P-269 - Identification of genetic specificities deriving organic acid responsiveness influencing soybean-Sclerotinia sclerotiorum interactions

White mold caused by Sclerotinia sclerotiorum (Ss) is a devastating disease that affects soybean production worldwide. Recently, there has been an increasing trend toward incorporating organic fertilizers, which produce organic acids (OAs) upon decomposition. These OAs have been shown to positively impact plant and soil health while also suppressing various pathogens. In this study, we are investigating how OAs in soil can influence the soybean-white mold pathosystem. Extensive field surveys conducted in 2023 and 2024 in South Dakota's soybean-growing regions led to the collecting of 107 Ss isolates. These isolates were screened for organic acid responsiveness, using chemical humic acid and fulvic acid (FA) as proxies and applying a concentration gradient ranging from 20 to 150 mg/L. Our results identified both positive and negative correlations (p< 0.05, ANOVA) for sclerotia size, mycelial growth, and sclerotia number, reflecting potential genetic variation that leads to differential responses. We have selected two isolates with contrasting FA responses for in-planta assays on soybean lines Williams 82 and PI 416805, while concurrently performing whole genome sequencing and transcriptomics of 25 isolates on the Oxford Nanopore long-read sequencing platform to identify pathogen-specific genomic variabilities that modulate the soybean-white mold interactions in the presence of OAs. This farm-oriented functional genomics research will provide critical insights into the OA-responsive pathways that shape soybean-white mold interactions for enhancing soybean resistance.