet in the field. Aflatoxin contamination in several foodstuffs has been a recurrent problem. This study is aimed to evaluate the effect of selected fungicides in the control of aflatoxin-producing fungi affecting growth in pre-harvest maize (Zea mays L). Maize seeds treated with organic and synthetic fungicides were sown immediately after land preparation comprising of 13 plots. Five plants each were randomly selected from 13 plots for collecting data for 12 weeks at 2 week interval. Effect of organic and synthetic fungicide in the control of aflatoxin production on the growth parameters of maize showed that maize treated with Azadirachta indica recorded significant growth in the leaf area for all treatments for weeks 8, 10 and 12 while at week 6, maize treated with Cymbopogon citratus showed significant growth in the leaf area at 0.05% for TLg25%, TLg75% and TLg100%. Maize treated with synthetic fungicide (mancozeeb) showed significant growth in the leaf area for weeks 8, 10, 12 in all treatments. Maize treated with Azadirachta indica recorded a significant difference in the plant height for week 4, 10 and 12 in all treatments. For maize treated with Cympobogon citratus, weeks 2 and 8 recorded no significant difference in the plant height but showed a significant growth in the plant height at weeks 4 and 12 (for all treatments) while weeks 6 and 10 recorded significant growth in the plant height for some of the treatments. Maize treated with synthetic fungicide showed significant growth in the plant height for weeks 4, 10 and 12. Fungal isolates identified in this study were: Aspergillus spp. Fusarium spp. and Penicillium spp., with Aspergillus spp. having the highest frequency of occurrence of 4 in treatments TAi100%, TLg75%. The result showed that both organic and synthetic fungicide were effective in the control of aflatoxin-producing fungi on the maize yield but was more effective with the organic fungicide. The use of Azadirachta indica and Cymbopogon citratus is recommended as a means of biofungicides to control aflatoxin-producing fungi in maize.

Mapping Quantitative Trait Loci Associated With Resistance to Aflatoxin Accumulation in Maize Inbred Mp719.

Aflatoxins are carcinogenic and toxic compounds produced principally by fungal species Aspergillus flavus (Link: Fries) and A. parasiticus (Speare), which are common contaminants of food and feed. Aflatoxins can be found at dangerously high levels and can readily contaminate pre-harvest maize (Zea mays L.) grain. Sources of resistance to aflatoxin accumulation in maize have been identified, however, the highly quantitative nature and complex inheritance of this trait have limited the introgression of aflatoxin accumulation resistance into agronomically desirable lines. Mapping of quantitative trait loci (QTL) was performed on a bi-parental population comprised of 241 F2:3 families derived from the cross of inbred lines Mp705 (susceptible) × Mp719 (resistant). The mapping population was phenotyped in replicated field trials in three environments for resistance to aflatoxin accumulation under artificial inoculation with an A. flavus spore suspension. The genetic linkage map was constructed with 1,276 single nucleotide polymorphism (SNP) and simple sequence repeat (SSR) molecular markers covering a total genetic distance of 1,642 cM across all ten maize chromosomes. Multiple interval mapping revealed that majority of the aflatoxin-reducing alleles and the source for the larger effect QTL identified in this study were contributed from Mp719, the resistant parent. Two QTL identified on chromosome 1 (bin 1.06–1.07) and chromosome 3 (bin 3.09) were the most stable across different environments and when combined, explained 24.6% of the total phenotypic variance across all three environments. Results from the study showed that these chromosomal regions harbor important QTL for influencing aflatoxin accumulation, which is consistent with previous reports with other different mapping populations. These stable QTL were the most promising for controlling aflatoxin accumulation in maize grain. Identifying beneficial alleles derived from Mp719 and closely linked molecular markers through QTL analysis for implementation of MAS could accelerate breeding efforts to reduce aflatoxin accumulation in maize.

