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1.
Aflatoxin contamination resulting from maize infection by Aspergillus flavus is both an economic and a public health concern. Therefore, strategies for controlling aflatoxin contamination in maize are being investigated. The abilities of eleven naturally occurring atoxigenic isolates in Nigeria to reduce aflatoxin contamination in maize were evaluated in grain competition experiments and in field studies during the 2005 and 2006 growing seasons. Treatments consisted of inoculation of either grains in vials or ears at mid-silking stage in field plots, with the toxigenic isolate (La3228) or atoxigenic isolate alone and co-inoculation of each atoxigenic isolate and La3328. Aflatoxin B1?+?B2 concentrations were significantly (p?<?0.05) lower in the co-inoculation treatments compared with the treatment in which the aflatoxin-producing isolate La3228 was inoculated alone. Relative levels of aflatoxin B1?+?B2 reduction ranged from 70.1% to 99.9%. Among the atoxigenics, two isolates from Lafia, La3279 and La3303, were most effective at reducing aflatoxin B1?+?B2 concentrations in both laboratory and field trials. These two isolates have potential value as agents for the biocontrol of aflatoxin contamination in maize. Because these isolates are endemic to West Africa, they are both more likely than introduced isolates to be well adapted to West African environments and to meet regulatory concerns over their use throughout that region.  相似文献   

2.
不产毒黄曲霉菌对产毒黄曲霉菌产毒抑制效果分析   总被引:1,自引:0,他引:1       下载免费PDF全文
本实验6株菌分离自广东、山东、辽宁和湖北四省的花生土壤中,通过形态学和分子生物学鉴定均为黄曲霉菌,HPLC测定其产毒能力,其中GZ-6为产毒菌,GZ-15、WF-5、WF-20、JZ-2和YC-8为不产毒菌。分别以花生和玉米为培养基,将不产毒黄曲霉菌和产毒菌(孢子浓度:104:105或105:105)进行混合培养,测定不产毒菌对产毒黄曲霉产毒的抑制效果。结果显示:不产毒菌对产毒菌产毒的抑制率随着其孢子浓度的增加而明显加强,当孢子浓度比为105:105(不产毒菌:产毒菌)时,5株不产毒菌在玉米培养基上对产毒菌产毒的抑制率为34.55%~75.94%,在花生培养基上对产毒菌产毒的抑制率为38.03%~83.03%,其中WF-5、WF-20和GZ-15这三株不产毒菌对产毒黄曲霉产毒的抑制效果均达到75.00%以上,可以作为田间防治黄曲霉毒素污染的候选菌株。  相似文献   

3.
Aflatoxins are a family of highly toxic and carcinogenic toxins produced by several Aspergillus species. Aflatoxin contamination of agricultural commodities both pre- and postharvest is a serious food safety issue and a significant economic concern. Using nonaflatoxigenic A. flavus isolates to competitively exclude toxigenic A. flavus isolates in agricultural fields has become an adopted approach to reduce aflatoxin contamination. From screening subgroups of nonaflatoxigenic A. flavus, we identified an A. flavus isolate, TX9-8, which competed well with three A. flavus isolates producing low, intermediate, and high levels of aflatoxins, respectively. TX9-8 has a defective polyketide synthase gene (pksA), which is necessary for aflatoxin biosynthesis. Co-inoculating TX9-8 at the same time with large sclerotial (L strain) A. flavus isolates at a ratio of 1:1 or 1:10 (TX9-8:toxigenic) prevented aflatoxin accumulation. The intervention of TX9-8 on small sclerotial (S strain) A. flavus isolates varied and depended on isolate and ratio of co-inoculation. At a ratio of 1:1 TX9-8 prevented aflatoxin accumulation by A. flavus CA28 and reduced aflatoxin accumulation 10-fold by A. flavus CA43. No decrease in aflatoxin accumulation was apparent when TX9-8 was inoculated 24 h after toxigenic L- or S strain A. flavus isolates started growing. The competitive effect likely is due to TX9-8 outgrowing toxigenic A. flavus isolates.  相似文献   

