Identification of a Quantitative Trait Locus on Chromosome 15 Conferring Resistance to <i>Pythium irregulare</i> in Soybean

Pythium irregulare (syn. Globisporangium irregulare) has emerged as a key contributor to soybean yield losses, showing consistently high prevalence and aggressiveness across multiple geographic surveys for soybean seedling disease. High levels of cross-pathogenicity limit crop rotation management strategies. This, coupled with increasing reports of fungicide insensitivity, underscores the urgent need to investigate and develop genetic resistance in soybean. In an earlier germplasm screening and genome-wide association study, we identified a soybean accession, PI 548360, that displayed stable levels of resistance when challenged with two distinct isolates of P. irregulare. In the current study, we developed an F 2:3 mapping population through a biparental cross between PI 548360 (partially resistant) and PI 548631 (highly susceptible to P. irregulare) and identified a 1.18-Mbp quantitative trait locus (QTL) interval on chromosome 15 responsible for 11.64% of the variation in post-emergent disease visual severity. This QTL region contains 80 predicted genes, several of which are associated with pathogen recognition, defense signaling, and necrotrophic pathogen resistance mechanisms. The molecular markers linked to this QTL are reported here and can help facilitate marker-assisted selection and genomic prediction for breeding soybeans with improved resistance to P. irregulare. [Formula: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 “No Rights Reserved” license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law, 2025.