Location: Peanut ResearchTitle: Mating-type heterokaryosis in Aspergillus flavus in North Carolina Author
Submitted to: Meeting Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 6/10/2012
Publication Date: 6/24/2012
Citation: Olarte, R.A., Horn, B.W., Worthington, C.J., Carbone, I. 2012. Mating-type heterokaryosis in Aspergillus flavus in North Carolina. MycoRed North America. June 24-28, 2012. Ottawa, Canada. Interpretive Summary: none required
Technical Abstract: Aspergillus flavus is a well-known pathogen of many important agricultural commodities and is a major producer of aflatoxins (AFs), which are carcinogenic polyketides that pose a serious health risk to humans and animals. Recently, heterokaryosis and the presence of cryptic alleles were shown to exist in A. flavus; cryptic AF cluster alleles were present in low copy number and were only detectable in ascospore isolates obtained from experimental crosses with at least one parent having a partial or completely missing AF gene cluster. In the present study, 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), and ninety single ascospore isolates were obtained 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. 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); 39% of isolates obtained from ascospores and 9% of isolates from soil after biocontrol treatments were heterokaryotic as well. The population genetic structure before and after the application of biocontrol treatments will be discussed. The vertical transmission of MAT1-1/MAT1-2 to progeny ascospore isolates suggests that heterokaryosis can be maintained in subsequent generations in natural populations. Moreover, serial transfer experiments in the laboratory indicate that conidial populations can be shifted to become heterokaryotic, and preliminary evidence suggests that heterokaryosis may be important in modulating toxicity. Further characterization of heterokaryons and their frequency in A. flavus populations will be important for understanding the adaptation of these fungi to changing environmental conditions.