Aflatoxin-producing fungi associated with pre-harvest maize contamination in Uganda

Maize is an important staple crop for the majority of the population in Uganda. However, in tropical and subtropical climates, maize is frequently contaminated with aflatoxins, a group of cancer-causing and immuno-suppressive mycotoxins produced by Aspergillus section Flavi fungi. In Uganda, there is limited knowledge about the causal agents of aflatoxin contamination. The current study determined both the aflatoxin levels in pre-harvest maize across Uganda and the structures of communities of aflatoxin-producing fungi associated with the maize. A total of 256 pre-harvest maize samples were collected from 23 major maize-growing districts in eight agro-ecological zones (AEZ). Maize aflatoxin content ranged from 0 to 3760 ng/g although only around 5% for Ugandan thresholds. For EU it is about 16% of the samples contained aflatoxin concentrations above tolerance thresholds. A total of 3105 Aspergillus section Flavi isolates were recovered and these were dominated by the A. flavus L morphotype (89.4%). Densities of aflatoxin-producing fungi were negatively correlated with elevation. Farming systems and climatic conditions of the AEZ are thought to have influenced communities' structure composition. Fungi from different AEZ varied significantly in aflatoxin-producing abilities and several atoxigenic genotypes were identified. The extremely high aflatoxin concentrations detected in some of the studied regions indicate that management strategies should be urgently designed for use at the pre-harvest stage. Atoxigenic genotypes detected across Uganda could serve as aflatoxin biocontrol agents to reduce crop contamination from fields conditions and throughout the maize value chain.

Occurrence of Mycotoxigenic Fusarium Species and Competitive Fungi on Preharvest Maize Ear Rot in Poland.

Maize has become one of the most important crops for food and feed production—both as a silage and crop residue worldwide. The present study aimed to identify the co-occurrence of Fusarium subglutinans, Fusarium verticillioides, Trichoderma atroviride, Sarocladium zeae, and Lecanicillium lecanii on maize ear rot. Further, the accumulation of mycotoxins as secondary metabolites of Fusarium spp. in maize ear samples was also analyzed. Maize ear samples were collected between 2014 and 2017 from two main maize growing areas in Poland (Greater Poland and Silesia region). A significant difference was found in the frequency of two main Fusarium spp. that infect maize ears, namely F. subglutinans and F. verticillioides. In addition to Fusarium spp. T. atroviride, S. zeae, and L. lecanii were also identified. T. atroviride species was found in 14% of maize samples examined between 2014 and 2017, particularly with a high percentage of Trichoderma spp. recorded in 2014, i.e., in 31% of samples. However, mycotoxin content (beauvericin and fumonisins) varied, depending on both the location and year of sampling. The interaction of fungi and insects inhabiting maize ear and kernel is very complex and not yet elucidated. Therefore, further research is required in this area.

Estimation of Maize grain yield using multispectral satellite data sets (SPOT 5) and the random forest algorithm

Crop yield estimation is a very important aspect in food production as it provides information to policy and decision makers that can guide food supply not only to a nation but also influence its import and export dynamics. Remote sensing has the ability to provide the given tool for crop yield predictions before harvesting. This study utilised canopy reflectance from a multispectral sensor to develop vegetation indices that serve as input variables into an empirical pre-harvest maize (Zea mays) yield prediction model in the north eastern section in Free State province of South Africa. Some fields in this region that were grown of maize under rain-fed conditions were monitored and the grain harvested after 7-8 months with actual yields measured. The acquisition of suitable medium resolution SPOT 5 images over this area was in March and June before the grains were harvested in July of 2014. A number of well known spectral indices were developed using the visible and near infrared bands. Through the random forest algorithm predictive models, maize grain yields were estimated successfully from the March images. The accuracies of these models were of an R2 of 0.92 (RMSEP = 0.11, MBE = -0.08) for the Agnes field and for Cairo the R2 was 0.9 (RMSEP = 0.03, MBE = 0.004). These results were produced by the SAVI and NDVI respectively for both fields. It was therefore evident that the predictive model applied in this study was site specific and would be interesting to be tested for an optimal period during the plant life cycle to predict grain yields of maize in South Africa.Keywords: maize, non-linear regressions, prediction, random forest, spectral indices, SPOT 5, variable importance, yield

Fumonisins and Related Fusarium Species in Pre-harvest Maize Ear Rot in Poland

Two Fusarium species were identified in mouldy maize ears with the highest frequency during 2005–2014 in 7 seasons: F. subglutinans (3.1–42.0%) and F. verticillioides (44.1– 70.3%). Two other species were also found but with lower frequency: F. graminearum (1.0–13.0%) and F. poae (1–45.7%). In 2005 fumonisin FB1, and in 2013 and 2014 three fumonisins (FBs) – FB1, FB2 and FB3 – were identified in harvest samples. The Fusarium-damaged kernel (FDK) fraction contained almost the totality of mycotoxins (90.0–95.0%), while healthy looking kernels (HLK) contained only below 5.0 to 10.0%. Kernels naturally infected by F. verticillioides and F. proliferatum contained (in mg kg−1) up to 710.00 of fumonisin B1, up to 209.72 of fumonisin B2 and up to 35.72 of fumonisin B3.

