Submitted to: Mycological Society of America
Publication Type: Abstract Only
Publication Acceptance Date: 4/10/2012
Publication Date: 4/24/2012
Citation: Olarte, R.A., Horn, B.W., Worthington, C.J., Carbone, I. 2012. Mating-type heterokaryosis and population shifts in Aspergillus flavus. Mycological Society of America. Interpretive Summary: None required.
Technical Abstract: Aspergillus flavus is a fungal pathogen of many agronomically important crops worldwide. We sampled A. flavus strains from a cornfield in Rocky Mount, NC. This field was planted in 2010 and plots were inoculated at tasselling with either AF36 or NRRL 21882 (=Afla-Guard) biocontrol strains, both of which are mating type MAT1-2. Subsequently, toxigenic strain NRRL 3357 (MAT1-1) was applied to all plots, including control plots not inoculated with biocontrol strains. Sclerotia were harvested from infected corn ears approximately 4.5 months after planting (2.5 months after biocontrol treatment); ninety single-ascospore isolates were isolated from ascocarps originating from plots treated with AF36 and NRRL 21882. In addition, eighty A. flavus isolates were collected from soil one month after planting (before biocontrol application) and one year after biocontrol application, for a grand-total of 250 isolates. Aflatoxin (AF) and cyclopiazonic acid (CPA) production were determined using standard thin-layer chromatography and HPLC. Three distinct toxin classes were identified: AF-/CPA-, AF+/CPA+ and AF-/CPA+. PCR amplification revealed grouping of isolates into three distinct mating-type classes: MAT1-1, MAT1-2 and MAT1-1/MAT1-2. A significant proportion (54%) of isolates sampled prior to biocontrol treatments were heterokaryotic for mating type (MAT1-1/MAT1-2), and 39% of isolates obtained from ascospores were heterokaryotic as well as 9% of isolates from soil after biocontrol treatments. The vertical transmission of MAT1-1/MAT1-2 to progeny ascospore isolates suggests that heterokaryosis can be maintained in subsequent generations. The genetic structure of the indigenous population before and after the application of biocontrol treatments will be discussed. Further characterization of heterokaryons and their frequency in A. flavus populations may be important in understanding the adaptation of these fungi to changing environmental conditions.