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Effect of temperature and biological control agents on mycelial growth and sclerotia development of Sclerotinia sclerotiorum and Sclerotium rolfsii

Zelalem Mersha: Virginia State University

<div><em>Sclerotinia sclerotiorum</em> (<em>Ss</em>) and <em>Sclerotium rolfsii</em> (<em>Sr</em>) are soilborne pathogens affecting many vegetables in Missouri. <em>Ss</em> causes a number of diseases including white mold, timber rot and lettuce drop. If unmanaged and when conditions are favorable, these diseases could result in a significant yield loss. <em>Sr</em> causes southern blight on tomatoes and incidence of the disease has increased recently. Options to control these pathogens are limited due to wide host range, lack of resistant varieties, and sclerotia which can survive long time in the soil. Knowledge of the conducive environment for these pathogens is crucial to growers from the disease management perspective. In 2014 and 2015, <em>in vitro</em> experiments were carried out using a potato dextrose agar (PDA) medium. A single sclerotium was aseptically placed at the center and incubated at different temperatures (4, 17, 20, 25, 30, 35 and 40 °C). Radial growth of mycelial colony was measured at 2-day intervals and the time of sclerotia formation was recorded. Mycelial growth was faster and days to sclerotium formation of Ss were shorter at 17, 20 and 25°C compared to temperatures > 30°C, which halted development. <em>Coniothyrium minitans</em> and <em>Trichoderma spp.</em> significantly reduced the number of sclerotia produced by <em>Ss</em>. At 4°C, <em>Ss</em> grew significantly slow but none of the <em>Sr</em> grows at this temperature. For <em>Sr</em>, mycelial growth was faster and days to sclerotium formation were shorter at 25 and 30°C than 17 and 20°C. <em>Sr</em> mycelia grew at 35°C but no sclerotia were formed.</div>