Fungal screening and aflatoxin production by Aspergillus section Flavi isolated from pre-harvest maize ears grown in two Argentine regions

Aflatoxin contamination in maize kernels grown in central Argentina has increased since 2008. Pre-harvest maize ear samples were collected during two growing seasons to determine prevalent fungal genera as well as aflatoxin production capacity by Aspergillus sect. Flavi in two maize regions. A direct planting procedure was performed for fungal screening. Aspergillus section Flavi was identified via a morphological analysis and some colonies were isolated. Strains were subjected to molecular analysis and aflatoxin production was studied. Fusarium was the fungus genus with the highest severity, followed by Penicillium and Aspergillus in both regions. Aspergillus sect. flavi were detected in 27 (73%) samples. PCR amplifications were observed in 94% of the isolates. Aspergillus sect. flavi severity varied significantly between years. A great proportion of toxigenic strains were observed in a native Aspergillus sect. flavi population (95%) producing B- and G-type aflatoxins. Maize ears grown in regions I and IV in Argentina are prone to degradation by fungi. Toxigenic strains are predominant in native Aspergillus sect. Flavi populations. Aflatoxin contamination of maize kernels is not restricted to post-harvest; rather, it is a serious issue that begins with colonization by Aspergillus sect. Flavi in ears.

Mycotoxins and related Fusarium species in preharvest maize ear rot in Poland

This work presents a survey on mycotoxins (seasons 2013 and 2014) and Fusarium species (seasons from 1985 to 2014) in maize ear rot in Poland. Twelve mycotoxins were identified in maize kernel samples exhibiting symptoms of Fusarium ear rot or rotten kernels at the harvest in two locations in Poland during the seasons 2013 and 2014. This is the first complex survey on the co-occurrence of four Fusarium mycotoxin groups in maize kernels: the group of the mycohormone zearalenone; the group of trichothecenes – deoxynivalenol and nivalenol; the group of fumonisins; and the group of cyclic hexadepsipeptides – beauvericin and enniatins; and in addition, moniliformin. Four Fusarium species were identified in preharvest maize ear rot in the 2013 and 2014 harvests namely:&lt;br /&gt; F. graminearum, F. poae, F. subglutinans and F. verticillioides. Since 1985, eleven Fusarium species have been identified in 13 investigation seasons. Apart from those mentioned above, F. avenaceum, F. cerealis, F. culmorum and&lt;br /&gt; F. sporotrichioides were observed with irregular frequencies, and three species, i.e. F. proliferatum, F. tricinctum and F. equiseti, were identified sporadically. A significant increase of F. verticillioides frequency and a decrease of F. subglutinans frequency and changes of mycotoxin profile have been observed in the two decades since 1995.

A survey of pre-harvest ear rot diseases of maize and associated mycotoxins in south and central Zambia

Maize ear rots reduce grain yield and quality with implication on food security and health. Some of the pathogenic fungi produce mycotoxins in maize grain posing a health risk to humans and livestock. Unfortunately, the levels of ear rot and mycotoxin infection in grain produced by subsistence farmers in sub-Saharan countries are not known. A survey was thus conducted to determine the prevalence of the ear rot problem and levels of mycotoxins in maize grain. A total of 114 farmsteads were randomly sampled from 11 districts in Lusaka and southern provinces in Zambia during 2006. Ten randomly picked cobs were examined per farmstead and the ear rot disease incidence and severity were estimated on site. This was followed by the standard seed health testing procedures for fungal isolation in the laboratory. Results indicated that the dominant ear rots were caused by Fusarium and Stenocarpella. Incidence of Fusarium verticillioides ranged from 2 to 21%, whereas that of Stenocarpella maydis reached 37% on ear rot diseased maize grain. In addition, 2–7% F. verticillioides, and 3–18% Aspergillus flavus, respectively, were recovered from seemingly healthy maize grain. The mean rank of fungal species, from highest to lowest, was F. verticillioides, S. maydis, A. flavus, Fusarium graminearum, Aspergillus niger, Penicillium spp., Botrydiplodia spp., and Cladosporium spp. The direct competitive ELISA-test indicated higher levels of fumonisins than aflatoxins in pre-harvest maize grain samples. The concentration of fumonisins from six districts, and aflatoxin from two districts, was 10-fold higher than 2 ppm and far higher than 2 ppb maximum daily intake recommended by the FAO/WHO. The study therefore suggested that subsistence farmers and consumers in this part of Zambia, and maybe also in similar environments in sub-Saharan Africa, might be exposed to dangerous levels of mycotoxins due to the high levels of ear rot infections in maize grain.

