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Sporulation and dispersal of the biological control agent Aspergillus flavus AF36 under field conditions in nut crops in California

Ramon Jaime: University of California, Davis/Kearney Agricultural Research and Extension Center

<div>Aflatoxins, produced by <em>Aspergillus </em>section<em> Flavi</em>, are potent natural carcinogens and widely regulated in foods and feeds. California nut crops are occasionally contaminated with aflatoxins. The biocontrol based on atoxigenic strains of <em>A. flavus</em> is a proven method to reduce aflatoxin contamination in crops and is approved for use in nut crops in California. However, a significant portion of treatments may not be fully successful due to poor sporulation or loss of the product. To optimize biocontrol treatments in nut crops, information about the epidemiology of the atoxigenic strain is essential. The objectives of present studies were to describe the behavior of the biocontrol agent and determine optimal conditions for sporulation and dispersal in orchards. The dispersal of the fungus across vertical and lateral dimensions from the source was studied and results indicate that the fungus successfully spreads upwards and laterally, but the rate of dispersal was exponentially inverse to both height and distance. Rapid sporulation of the product is required to avoid product loss and for optimal dispersal. Our results also indicate that the product has optimal sporulation at a soil water content between 13 and 18%. Product under suboptimal conditions had delayed sporulation and was exposed to arthropod predation (<em>Oniscidea</em> spp. and ants), while on soils with excess water content it decayed. This information is useful to optimize biocontrol treatments in nut crops.</div>