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Sexual Reproduction in Aspergillus flavus Sclerotia Naturally Produced in Corn

January 2014 , Volume 104 , Number  1
Pages  75 - 85

Bruce W. Horn, Ronald B. Sorensen, Marshall C. Lamb, Victor S. Sobolev, Rodrigo A. Olarte, Carolyn J. Worthington, and Ignazio Carbone

First, second, third, and fourth authors: National Peanut Research Laboratory, United States Department of Agriculture–Agricultural Research Service, Dawson, GA; and fifth, sixth, and seventh authors: Center for Integrated Fungal Research, Department of Plant Pathology, North Carolina State University, Raleigh.

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Accepted for publication 12 July 2013.

Aspergillus flavus is the major producer of carcinogenic aflatoxins worldwide in crops. Populations of A. flavus are characterized by high genetic variation and the source of this variation is likely sexual reproduction. The fungus is heterothallic and laboratory crosses produce ascospore-bearing ascocarps embedded within sclerotia. However, the capacity for sexual reproduction in sclerotia naturally formed in crops has not been examined. Corn was grown for 3 years under different levels of drought stress at Shellman, GA, and sclerotia were recovered from 146 ears (0.6% of ears). Sclerotia of A. flavus L strain were dominant in 2010 and 2011 and sclerotia of A. flavus S strain were dominant in 2012. The incidence of S strain sclerotia in corn ears increased with decreasing water availability. Ascocarps were not detected in sclerotia at harvest but incubation of sclerotia on the surface of nonsterile soil in the laboratory resulted in the formation of viable ascospores in A. flavus L and S strains and in homothallic A. alliaceus. Ascospores were produced by section Flavi species in 6.1% of the 6,022 sclerotia (18 of 84 ears) in 2010, 0.1% of the 2,846 sclerotia (3 of 36 ears) in 2011, and 0.5% of the 3,106 sclerotia (5 of 26 ears) in 2012. For sexual reproduction to occur under field conditions, sclerotia may require an additional incubation period on soil following dispersal at crop harvest.

Additional keywords: Aspergillus parasiticus, biological control, Eupenicillium ochrosalmoneum.

This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 2014.