4.
Aflatoxins are highly toxic carcinogens produced by several species in Aspergillus section Flavi. Strains of A. flavus that do not produce aflatoxins, called atoxigenic strains, have been used commercially in North America as tools for limiting aflatoxin contamination. A similar aflatoxin management strategy is being pursued in Nigeria. In the current study, loci across the 68 kb aflatoxin biosynthesis gene cluster were compared among 18 atoxigenic and two aflatoxin-producing vegetative compatibility groups (VCGs) from Nigeria and an atoxigenic VCG used commercially in North America. Five of the atoxigenic VCGs had large deletions (37–65 kb) extending from the teleomeric side of the aflatoxin biosynthesis cluster. In one VCG (AV0222) the deletion extended through the cluster to the adjacent sugar cluster. The remaining twelve atoxigenic VCGs, including the VCG used for aflatoxin management in North America, contained all the aflatoxin pathway genes, but with defects. Two observations support the long-term persistence of atoxigenicity within A. flavus: first, a comparison of pathway genes revealed more changes in atoxigenic than in aflatoxin-producing isolates relative to the aflatoxin-producing strain NRRL 3357; and second, several non-synonymous changes are unique to atoxigenics. Atoxigenic VCG diversity was assessed with phylogenetic analyses. Although some atoxigenics share relatively recent ancestry, several are more closely related to aflatoxin producers than to other atoxigenics. The current study demonstrates VCGs of A. flavus in West Africa with diverse mechanisms of atoxigenicity and potential value in aflatoxin management programmes.  相似文献   

5.
Aspergillus flavus is the main etiological agent for aflatoxin contamination of crops. Its close relative, A. oryzae, does not produce aflatoxins and has been widely used to produce fermented foods. We compared the phylogeny of A. oryzae isolates and L- and S-type sclerotial isolates of A. flavus using single nucleotide polymorphisms in the omtA gene in the aflatoxin biosynthesis gene cluster and deletions in and distal to the norB-cypA intergenic region as phylogenetic signals. Aflatoxin-producing ability and sclerotial size also were weighted in the analysis. Like A. flavus, the A. oryzae isolates form a polyphyletic assemblage. A. oryzae isolates in one clade strikingly resemble an A. flavus subgroup of atoxigenic L-type isolates. All toxigenic S-type isolates closely resemble another subgroup of atoxigenic L-type isolates. Because atoxigenic S-type isolates are extremely rare, we hypothesize that loss of aflatoxin production in S-type isolates may occur concomitantly with a change to L-type sclerotia. All toxigenic L-type isolates, unlike A. oryzae, have a 1.0 kb deletion in the norB-cypA region. Although A. oryzae isolates, like S-type, have a 1.5 kb deletion in the norB-cypA region, none were cladally related to S-type A. flavus isolates. Our results show that A. flavus populations are genetically diverse. A. oryzae isolates may descend from certain atoxigenic L-type A. flavus isolates.  相似文献   

6.
Seven truck-loads of maize were tested for mycotoxin contamination. Aflatoxin was identified in all 7 at concentrations from 3 ng/g-501 ng/g (aflatoxin B1+ B2). Cyclopiazonic acid was identified in 4 loads with concentrations from 25-250 ng/g. Deoxynivalenol was found in 4 of 5 loads tested, over a range of 46-676 ng/g. Ninteeen isolates of Aspergillus flavus from the samples were tested for ability to accumulate cyclopiazonic acid and aflatoxin in liquid culture. Fourteen produced cyclopiazonic acid (0.5-135 μg/mL), 12 produced aflatoxin (0.01-0.70 μg/mL, aflatoxin B1+ B2), and one aflatoxin-producing isolate did not produce cyclopiazonic acid.  相似文献   

