scholarly journals Variation in Occurrence and Aflatoxigenicity of Aspergillus flavus from Two Climatically Varied Regions in Kenya

Toxins ◽  
2020 ◽  
Vol 12 (1) ◽  
pp. 34 ◽  
Author(s):  
Ethel Monda ◽  
Joel Masanga ◽  
Amos Alakonya
Keyword(s):  
Biological Control ◽  
Aspergillus Flavus ◽  
Plant Pathogens ◽  
Cropping Systems ◽  
Bacterial Species ◽  
Climatic Conditions ◽  
Aflatoxin Contamination ◽  
Maize Cultivation ◽  
Bacillus Spp ◽  
Study Sites

Aflatoxins are carcinogenic chemical metabolites produced by Aspergillus spp. of the section Flavi. In Kenya, Aspergillus flavus is the most prevalent and has been associated with several acute and chronic aflatoxin outbreaks in the past. In this study, we evaluated the occurrence of A. flavus in soils from two agro-ecological regions with contrasting climatic conditions, aflatoxin contamination histories and cropping systems. Aspergillus spp. were first isolated from soils before the identification and determination of their aflatoxigenicity. Further, we determined the occurrence of Pseudomonas and Bacillus spp. in soils from the two regions. These bacterial species have long been associated with biological control of several plant pathogens including Aspergillus spp. Our results show that A. flavus occurred widely and produced comparatively higher total aflatoxin levels in all (100%) study sites from the eastern to the western regions of Kenya. For the western region, A. flavus was detected in 4 locations (66.7%) that were previously under maize cultivation with the isolates showing low aflatoxigenicity. A. flavus was not isolated from soils under sugarcane cultivation. Distribution of the two bacterial species varied across the regions but we detected a weak relationship between occurrence of bacterial species and A. flavus. We discuss these findings in the context of the influence of climate, microbial profiles, cropping systems and applicability in the deployment of biological control remedies against aflatoxin contamination.

Modelling the colonisation of maize by toxigenic and non-toxigenic Aspergillus flavus strains: implications for biological control

2008 ◽  
Vol 1 (3) ◽  
pp. 333-340 ◽  
Author(s):  
H. Abbas ◽  
R. Zablotowicz ◽  
H. Bruns
Keyword(s):  
Biological Control ◽  
Aspergillus Flavus ◽  
Growth Parameters ◽  
Biological Control Agent ◽  
Cyclopiazonic Acid ◽  
Aflatoxin Contamination ◽  
Tween 20 ◽  
Lag Phase ◽  
Gompertz Equation ◽  
Aflatoxin Accumulation

To successfully exploit biological control it is desirable to understand how the introduced agent colonises the host and interferes with establishment of the pest. This study assessed field colonisation of maize by Aspergillus flavus strains as biological control agents to reduce aflatoxin contamination. Maize (corn, Zea mays L.) ears were inoculated with A. flavus using a pin-bar technique in 2004 and 2005. Non-aflatoxigenic strains K49 (NRRL 30797) & CT3 (NRRL 30798) and toxigenic F3W4 (NRRL 30798) were compared against a carrier control (0.2% aqueous Tween 20). Ten ears were sampled over 12 to 20 days, visually assessed, and curves fit to a three compartment Gompertz equation or other best appropriate regressions. Aflatoxin was determined by HPLC and cyclopiazonic acid (CPA) by LC/MS. The Gompertz model describes growth parameters, e.g. growth constant, lag phase and maximum colonisation characterised patterns of maize colonisation for most inoculated treatments. Aflatoxin accumulation in maize inoculated with F3W4 was about 35,000 ng/g in 2004 and 2005, with kinetics of aflatoxin accumulation in 2005 well described by the Gompertz equation. Less than 200 ng/g was observed in maize inoculated with strains CT3 & K49 and accumulation was described by a linear or logistic model. Maize inoculated with strains CT3 and F3W4 accumulated a maximum of 220 and 169 µg/kg CPA, respectively, compared to 22 and 0.2 µg/kg in the control and K49 inoculated, respectively. This technique can be used to elucidate colonisation potential of non-toxigenic A. flavus in maize in relation to biological control of aflatoxin. The greatest reduction of aflatoxin and CPA in maize inoculated with strain K49 and Gompertz parameters on colonisation indicates its superiority to CT3 as a biological control agent. The dynamics of maize colonisation by A. flavus strains and subsequent mycotoxin accumulation generated by using the pin-bar technique has implications for characterising the competence of biocontrol strains for reducing aflatoxin contamination.