Delivery systems for biological control agents to manage aflatoxin contamination of pre-harvest maize

While soil application of a competitive non-toxigenic Aspergillus flavus strains is successful in reducing aflatoxin contamination in certain crops, direct application to aerial reproductive structures could be more effective for maize. A sprayable, clay-based water-dispersible granule formulation was developed to deliver non-toxigenic A. flavus strain K49 directly to maize ears. The efficacy of the K49 water-dispersible granule in mitigating aflatoxin in maize (Zea mays L.) was evaluated. Field studies were conducted to compare K49 colonization and effectiveness in reducing aflatoxin contamination when applied either as a soil inoculant or as a directed spray in plots infested with toxigenic strain F3W4. Fifty percent of non-toxigenic A. flavus was recovered from non-treated controls and from plots soil inoculated with K49 on wheat. In spray treatments with formulated or unformulated K49 conidia, over 90% of A. flavus recovered was non-toxigenic. Soil-applied K49 reduced aflatoxin contamination by 65% and spray applications reduced contamination by 97%. These findings suggest direct spray application of non-toxigenic A. flavus strains may be better than soil inoculation at controlling maize aflatoxin contamination and that a water-dispersible granule is a viable delivery system for maintaining viability and efficacy of the biological control agent, K49.

Occurrence of Toxic Hexadepsipeptides in Preharvest Maize Ear Rot Infected by Fusarium poae in Poland

AbstractTwenty‐seven preharvest maize ears affected by Fusarium poae rot (disease score 36–100%) were selected in 1998 and 1999 in Poland and examined for the occurrence of toxic hexadepsipeptides: beauvericin (BEA), enniatin A, enniatin B and enniatin B1. The identification of F. poae was confirmed by sequence analysis of variable internal transcribed spacer regions and compared with NCBI gene bank DNA sequences. Chemical analyses were performed by HPLC‐MS. In 27 ears infected by F. poae were detected: BEA (trace to 46 μg/g) in 18 samples, enniatin A (trace to 37 μg/g) in nine samples, enniatin B (trace to 47 μg/g) in 15 samples and enniatin B1 (trace to 25 μg/g) in 12 samples. When 20 strains of F. poae isolated from these samples were cultured on rice, all produced BEA (1.9–75 μg/g), three enniatin A (1.8–2 μg/g), 12 enniatin B (1.1–5.1 μg/g) and eight enniatin B1 (1.2–5.2 μg/g). Occurrence and quantification of enniatin A, enniatin B and enniatin B1 and their co‐occurrence with BEA in maize kernels is reported for the first time.

Screening of Local &lt;i&gt;Bacillus thuringiensis&lt;/i&gt; Isolates for Toxicity to &lt;i&gt;Chilo partellus, Sesamia calamistis&lt;/i&gt; and &lt;i&gt;Busseola fusca&lt;/i&gt; in Kenya