7.
Aflatoxin B(1) is a toxigenic and carcinogenic compound produced by Aspergillus flavus and Aspergillus parasiticus. To inhibit aflatoxin contamination of peanuts, seeds of two peanut breeds, IAC Caiapó and IAC Runner 886, were inoculated with A. parasiticus (1.0 × 10(6) spores per ml) and the yeast Saccharomyces cerevisiae (3.2 × 10(7) cells per ml) and incubated at 25°C for 7 and 15 days. Two experiments were conducted for each incubation period separately. The treatments were completely randomized, with three replications per treatment. Treatments included the two cultivars and three types of inoculation (pathogen alone, yeast and pathogen, and yeast 3 h before pathogen). Aflatoxin B(1) was quantified with a densitometer at 366 nm after thin layer chromatography. Aflatoxin B(1) contamination in peanuts was reduced after the addition of S. cerevisiae. The concentration of aflatoxin B(1) decreased by 74.4 and 55.9% after 7 and 15 days, respectively. The greatest aflatoxin reduction was observed when S. cerevisiae was inoculated 3 h before the pathogen in IAC Caiapó seeds and incubated for 7 days at 25°C. The use of S. cerevisiae is a promising strategy for biological control of aflatoxin contamination in peanuts.  相似文献   

8.
Biocontrol by competitive inhibition using atoxigenic Aspergillus flavus strains has been shown to be an effective method for controlling aflatoxin production in peanuts, maize and cottonseed. Selecting biocontrol strains is not straightforward, as it is difficult to assess fitness for the task without expensive field trials. Reconstruction experiments have been generally performed under laboratory conditions to investigate the biological mechanisms underlying the efficacy of atoxigenic strains in preventing aflatoxin production and/or to give a preliminary indication of strain performance when released in the field. The study here described was conducted in order to evaluate the potential of the different atoxigenic A. flavus strains, colonizing the corn fields of the Po Valley, in reducing aflatoxin accumulation when grown in mixed cultures together with atoxigenic strains; additionally, we developed a simple and inexpensive procedure that may be used to scale-up the screening process and to increase knowledge on the mechanisms interfering with mycotoxin production during co-infection.  相似文献   

9.
Maize samples were collected during a survey in three agro-ecological zones in Nigeria to determine the distribution and aflatoxin-producing potential of members of Aspergillus section Flavi. The three agro-ecological zones were, Derived Savannah (DS) and Southern Guinea Savannah (SGS) in the humid south and North Guinea Savannah (NGS) in the drier north. Across agro-ecological zones, Aspergillus was the most predominant fungal genera identified followed by Fusarium with mean incidences of 70 and 24%, respectively. Among Aspergillus, A. flavus was the most predominant and L-strains constituted >90% of the species identified, while the frequency of the unnamed taxon S(BG) was <3%. The incidence of atoxigenic strains of A. flavus was higher in all the districts surveyed except in the Ogbomosho and Mokwa districts in DS and SGS zones, respectively, where frequency of toxigenic strains were significantly (P<0.05) higher than that of atoxigenic strains. The highest and lowest incidence of aflatoxin positive samples was recorded in the SGS (72%) and NGS (20%), respectively. Aflatoxin contamination in grain also followed a similar trend and the highest mean levels of B-aflatoxins were detected in maize samples obtained from Bida (612 ng g(-1)) and Mokwa (169 ng g(-1)) districts, respectively, in the SGS. Similarly, the highest concentrations of G-aflatoxins were detected in samples from Akwanga district in the SGS with a mean of 193 and 60 ng g(-1), respectively. When agro-ecological zones were compared, B-aflatoxins were significantly (P<0.05) higher in SGS than in NGS, and intermediate in maize samples from the DS agro-ecological zone.  相似文献   

10.
Aflatoxin contamination in three varieties of maize (Zea mays L), viz Diara composite, M9 and Suwan composite, under various cultivation rates and planting densities was examined during the 1987 and 1989 Kharif (monsoon) crops. Cultivation rates comprising single line weeding (SLW) with one spading, SLW with two spadings and SLW with three spadings did not have significant effects on aflatoxin production in the preharvest standing crop. Of the three planting populations, the toxin level was highest under 56000 plants ha?1 followed by 83000 plants ha?1, and 67000 plants ha?1 in Aspergillus flavus inoculated plots (I1) and uninoculated plots (I0), respectively. The variety M9 was most susceptible to A flavus infection and supported higher aflatoxin production under I1 condition. Aflatoxin concentration was lowest in Diara composite. Correlation analysis showed a positive and highly significant relation between A flavus incidence and aflatoxin contamination (r = +0.73, P < 0.01).  相似文献   