Identification of Aspergillus flavus Isolates as Potential Biocontrol Agents of Aflatoxin Contamination in Crops

2013 ◽  
Vol 76 (6) ◽  
pp. 1051-1055 ◽  
Author(s):  
L. J. ROSADA ◽  
J. R. SANT'ANNA ◽  
C. C. S. FRANCO ◽  
G. N. M. ESQUISSATO ◽  
P. A. S. R. SANTOS ◽  
...  
Keyword(s):  
Biological Control ◽  
Aspergillus Flavus ◽  
Filamentous Fungus ◽  
Microscopic Examination ◽  
Genetic Recombination ◽  
Aflatoxin Contamination ◽  
Biocontrol Agents ◽  
Biological Control Agents ◽  
Nit Mutants ◽  
The Stability

Aspergillus flavus, a haploid organism found worldwide in a variety of crops, including maize, cottonseed, almond, pistachio, and peanut, causes substantial and recurrent worldwide economic liabilities. This filamentous fungus produces aflatoxins (AFLs) B1 and B2, which are among the most carcinogenic compounds from nature, acutely hepatotoxic and immunosuppressive. Recent efforts to reduce AFL contamination in crops have focused on the use of nonaflatoxigenic A. flavus strains as biological control agents. Such agents are applied to soil to competitively exclude native AFL strains from crops and thereby reduce AFL contamination. Because the possibility of genetic recombination in A. flavus could influence the stability of biocontrol strains with the production of novel AFL phenotypes, this article assesses the diversity of vegetative compatibility reactions in isolates of A. flavus to identify heterokaryon self-incompatible (HSI) strains among nonaflatoxigenic isolates, which would be used as biological controls of AFL contamination in crops. Nitrate nonutilizing (nit) mutants were recovered from 25 A. flavus isolates, and based on vegetative complementation between nit mutants and on the microscopic examination of the number of hyphal fusions, five nonaflatoxigenic (6, 7, 9 to 11) and two nontoxigenic (8 and 12) isolates of A. flavus were phenotypically characterized as HSI. Because the number of hyphal fusions is reduced in HSI strains, impairing both heterokaryon formation and the genetic exchanges with aflatoxigenic strains, the HSI isolates characterized here, especially isolates 8 and 12, are potential agents for reducing AFL contamination in crops.

scholarly journals Monitoring Cropping Systems: From Data Collection to Cloud Database Storage Using Open Source Software

Proceedings ◽  
2020 ◽  
Vol 30 (1) ◽  
pp. 79
Author(s):  
Ioanna Panagea ◽  
Dangol Anuja ◽  
Marc Olijslagers ◽  
Jan Diels ◽  
Guido Wyseure
Keyword(s):  
Open Source ◽  
Open Source Software ◽  
Web Application ◽  
Cropping Systems ◽  
Cropping System ◽  
Query Languages ◽  
Climatic Conditions ◽  
Raw Data ◽  
Wide Range ◽  
Study Sites

Agricultural cropping systems and experiments include complex interactions of processes and various management practices and/or treatments under a wide range of environmental and climatic conditions. The use of standardized formats to monitor and document these systems and experiments can help researchers and stakeholders to efficiently exchange data, promote interdisciplinary collaborations, and simplify modelling and analysis procedures. In the scope of the SoilCare Horizon 2020 project monitoring and assessment work package, an integrated scheme to collect, validate, store, and access cropping system information and experimental data from 16 study sites, was created. The aim of the scheme is to make the data readily available in a way that the information is useful, easy to access and download, and safe, relying only on open source software. The database design considers data and metadata required to properly and easily monitor, process, and analyse cropping systems and/or agricultural experiments. The scheme allows for the storage of data and metadata regarding the experimental set-up, associated people and institutions, information about field management operations and experimental procedures which are clearly separated for making analysis procedures faster, links between system components, and information about the environmental and climatic conditions. Raw data are entered by the users into a structured spreadsheet. The quality is checked before storing the data into the database. Providing raw data allows processing and analysing as each other user needs. A desktop import application has been created to upload the information from spreadsheet to database, which includes automated error checks of relationship tables, data types, data constraints, etc. The final component of the scheme is the database web application interface, which enables users to access and query the database across the study sites without the knowledge of query languages and to download the required data. For this system design, PostgreSQL is used for storing the data, pgAdmin 4 for database management administration, MongoDB for user management and authentication, Python for the development of the import application, Angular and Node.js/Express for the web application and spreadsheets compatible with LibreOffice Calc. The system is currently tested with data provided by the SoilCare study sites. Preliminary testing indicated that extended quality control of the spreadsheets was required from the system’s administrator to meet the standards and restrictions of the import application. Initial comments from the users indicate that the database scheme, even if it initially seems complicated, includes all the variables and details required for a complete monitoring and modelling of an agricultural cropping system.

