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ARS Home » Research » Publications at this Location » Publication #321149
Title: Environmental distribution and genetic diversity of vegetative compatibility groups determine biocontrol strategies to mitigate aflatoxin contamination of maize by Aspergillus flavus

Author
item ATEHNKENG, JOSEPH - International Institute For Tropical Agriculture
item DONNER, MATTHIAS - University Of California
item OJIAMBO, PETER - North Carolina State University
item IKOTUN, BABATUNDE - International Institute For Tropical Agriculture
item AUGUSTO, JOAO - International Institute For Tropical Agriculture
item Cotty, Peter
item BANDYOPADHYAY, RANAJIT - International Institute Of Tropical Agriculture (IITA)

Submitted to: Microbial Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/21/2015
Publication Date: 1/9/2016
Citation: Atehnkeng, J., Donner, M., Ojiambo, P.S., Ikotun, B., Augusto, J., Cotty, P.J., Bandyopadhyay, R. 2016. Environmental distribution and genetic diversity of vegetative compatibility groups determine biocontrol strategies to mitigate aflatoxin contamination of maize by Aspergillus flavus. Microbial Biotechnology. 9(1):75-88.

Interpretive Summary: Aflatoxin is a carcinogenic fungal metabolite produced by members of Aspergillus section Flavi. Aspergillus flavus is a pathogen of animals and plants and is the primary cause of aflatoxin contamination of crops. Contamination results in tremendous economic loss and human disease and even death. The most effective way of reducing aflatoxin contamination of crops is through competitive exclusion of aflatoxin-producing VCGs with nonaflatoxin-producing (called atoxigenic) VCGs. Nigeria needs aflatoxin management tools. In order to select atoxigenic VCGs for use in Nigeria, the distributions of 25 VCGs were determined among 832 isolates from 52 locations distributed across the important maize and groundnut production areas. During co-inoculation with an aflatoxin-producer, atoxigenic isolates reduced aflatoxin contamination in grain by '96%. The work resulted in identification of widely distributed VCGs endemic to Nigeria, including AV0222, AV3279, AV3304, and AV16127. Members of these VCGs, are good candidates for active ingredients of atoxigenic strain based biocontrol products for the mitigation of aflatoxin contamination.

Technical Abstract: Maize infected by aflatoxin-producing Aspergillus flavus may become contaminated with aflatoxins and as a result, threaten human health, food security, and farmers’ income in developing countries where maize is a staple. Environmental distribution and genetic diversity of A. flavus can influence the effectiveness of atoxigenic isolates in mitigating aflatoxin contamination. However, such information has not been used to facilitate selection and deployment of atoxigenic isolates. A total of 35 isolates of A. flavus isolated from maize samples collected from three agroecological zones of Nigeria were used in this study. Ecophysiological characteristics, distribution, and genetic diversity of the isolates were determined to identify vegetative compatibility groups (VCGs). The generated data was used to inform selection and deployment of native atoxigenic isolates to mitigate aflatoxin contamination in maize. In co-inoculation with toxigenic isolates, atoxigenic isolates reduced aflatoxin contamination in grain by '96%. Twenty-five VCGs were inferred from the collected isolates based on complementation tests involving nitrate non-utilizing (nit-) mutants. To determine genetic diversity and distribution of VCGs across agroecological zones, 832 nit- mutants from fifty-two locations in eleven administrative districts were paired with one self-complementary nitrate auxotroph tester pair for each VCG. Atoxigenic VCGs accounted for 81.1% of the 153 positive complementations recorded. Genetic diversity of VCGs was highest in the Derived Savanna agroecological zone (H = 2.61) compared to the Southern Guinea Savanna (H = 1.90) and Northern Guinea Savanna (H = 0.94) zones. Genetic richness (H = 2.60) and evenness (E5 = 0.96) of VCGs were high across all agroecological zones. Ten VCGs (40%) had members restricted to the original location of isolation, while 15 VCGs (60%) had members located between the original source of isolation and a distance >400 km away. The present study identified widely distributed VCGs in Nigeria such as AV0222, AV3279, AV3304, and AV16127, whose atoxigenic members can be deployed for a region-wide biocontrol of toxigenic isolates to reduce aflatoxin contamination in maize.