11.
Maize is a major staple crop and calorie source for many people living in Sub-Saharan Africa. In this region, Aspergillus flavus causes ear rot in maize, contributing to food insecurity due to aflatoxin contamination. The biological control principle of competitive exclusion has been applied in both the United States and Africa to reduce aflatoxin levels in maize grain at harvest by introducing atoxigenic strains that out-compete toxigenic strains. The goal of this study was to determine if the efficacy of preharvest biocontrol treatments carry over into the postharvest drying period, the time between harvest and the point when grain moisture is safe for storage. In Sub-Sahara Africa, this period often is extended by weather and the complexities of postharvest drying practices. Maize grain was collected from fields in Texas and North Carolina that were treated with commercial biocontrol products and untreated control fields. To simulate moisture conditions similar to those experienced by farmers during drying in Sub-Sahara Africa, we adjusted the grain to 20% moisture content and incubated it at 28 °C for 6 days. Although the initial number of kernels infected by fungal species was high in most samples, less than 24% of kernels were infected with Aspergillus flavus and aflatoxin levels were low (<4 ppb). Both toxigenic and atoxigenic strains grew and spread through the grain over the incubation period, and aflatoxin levels increased, even in samples from biocontrol-treated fields. Our molecular analysis suggests that applied biocontrol strains from treated fields may have migrated to untreated fields. These results also indicate that the population of toxigenic A. flavus in the harvested grain will increase and produce aflatoxin during the drying period when moisture is high. Therefore, we conclude that preharvest biocontrol applications will not replace the need for better postharvest practices that reduce the drying time between harvest and storage.  相似文献   

12.
Aflatoxin contents in 12 types of herbal teas were determined by high performance liquid chromatography (HPLC) with fluorescence detector using immunoaffinity column clean-up. Forty eight samples were collected from four local herbal shops in Manisa, Turkey. Of the 48 samples analyzed, 43 were aflatoxin positive. The highest concentration of aflatoxin (34.18 µg/kg) was determined in a sample of camomile tea. The occurrence of AFB1, B2, G1 and G2 was found in samples at levels of 54, 29, 71 and 46 %, respectively. Aflatoxin B1, B2, G1 and G2 contamination levels varied from 0 to 14.2, 0 to 12.4, 0 to 13.5 and 0 to 28.7 µg/kg, respectively. Aflatoxin was not detected in five samples consisting of linseed, lime and fennel tea.  相似文献   

13.
Isobutyric acid (IBA) and propionic-acetic acid (PA) were applied to comparable 52.8 m3 lots of freshly harvested yellow dent maize containing 27% moisture. After 6 months storage, 30% Aspergillus flavus infection and low levels of aflatoxin were detected in adjacent bins of IBA-treated and PA-treated maize. Extensive samples were taken after 7 months from moldy spots in each bin and evaluated for aflatoxin, zearalenone, ochratoxin and microorganisms. Aspergillus flavus (106 propagules/g) was detected in 40% of the PA samples, but no aflatoxin was found. Also, counts of Aspergillus fumigatus, Absidia and Penicillia were high. In addition to the molds found on PA maize, Aspergillus niger was identified on IBA-treated maize. Aspergillus flavus (104–107 propagules/g) was present in 79% of the IBA samples; aflatoxin (from 2 to 857 ng/g) was detected in 57%. Aflatoxin contamination varied between locations within a moldy area. Among 20 individual kernels picked at random from each location, aflatoxin contamination ranged from 150 to 21.800 ng/g in positive kernels. Evidently, bulk quantities of maize must be appraised on the basis of individual kernels because toxin-free kernels often are adjacent to highly contaminated kernels.  相似文献   

