Submitted to: Molecular Ecology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/10/2009
Publication Date: 1/15/2010
Citation: Grubisha, L.C., Cotty, P.J. 2010. Genetic Isolation among Sympatric Vegetative Compatibility Groups of the aflatoxin-producing fungus Aspergillus flavus. Molecular Ecology. 19:269-280. Interpretive Summary: Aflatoxin, a carcinogenic fungal metabolite, contamination of crops is problematic worldwide. Contamination of important agricultural crops results in tremendous economic loss and human disease. Aspergillus flavus is a pathogen of animals and plants and is the primary cause of aflatoxin contaminatin of crops. Understanding relationships within A. flavus populations is important for understanding epidemiology of aflatoxin contamination and implementation of management plans. A. flavus populations in Arizona and Texas were analyzed with 24 microsatellite markers to assesslevels of genetic diversity and estimate migration rates. This is the first genetic study of sympatric populations of VCGs in A. flavus. The results from this work are important for implementation of plans for management of aflatoxin contamination of crops.
Technical Abstract: Aspergillus flavus, fungal pathogen of animals and both wild and economically important plants, is most recognized for producing aflatoxin, a cancer-causing secondary metabolite, that contaminates food and animal feed globally. A. flavus is asexual and has a vegetative incompatibility system that limits hyphal fusion and subsequent gene flow between individuals belonging to different vegetative compatibility groups (VCG). Attempts to reduce levels of aflatoxin contamination of agricultural crops include using indigenous VCGs that do not produce aflatoxin to competitively displace toxin-producing VCGs. Genetic isolation between VCGs is necessary for effective longterm management plans for reducing aflatoxin levels in agriculture. However, despite the economic and human health importance of aflatoxin, little is known about the population genetics of A. flavus. We found high levels of genetic differentiation between the three most common VCGs in sympatric populations in Arizona and Texas on cotton, based on 24 microsatellite markers and 221 clonecorrected samples. We found no evidence of recombination between VCGs, including between VCGs of opposite mating-type. This is the first study of any asexual Aspergillus species to find 1)high levels of genotypic diversity within VCGs, 2) evidence of recombination within VCGs, and 3)indirect evidence for an active parasexual cycle in natural populations. We conclude that the three VCG populations are distinct, very old, clonal lineages in which mutation, mitotic recombination and migration have provided mechanisms for genetic variability and adaptation.