Atoxigenic Aspergillus flavus biological control of aflatoxin contamination: what is the mechanism?

2015 ◽  
Vol 8 (2) ◽  
pp. 235-244 ◽  
Author(s):  
K.E. Damann Jr.
Keyword(s):  
Biological Control ◽  
Aspergillus Flavus ◽  
Population Biology ◽  
Aflatoxin Production ◽  
Infection Process ◽  
Aflatoxin Contamination ◽  
Signal Molecules ◽  
Nutrient Competition ◽  
Toxigenic Strain ◽  
Aflatoxin Inhibition

The term ‘competitive exclusion’ involving physical blockage of growth or access of the toxigenic strain to the seed target has been used to describe the mechanism of biological control of aflatoxin contamination. However, recent evidence suggests that a form of intraspecific aflatoxin inhibition requiring growth of the competing strains together during the infection process in such a way that hyphae physically interact or touch is the trigger for preventing induction of aflatoxin synthesis. This direct touch-based inhibition of aflatoxin synthesis is posited to be the mechanistic basis of biological control in this system. Evidence for this idea comes from the published observations that co-culture of toxigenic and atoxigenic strains in a suspended disc system, in which the hyphae physically interact, prevents aflatoxin production. However, growth of the same strains in the same medium in the two compartments of a filter insert plate well system, separating the atoxigenic and toxigenic strains with a 0.4 μm or 3.0 μm filter, allows aflatoxin production approaching that of the toxigenic strain alone. When the strains are mixed and placed in both the insert and the well compartments, the intraspecific aflatoxin inhibition occurs as it did in the suspended disc culture system. This further suggests that neither nutrient competition nor soluble signal molecules, which should pass through the filter, are involved in intraspecific aflatoxin inhibition. When the two strains are separated by a 12 μm filter that would allow some passage of conidia or hyphae between the compartments the aflatoxin synthesis is approximately half that of the toxigenic strain alone. This phenomenon could be termed ‘competitive inclusion’ or ‘competitive phenotype conversion’. Work of others that relates to understanding the phenomenon is discussed, as well as an Aspergillus flavus population biology study from the Louisiana maize agro-ecosystem which has biological control implications.

Aflatoxin Reduction in Corn Through Field Application of Competitive Fungi†

1999 ◽  
Vol 62 (6) ◽  
pp. 650-656 ◽  
Author(s):  
JOE W. DORNER ◽  
RICHARD J. COLE ◽  
DONALD T. WICKLOW
Keyword(s):  
Biological Control ◽  
Aspergillus Flavus ◽  
Weather Conditions ◽  
Type A ◽  
Field Application ◽  
Aflatoxin Contamination ◽  
Applied Strain ◽  
Wild Type ◽  
Separate Part ◽  
Aflatoxin Concentration

Soil in corn plots was inoculated with nonaflatoxigenic strains of Aspergillus flavus and A. parasiticus during crop years 1994 to 1997 to determine the effect of application of the nontoxigenic strains on preharvest aflatoxin contamination of corn. Corn plots in a separate part of the field were not inoculated and served as controls. Inoculation resulted in significant increases in the total A. flavus/parasiticus soil population in treated plots, and that population was dominated by the applied strain of A. parasiticus (NRRL 21369). In the years when weather conditions favored aflatoxin contamination (1996 and 1997), corn was predominately colonized by A. flavus as opposed to A. parasiticus. In 1996, colonization by wild-type A. flavus was significantly reduced in treated plots compared with control plots, but total A. flavus/parasiticus colonization was not different between the two groups. A change to a more aggressive strain of A. flavus (NRRL 21882) as part of the biocontrol inoculum in 1997 resulted in a significantly (P < 0.001) higher colonization of corn by the applied strain. Weather conditions did not favor aflatoxin contamination in 1994 and 1995. In 1996, the aflatoxin concentration in corn from treated plots averaged 24.0 ppb, a reduction of 87% compared with the aflatoxin in control plots that averaged 188.4 ppb. In 1997, aflatoxin was reduced by 66% in treated corn (29.8 ppb) compared with control corn (87.5 ppb). Together, the data indicated that although the applied strain of A. parasiticus dominated in the soil, the nonaflatoxigenic strains of A. flavus were more responsible for the observed reductions in aflatoxin contamination. Inclusion of a nonaflatoxigenic strain of A. parasiticus in a biological control formulation for aflatoxin contamination may not be as important for airborne crops, such as corn, as for soilborne crops, such as peanuts.