14.
A follow-up study on the quality of maize for sale in West African public markets was carried out in Benin and Niger from August 15–28, 2013. Complementing the earlier study, this present assessment included not only retailers but also wholesalers and maize producers. Samples were evaluated for parameters related to the physical quality of the maize and for aflatoxin contamination. Most maize value chain actors process their offered grain using traditional methods for threshing, winnowing and drying. Maize for sale in the markets surveyed had an average moisture content ranging between 12 and 14%. Non-grain impurities amounted to 0–2.3% while mouldy grains ranged between 0.2 and 0.8%. The impurity level in grain was three times higher among wholesalers compared to retailers and producers. An insect pest, the Larger Grain Borer (Prostephanus truncatus (Horn) was found only in Benin but Sitophilus zeamais Motschulsky, Cryptolestes ferrugineus Stephens, and Tribolium castaneum Herbst, were present in maize for sale in the markets in of both countries. Insect pest frequency was 16 times higher in wholesalers' grain compared to that of retailers and producers. Aflatoxin levels exceeding the accepted standard of 20 ppb were noted in markets in both countries. The highest proportion of aflatoxin-contaminated maize was in wholesalers’ grain in Malanville market.  相似文献   

15.
Rotary International with the International Institute of Tropical Agriculture (IITA) conducted an information campaign from 2000 to 2004 to increase public awareness of aflatoxin in Benin, Ghana and Togo. Key informant interviews with 2416 respondents showed poor baseline knowledge of aflatoxin and its health risks. The campaign included monitoring of aflatoxin contamination in maize grains from market stores in 38 cities and towns. Aflatoxin concentration in contaminated samples ranged from 24 to 117.5 ng g-1 in Benin, from 0.4 to 490.6 ng g-1 in Ghana, and from 0.7 to 108.8 ng g-1 in Togo. The campaign significantly increased public awareness that populations were exposed to high levels of aflatoxin. The number of maize traders who were informed about the toxin increased 10.3 and 3.2 times in Togo and Benin, respectively; at least 33% more traders believed the information in each of Benin and Togo; 11.4 and 28.4% more consumers sorted out and discarded bad grains in Benin and Ghana, respectively. This paper concludes that sustained public education can help reduce aflatoxin contamination.  相似文献   

16.
A study to determine mould incidence and aflatoxin contamination of maize kernels was carried out among dealers (traders) in the three agroecological zones of Uganda. The maize kernels were categorized into those stored for two to six months or for more than six months to one year. Results indicate that the mean moisture content of the kernels was within the recommended safe storage levels of ≤ 15% but was significantly lower in the Highland maize kernels followed by the Mid-Altitude (dry) kernels while the Mid-Altitude (moist) kernels had the highest levels. Across the agroecological zones, Aspergillus, Fusarium, Penicillium and Rhizopus were the most predominant fungal genera identified and, among their species, A. niger had the highest incidence, followed by A. flavus, F. verticillioides, A. wentii, A. penicillioides and Rhizopus stolonifer. There were more aflatoxin positive samples from the Mid-Altitude (moist) zone (88%) followed by those samples from the Mid-Altitude (dry) zone (78%) while samples from the Highland zone (69%) were least contaminated. Aflatoxin levels increased with storage time such that maize samples from the Mid-Altitude (dry and moist) stored for more than six months had mean levels greater than the 20 ppb FDA/WHO regulatory limits. Aflatoxin B1 was the most predominant type and was found to contaminate maize kernels from all the three agroecological zones. These results indicate that maize consumers in Uganda are exposed to the danger of aflatoxin poisoning. Thus, there is the need for policy makers to establish and enforce maize quality standards and regulations related to moulds and aflatoxins across the agroecological zones to minimize health hazards related to consumption of contaminated kernels.  相似文献   

17.
Survey of aflatoxin contamination of dried figs grown in Turkey in 1986   总被引:2,自引:0,他引:2  
A total of 284 dried fig samples, collected from fields during drying, and from warehouse and processing units in the Aegean region of Turkey in 1986, were examined for aflatoxin contamination. Aflatoxin B1, B2, and G1 were detected in 4, 2, and 2% of the samples, respectively, which were of the lower grade of figs taken from the drying stage. The average alfatoxin levels in positive samples were estimated to be 112.3 (B1), 50.6 (B2), and 61.4 ng/g (G1). The samples collected from storage (64 samples) and processing units (14 samples) contained no aflatoxins. The results of this survey show that aflatoxin contamination of Turkish dried figs in 1986 was highly correlated with the poorer grade of fig.  相似文献   

