Interplay between quantitative trait loci for stem strength and agronomic traits in a wheat doubled-haploid population

Stem strength in wheat is important for mechanical stability, supporting nutrient translocation and lodging tolerance to uphold yield potential and grain quality. The main objectives of this study were to identify quantitative trait loci (QTLs) for stem strength and diameter and determine if stem biomechanical QTLs overlap with QTLs for yield and other agronomic traits. A doubled haploid wheat population between the distinct parents AC Cadillac and Carberry was assessed for stem biomechanical traits together with lodging, height, heading date, and yield parameters. Multi-environment QTL mapping was performed to identify potential QTL hotspots, facilitate ideotype analysis, and examine putative candidate genes. Phenotypic analyses across 6 field environments revealed significant variation for 16 stem and agronomic traits with only stem wall thickness, grain yield, and thousand-kernel-weight (TKW) not differing significantly between parents AC Cadillac and Carberry. The Reduced height ( Rht ) allele Rht-B1b , present in Carberry, was the main driver of trait differences within the population, not only reducing height but also traits such as stem bending moment and TKW. QTL mapping revealed loci for stem traits present on chromosomes 2B, 2D, 4B, 5A, 6A, 6B, 7A, and 7D. There were distinct overlaps of stem trait QTLs with those of other traits including a heading date QTL on 2B and as well as grain size QTLs on 2D, 6A, and 6B. QTLs on 2D, 6A, and 6B compensated for a decrease in TKW largely driven by Rht-B1b in Carberry and also promoted an overall increase in stem diameter and stem bending moment. The study revealed the complexity of optimizing for stem strength-related ideotypes given the possible interactions with agronomic traits such as grain size which may have contrasting priorities for allele selections. The most promising QTL hotspot on chromosome 6A drove increases in TKW, stem wall thickness and stem bending moment. The findings support broadening the scope of traits in stem biomechanical research studies to ensure pleiotropic effects, especially those on grain traits, are captured. The results obtained facilitate future work focused on the development of genetic markers for stem strength and overall germplasm improvement. • Multi-environment QTL mapping of stem and agronomic traits in Canadian spring wheat. • Interplay between grain size and stem strength traits and their overlapping QTL. • Balancing trait selections for optimal stem ideotype design in spring wheat breeding.