Novel QTL for Stem Strength Across Basal Internodes Enhance Understanding of Wheat Lodging Resistance

Stem lodging critically limits wheat yield stability, with its resistance heavily influenced by internode mechanical strength, a trait whose genetic architecture remains poorly resolved. This study aimed to dissect the genetic basis of stem strength in the first three basal internodes of wheat. Using a panel of 224 cultivars, we measured internode strength across two environments and performed a genome-wide association study with 269,708 SNPs, employing the FarmCPU model. Three stable quantitative trait loci (QTL) associated with internode stem strength were identified: QI1SS.sau.5A, QI2SS.sau.2D, and QI2SS.sau.6B across a diverse wheat panel, with allele-dependent effects observed among accessions. Among them, QI2SS.sau.2D consistently enhanced stem strength across all three internodes, explaining up to 10.8% of phenotypic variance, without adverse effects on plant height or thousand-grain weight. In contrast, the other two QTL were associated with trade-offs, such as reduced plant height or grain weight. These results reveal a polygenic and partially internode-shared genetic regulation of stem strength. The locus QI2SS.sau.2D is highlighted as a particularly promising, penalty-free target for marker-assisted selection to improve lodging resistance while maintaining agronomic performance, including plant height and thousand-grain weight.