18.
Mycotoxins are toxic, low molecular weight compounds produced by fungi. Among them, aflatoxins are the most carcinogenic and they mainly impact on rural communities of developing countries. The present study supplies data on mycobiota and aflatoxin contamination in the most common food products consumed in Haiti. The study concerns analyses performed on 49 samples of meals and seeds collected in South Haiti and tested for fungal occurrence and aflatoxin content by HPLC-DAD technique. The results revealed that three main fungal genera affected Haitian food products: Aspergillus spp. (Section Flavi and Nigri), followed by Penicillium spp. and Fusarium spp. Aflatoxin was present in more than half of the samples of maize (Zea mays L.) kernels (55%), maize meal (57%) and moringa (Moringa oleifera Lam.) seeds (64%), and in 25% of peanut (Arachis hypogaea L.) samples. The tested food products were mostly contaminated by aflatoxin B1 (AFB1) followed by aflatoxin B2 (AFB2), while no aflatoxins type G were detected. The total concentration of aflatoxins in the positive samples was 228 μg/kg on average, i.e., fifty-seven and eleven times higher than the maximum levels allowed in Europe and USA, respectively. Both the presence of aflatoxigenic fungi and aflatoxin contamination in maize kernels seemed to be related to agricultural practices, such as weed control, irrigation and growing cycle length. These findings suggest that the Haitian population is strongly exposed to aflatoxin risk. This risk could be reduced by exploiting simple and accessible farming strategies for minimizing mycotoxin contamination, at least for maize.  相似文献   

19.
Aflatoxin, produced by Aspergillus flavus, is one of the most toxic and carcinogenic substances known and contaminates many agricultural commodities such as corn, peanuts, cottonseed, and tree nuts. The challenge to breeders/plant pathologists is to identify lines that have resistance to aflatoxin production. Maize population GT-MAS:gk has been identified and released as a germplasm with resistance to aflatoxin contamination. In the present study, we assessed genetic divergence in the GT-MAS:gk population using restriction fragment length polymorphism (RFLP) DNA markers to survey 11 selfed inbred lines and conducted field evaluations for the dissimilarities in aflatoxin production among these inbred lines in comparison with a sister population, GT-MAS:pw.nf. The 11 selfed inbred lines were assayed for DNA polymorphism using 113 RFLP markers in 10 linkage groups covering 1,518.2 centimorgans (cM; unit of gene or chromosome size). Considerable variation among the inbreds was detected with RFLP markers, of which 42 probe-enzyme combinations gave 102 polymorphic bands. Cluster analysis based on genetic similarities revealed associations and variations among the tested lines. Three polymorphic groups were distinguished by cluster analysis. Two years of field evaluation data showed that aflatoxin concentrations among the lines were significantly different in both years (P < 0.001). Maturity data were also different. Thus, this study demonstrates that the maize population GT-MAS:gk is heterogeneous and that individuals may be different in resistance to A. flavus infection and aflatoxin production. Therefore, the most resistant lines should be inbred to increase homogeneity, and resistance should be confirmed through progeny testing.  相似文献   

20.
坚果和干果在生产、加工和储藏过程中易受到黄曲霉毒素污染。黄曲霉毒素是一类毒性极强的真菌毒素, 其中黄曲霉毒素B1污染最普遍、毒性最强, 其易引发急、慢性毒性, 致癌、致畸、免疫抑制等多种危害, 严重威胁果品安全, 危害人类健康。坚果和干果中黄曲霉毒素污染状况的阐释能够更加明晰其在不同果品中的污染差异, 为有针对性地控制毒素污染奠定了基础。坚果和干果中黄曲霉毒素的准确检测是分析其污染状况的前提。另外, 如何防控黄曲霉毒素在坚果和干果中的污染, 降低黄曲霉毒素对人类健康的影响, 一直是研究的重点。本文对国内外坚果和干果中黄曲霉毒素的污染情况及限量标准, 黄曲霉毒素的检测方法和防控措施进行了综述, 以期为坚果和干果中黄曲霉毒素的污染控制提供理论基础和指导。  相似文献   

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