Stem borers are a major source of pre-harvest maize crop losses in Kenya and many Sub- Saharan African countries. This menace needs to be addressed if food security is to be realized in this region. Seven local isolates of Bacillus thuringiensis (Bt) strains were isolated from soils collected from Kakamega and Machakos districts in Kenya. They were screened for toxicity against 1st and 2nd instar larvae of Chilo partellus, Sesamia calamistis and Busseola fusca through laboratory bioassays on artificial and natural diets. On farm Bt toxin potency trials were carried out only in Machakos using isolate 1M which was isolated from the area. The various isolates showed differences in their toxicity to the three stem borers. Isolates 1M and VM-10 (from Machakos district) were found to be the most potent against C. partellus with larval mortalities of 100 % within 72 h. Their LD50 values were 0.004 mg/ml and 0.04 mg/ml respectively. The most toxic isolates against S. calamistis were, 44M, VM-10 and 1M, with larval mortalities of 73%, 64% and 62% respectively after 72h at a concentration of 8.6 mg/ml through artificial diet bioassays on 1st instar larvae. Isolates 44M and K10-2 showed high toxicity against B. fusca with larval mortalities of 20% by artificial diet bioassays and 44% by maize leaf bioassays respectively. Leaf disk bioassays with all the insect species showed higher larval mortalities than those done with the artificial diet bioassays indicating the larval preference of natural diet. However leaf disk bioassays with B. fusca recorded higher larval mortalities with sorghum than maize leaves. Field trial results obtained from Machakos district using a biopesticide made from isolate 1M indicated that it was highly effective in stem borer control. Keywords: Bacillus thuringiensis; bioassays; B. fusca; C. partellus; S. calamistis; insect larvae; mortality; toxicity. J. Trop. Microbiol. Biotechnol. Vol. 3 (2) 2007: pp. 27-35

Soil fungal population in preharvest maize ecosystem in different tillage practices in Argentina

The distribution of the soil borne fungal population in maize non-rhizospheric soil in experimental trials were studied during the harvest seasons 2000/2001 and 2001/2002. The effect of different tillage practices was evaluated. Soil samples were collected from three tillage treatments, conventional tillage, reduced tillage and no tillage, with and without grazing. The distribution of fungal propagules in different treatments was compared. Soil samples were collected from the top soil (3 cm) before planting, in the sprong. No tillage without grazing and reduced tillage with grazing had the highest densities of filamentous fungi (5.71 and 5.85 log, respectively). The mycological survey showed the presence of six genera of filamentous fungi. They were Aspergillus, Fusarium, Penicillium, Trichoderma, Cladosporium, Alternaria. The species identified from genus Aspergillus were A. flavus, A. restrictus, A. candidus, A. parasiticus and other Aspergillus spp. The species identified from genus Penicillium were P. pinophylum, P. citreonigrum, P. implicatum, P. purpurogenum, P. minioluteum, P. waksmanii, P. restrictum, P. rugulosum, P. funiculosum and P. variabile. Species from genus Fusarium were identified as F. verticillioides, F. oxysporum, F. proliferatum and others Fusarium species. The isolation frequency of Aspergillus increased in the no tillage and grazing practices treatments. The data indicate that different agricultural practices impact soil inocula of principal maize toxigenic fungi in the production area. To our knowledge, this is the first report on the effect of tillage management practices on fungal populations in preharvest maize agroecosystem in Argentina.

A protective endophyte of maize: Acremonium zeae antibiotics inhibitory to Aspergillus flavus and Fusarium verticillioides

The maize endophyte Acremonium zeae is antagonistic to kernel rotting and mycotoxin producing fungi Aspergillus flavus and Fusarium verticillioides in cultural tests for antagonism, and interferes with A. flavus infection and aflatoxin contamination of preharvest maize kernels. Chemical studies of an organic extract from maize kernel fermentations of Acremonium zeae (NRRL 13540), which displayed significant antifungal activity against Aspergillus flavus and F. verticillioides, revealed that the metabolites accounting for this activity were two newly reported antibiotics pyrrocidines A and B. Pyrrocidines were detected in fermentation extracts for 12 NRRL cultures of Acremonium zeae isolated from maize kernels harvested in Illinois (4/4 cultures), North Carolina (5/5), Georgia (1/2) and unrecorded locations within the USA (2/2). Pyrrocidine B was detected by LCMSMS in whole symptomatic maize kernels removed at harvest from ears of a commercial hybrid that were wound-inoculated in the milk stage with A. zeae (NRRL 13540) or (NRRL 13541). The pyrrocidines were first reported from the fermentation broth of an unidentified filamentous fungus LL-Cyan426, isolated from a mixed Douglas Fir hardwood forest on Crane Island Preserve, Washington, in 1993. Pyrrocidine A exhibited potent activity against most Gram-positive bacteria, including drug-resistant strains, and was also active against the yeast Candida albicans. In an evaluation of cultural antagonism between 13 isolates of A. zeae in pairings with A. flavus (NRRL 6541) and F. verticillioides (NRRL 25457), A. zeae (NRRL 6415) and (NRRL 34556) produced the strongest reaction, inhibiting both organisms at a distance while continuing to grow through the resulting clear zone at an unchanged rate. Maximum colony diameters for A. zeae (NRRL 6415) and (NRRL 13540), on potato dextrose agar after 14 d, were attained within the range of 25-30 degrees C, with less growth recorded at 15 degrees and 37.5 degrees and no growth at 5 degrees. Potential interactions between A. zeae and other maize endophytes are considered and the significance of these interactions relative to the aflatoxin and fumonisin contamination of preharvest maize is presented. This is the first report of natural products from Acremonium zeae.

