Email: Simeon.ntawugurana@mail.huji.ac.il

Water deficit is the primary environmental constraint affecting wheat growth and production and is increasingly exacerbated due to climate change. Previously, we showed that crop investment in stem structural biomass and stem water-soluble carbohydrates promote grain filling and yield under water-stress conditions. Thus, underpinning the genetic architecture of stem traits under water stress could serve as a basis for future breeding of climate-resilience wheat.

Here, we evaluated the bread wheat diversity panel WheatMore (n=300) under contrasting water availabilities: Well-watered (~700mm) and water-limited (~350mm) in a rainout shelter facility in Rehovot, Israel. The focus was given to stem morphology traits: Internode diameter, stem solidness, peduncle length, and yield-related traits: Above-ground biomass, thousand-grain weight, and grain yield. Under water-limited conditions, structural stem biomass was reduced, as expressed in shorter peduncle lengths and narrow diameters.

Consequently, grain size and yield were reduced by 12.5% and 21.7%, respectively. Under both water availabilities, increased investment in stem internode diameter and peduncle length were positively associated with grain size. The panel was genotyped using 90K arrays, resulting in 26, 435 SNPs. A genome-wide association study (GWAS) was applied to detect genomic regions associated with stem traits. We identified a total of 81 highly significant markers for stem traits, with majority of 62 identified across environments (consecutive), 11 and 8 were detected only under well-watered and water-limited conditions, respectively (adaptive).

Major consecutive quantitative trait loci (QTL), both previously reported, were identified for stem solidness on chromosomes 3B and 3D, explaining 40.82% and 38.53% of the phenotypic variance under the two treatments. Adaptive QTLs were identified for internode diameter on chromosome 1D (14.74%) under well-watered and 3A (5%) under water-limited.

For peduncle length, adaptive QTLs were identified on chromosome 2B (with 4.1%) under WW and 6A (5.3% PVE) under WL environment. Out of these adaptive QTLs, only the one on 3A was previously reported.

Our results suggest that selecting spring wheat genotypes with wider internode diameter and long peduncle could be a valuable strategy to improve grain size under water stress conditions without compromising yield potential. These findings open new avenues for further research on the genetic basis underlying stem traits and for marker-assisted breeding of climate-resilient wheat.