Reduction in Aflatoxin Content of Maize by Atoxigenic Strains of Aspergillus flavus

1991 ◽  
Vol 54 (8) ◽  
pp. 623-626 ◽  
Author(s):  
ROBERT L. BROWN ◽  
PETER J. COTTY ◽  
THOMAS E. CLEVELAND
Keyword(s):  
Biological Control ◽  
Aspergillus Flavus ◽  
Aflatoxin Contamination ◽  
Biological Control Agents ◽  
Field Plot ◽  
Toxigenic Strain ◽  
Aflatoxin Content ◽  
Potential Use

In field plot experiments, an atoxigenic strain of Aspergillus flavus interfered with preharvest aflatoxin contamination of corn when applied either simultaneously with or one day prior to a toxigenic strain. The atoxigenic strain reduced preharvest aflatoxin contamination 80 to 95%. The atoxigenic strain was also effective in reducing postharvest aflatoxin contamination caused by both an introduced toxigenic strain and by strains resident on the kernels. The results suggest that atoxigenic strains of A. flavus may have potential use as biological control agents directed at reducing both preharvest and postharvest aflatoxin contamination of corn.

Mitigation of Aflatoxin Contamination in Groundnuts using Trichoderma viride

2021 ◽  
Vol 25 (12) ◽  
pp. 32-43
Author(s):  
D. Syamala ◽  
S. Nabanita Kumar ◽  
P. Lalitha
Keyword(s):  
Biological Control ◽  
Aspergillus Flavus ◽  
Trichoderma Viride ◽  
Culture Technique ◽  
Aflatoxin Contamination ◽  
Dual Culture ◽  
Chemical Methods ◽  
Post Harvest ◽  
Carcinogenic Agents ◽  
Physical And Chemical

Groundnuts are often prone to contamination by Microorganisms during pre-harvest or post-harvest storage. One such contaminant is Aspergillus flavus which is abundantly found in soil and air. Several strains of A. flavus are known to produce mycotoxins named as aflatoxins. These aflatoxins are potent carcinogenic agents whose destruction has become a challenging task in the present scenario. Various physical and chemical methods are available to eliminate the growth of Aspergillus flavus but these methods have several demerits. The present study is based on biological control of Aspergillus flavus using Trichoderma viride strain TV 10. Antagonistic studies of Tv 10 against A.flavus were carried out by performing dual culture technique.

scholarly journals Identification of Atoxigenic Aspergillus flavus Isolates to Reduce Aflatoxin Contamination of Maize in Kenya

Plant Disease ◽  
2011 ◽  
Vol 95 (2) ◽  
pp. 212-218 ◽  
Author(s):  
C. Probst ◽  
R. Bandyopadhyay ◽  
L. E. Price ◽  
P. J. Cotty
Keyword(s):  
Biological Control ◽  
Aspergillus Flavus ◽  
Aflatoxin Contamination ◽  
Fungal Communities ◽  
Management Tools ◽  
Maize Production ◽  
Vegetative Compatibility Groups ◽  
Potential Value ◽  
Maize Sample ◽  
Maize Kernels

Aspergillus flavus has two morphotypes, the S strain and the L strain, that differ in aflatoxin-producing ability and other characteristics. Fungal communities on maize dominated by the S strain of A. flavus have repeatedly been associated with acute aflatoxin poisonings in Kenya, where management tools to reduce aflatoxin levels in maize are needed urgently. A. flavus isolates (n = 290) originating from maize produced in Kenya and belonging to the L strain morphotype were tested for aflatoxin-producing potential. A total of 96 atoxigenic isolates was identified from four provinces sampled. The 96 atoxigenic isolates were placed into 53 vegetative compatibility groups (VCGs) through complementation of nitrate non-utilizing mutants. Isolates from each of 11 VCGs were obtained from more than one maize sample, isolates from 10 of the VCGs were detected in multiple districts, and isolates of four VCGs were found in multiple provinces. Atoxigenic isolates were tested for potential to reduce aflatoxin concentrations in viable maize kernels that were co-inoculated with highly toxigenic S strain isolates. The 12 most effective isolates reduced aflatoxin levels by >80%. Reductions in aflatoxin levels caused by the most effective Kenyan isolates were comparable with those achieved with a United States isolate (NRRL-21882) used commercially for aflatoxin management. This study identified atoxigenic isolates of A. flavus with potential value for biological control within highly toxic Aspergillus communities associated with maize production in Kenya. These atoxigenic isolates have potential value in mitigating aflatoxin outbreaks in Kenya, and should be evaluated under field conditions.

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