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The biology and etiology of Syzygites megalocarpus, an emerging pathogen of the button mushroom Agaricus bisporus

John de Soto: Pennsylvania State University

<div><em>Syzygites megalocarpus</em> is a fungal (Mucoromycotan) pathogen that infects other fungi, including <em>Agaricus bisporus</em>, the button mushroom. The pathogen recently appeared on a commercial Pennsylvania mushroom farm and has since become a reoccurring problem on many farms. The first objective was to test the effectiveness of two fungicides on <em>S. megalocarpus </em>by measuring mycelial growth rates on plates amended with the fungicides. Neither of the 2 fungicides killed the pathogen or had a great effect on growth rate. The second objective was to establish sporangiospores’ thermal death point to determine if current commercial composting parameters would kill the pathogen. Results indicated that <em>S. megaloacarpus</em> sporangiospores have a low thermal death point and did not survive exposure to temperatures above 37 ºC for 30 minutes, indicating that mushroom composting parameters are more than adequate to kill the pathogen. These results imply that infection in cropping systems must be due to secondary contamination of the compost after pasteurization. The third objective was to determine the susceptibility of several, widely used commercial mushroom strains to <em>S. megalocarpus</em> infection. Three brown and one white strains were inoculated with both plugs and spore suspensions of <em>S</em>.<em> megalocarpus </em>to determine susceptibility levels of different strains as well as to determine if a spore suspension or mycelial plug better initiates disease symptoms. These experiments are still ongoing.</div>