Evaluating the Influence of Potassium Chloride on the Growth, Germination, and Interaction of <i>Sclerotinia sclerotiorum</i> and <i>Coniothyrium minitans</i>

Sclerotinia stem rot (SSR), caused by fungal pathogen <i>Sclerotinia sclerotiorum</i>, is one of the leading contributors to yield losses in soybean. The fungus forms sclerotia that persist through the off-season and germinate under favorable conditions to infect soybean. Among the practices used to manage SSR, biological control with <i>Coniothyrium minitans</i> is an effective strategy to suppress <i>S. sclerotiorum</i> through direct interaction. However, both <i>S. sclerotiorum</i> and <i>C. minitans</i>, can interact with soil amendments, including fertilizers, with implications for SSR management. Since potassium is widely applied in soybean production in Wisconsin, this study aimed to investigate the effect of KCl on <i>S. sclerotiorum</i>, <i>C. minitans</i>, and their interaction in vitro. While radial growth of <i>S. sclerotiorum</i> was unaffected by KCl concentration, linear models effectively described decrease in number of sclerotia produced and the increase in sclerotial diameter and weight with increasing KCl concentration. Oxalic acid production declined with increase in KCl concentration, which was best captured by a non-linear exponential model, while sclerotial germination time decreased according to a linear model. Radial growth of <i>C. minitans</i> exhibited a linear decline with increasing KCl concentration, whereas conidial germination remained unaffected. A non-linear logistic model revealed a positive effect of increasing KCl concentration on mycoparasitism of <i>C. minitans</i> on sclerotia of <i>S. sclerotiorum</i>. These findings provide insights into interactions of KCl with <i>S. sclerotiorum</i> and <i>C. minitans</i> that could inform the integration of potassium fertilization with biological control strategies for SSR management in the field.