Impacts of soybean breeding on shoot architecture

Abstract

Despite decades of steady soybean ( Glycine max (L.) Merr.) yield increases from improved cultivars, the accompanying changes in shoot architectural traits have been under‐researched. To address this, we analyzed 55 cultivars spanning eight decades of breeding and estimated a genetic gain for yield of 20.7 kg ha ⁻¹ year ⁻¹ in south‐central Minnesota‐adapted cultivars. Yield improvements were accompanied by significant architectural changes: Branch angle increased by 0.06° year ⁻¹ , while branching zone length and first branch height decreased. This indicates modern cultivars have broader andmore compact branches initiated closer to the ground. Leaflet length and width decreased, resulting in a 17% reduction in total leaflet area. Stem length was reduced by 26%, mainly due to shorter internodes in the middle and top stem portions. Modern cultivars showed a more compressed upper shoot architecture, contradicting our hypothesis that breeders indirectly selected for open canopies to increase light penetration. Crucially, these architectural modifications did not alter average canopy coverage or time to canopy closure. These findings will inform future efforts to modify shoot architecture, optimizing canopy structure for efficient light capture and higher soybean yield potential in soybean.