Natural occurrence of Fusarium and subsequent fumonisin contamination in preharvest and stored maize in Benin, West Africa

The natural occurrence of Fusarium and fumonisin contamination was evaluated from 1999 to 2003 in both preharvest and stored maize produced by small-scale farmers in four agroecological zones of Benin. Mycological analyses revealed a predominance of both Fusarium and Aspergillus in maize samples compared to other genera. The two Fusarium species most commonly isolated from maize were Fusarium verticillioides (68%) and Fusarium proliferatum (31%). Atypical isolates of F. verticillioides with some characteristics of Fusarium andiyazi but apparently closer to F. verticillioides, because the isolates were all high fumonisin producers, were also found only on preharvest maize. Study of F. verticillioides strains showed the presence of extremely high fumonisin producers in Benin with total fumonisin levels ranging from 8240 to 16,690 mg/kg. Apart from 2002–2003, Fusarium occurrence was not significantly different from one zone to another, although a slight decrease was observed from south, humid, to north, drier. Fusarium occurrence varied somewhat from one season to another. It significantly decreased over the 6 months of storage. Widespread fumonisin occurrence in maize was observed. Most of the maize samples collected were found positive for fumonisin with levels ranging from not detected to 12 mg/kg in 1999–2000, 6.7 mg/kg in 2000–2001 and 6.1 mg/kg in 2002–2003. Fumonisin levels in maize were found to be significantly higher in the two southern zones during all the surveys. The highest mean total fumonisin level was detected in 1999–2000 in maize samples from the southern Guinea Savannah (SGS) (12 mg/kg), whereas in both 2000–2001 and 2002–2003, it was in samples from the forest mosaic savannah (FMS) (6.7 and 6.1 mg/kg, respectively). Fumonisin levels varied from one season to another and, throughout the storage time, showing a decreasing trend in each zone. However, this decrease was not significant every season. An increasing trend was observed during some seasons in the SGS and northern Guinea Savannah (NGS) zones. The results of this study emphasise that farmers and consumers, not only in Benin but also in other West African countries, should be alerted to the danger of fumonisin contamination in maize.

Occurrence of aflatoxins and fumonisins in preharvest maize from south-western Nigeria

A survey was conducted on the incidence of fungi, and the natural occurrence of aflatoxins and fumonisins in preharvest maize from fields in south-western Nigeria. Mycological examinations revealed the predominance of F. verticillioides (Zea mays) (syn. F. moniliforme), occurring in 89.3% of samples with a mean kernel infection of 49.4%, while Aspergillus flavus was isolated from 65% of samples having a mean kernel infection of 6.8%. Aflatoxin B1 was detected in 18.4% of samples with a mean of 22 μg kg−1, while aflatoxins B2, G1 and G2 were present in 7.8, 2.9 and 1% of the samples with mean levels of 10, 8 and 7 μg kg−1, respectively, in contaminated samples. Total aflatoxins ranged from 3 to 138 μg kg−1 in positive samples, with a mean of 28 μg kg−1. Fumonsin B1 was the predominant toxin detected in terms of frequency (78.6% of samples) and quantity (concentration range 70–1780 μg kg−1, mean = 495 μg kg−1). Fumonisin B2 was detected in 68 samples (66%) with a mean of 114 μg kg−1. Fifteen samples were contaminated with both aflatoxins and fumonisins.