Identification of QTLs Associated with Stem Breaking Strength and Development of InDel Markers in Soybean Using BSA-Seq

Stem lodging significantly reduces soybean yield stability, particularly under dense planting and intercropping systems. Stem breaking strength is a key component of lodging resistance, but its genetic basis remains incompletely understood. In this study, an F₂ population consisting of 167 individuals derived from a cross between nanxiadou25 (NXD25, high stem breaking strength) and Shiyuehuang (SYH, low stem breaking strength) was analyzed using bulked segregant analysis with whole-genome resequencing (BSA-Seq) to identify loci associated with stem breaking strength. The trait showed broad quantitative variation in the F₂ population, ranging from 20.1 to 673.7 N. Two extreme bulks were constructed using 30 plants with the highest values and 30 plants with the lowest values. QTL-seq detected 21 candidate intervals at the 95% confidence level, among which, three major loci on Chr07, Chr13, and Chr16 exceeded the 99% threshold and were designated qBR7.2, qBR13.1, and qBR16.1. By integrating large-effect SNP/InDel variation, marker development, RNA-seq profiling, and qRT-PCR validation, nine candidate genes were retained for further study, and three marker-linked genes were highlighted as high-priority candidates. RNA-seq identified 9617 differentially expressed genes between the two parents. In addition, three co-dominant InDel markers, Chr07_01, Chr13_17, and Chr16_83, showed phenotype-consistent polymorphism in extreme F₂ individuals. These findings provide valuable loci, candidate genes, and molecular markers for soybean lodging-resistance breeding.