LAUSR

Pythium spp. is one of the major groups of pathogens that cause seedling diseases on soybean, leading to both pre- and post-emergence damping-off and root rot. More than 100 species have been identified within this genus, with P. irregulare, P. sylvaticum, P. ultimum var ultimum, and P. torulosum, being particularly important for soybean production given their aggressiveness, prevalence, and abundance in production fields. This study investigated the antagonistic activity of potential BCAs native to the US Midwest against Pythium spp. First, in vitro screening identified BCAs that inhibit P. ultimum var. ultimum growth. Scanning electron microscopy demonstrated evidence of mycoparasitism of all potential biocontrol isolates against the Pythium ultimum var. ultimum and P. torulosum, with the formation of appressorium-like structures, short-hyphal branches around host hyphae, hook-shaped structures, coiling, and parallel growth of the mycoparasite along the host hyphae. Based on these promising results, selected BCAs were tested under field conditions against six different Pythium spp. Trichoderma afroharzianum 26 used alone and a mix of Trichoderma hamatum 16 + T. afroharzianum 19 used as seed treatments protected soybean seedlings from Pythium spp. infection, as BCA-treated plots had on average 15-20% increase on plant stand and increased vigor compared with control plots. Our results also indicate that some of these potential biocontrol agents could be added with a fungicide seed treatment with minimum inhibition occurring, depending on the fungicide active ingredient. This research highlights the need for the development of tools to incorporate biological control as a facet of soybean seedling disease management programs. The harnessing of native biological control agents (BCA) is a potential tool that could be integrated with other management strategies to provide efficient control of seedling diseases.