Population structure of Aspergillus flavus before and after biocontrol treatment
R. A. OLARTE (1), B. W. Horn (2), C. J. Worthington (1), R. W. Heiniger (1), M. H. Lewis (1), P. S. Ojiambo (1), R. Singh (1), I. Carbone (1). (1) North Carolina State University, Raleigh, NC, U.S.A.; (2) National Peanut Research Laboratory, USDA ARS, Dawson, GA, U.S.A.
<i>Aspergillus flavus</i> is a fungal pathogen of many important crops worldwide. We sampled <i>A. flavus</i> strains from a cornfield in Rocky Mount, North Carolina, over a period of two years. Plots were inoculated at tasselling with either AF36 or NRRL 21882 (=Afla-Guard) biocontrol strains, both of which are mating type <i>MAT1-2</i>. Subsequently, toxigenic strain NRRL 3357 (<i>MAT1-1</i>) was applied to all plots. Sclerotia were collected from infected corn ears at harvest and ninety single-ascospore isolates were obtained from ascocarps. In addition, eighty <i>A. flavus</i> isolates were collected from soil one month after planting (before biocontrol application) and one and two years after biocontrol application. PCR revealed grouping of isolates into three distinct mating-type classes: <i>MAT1-1</i>, <i>MAT1-2</i> and <i>MAT1-1/MAT1-2</i>. A significant proportion (54%) of isolates sampled prior to biocontrol treatments and 39% of isolates obtained from ascospores were heterokaryotic for mating type (<i>MAT1-1/MAT1-2</i>). The population genetic structure before and after the application of biocontrol treatments will be discussed. The potential for the biocontrol strain to undergo sexual reproduction and the degree of relatedness of the biocontrol strain to the predominant indigenous lineage may influence the long-term success of a biocontrol strain. These findings will be instrumental in the selection of strains for use in next-generation biocontrol strategies.
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