Plant architecture genes affect seed composition and seed weight in soybeans grown in the Midsouth USA

The Early Soybean Production System (ESPS) in the Midsouth is characterized by high humidity, high heat, water deficit, and disease pressure. Therefore, optimizing soybean plant architecture adapted to the ESPS is essential for maximizing seed yield (SY) and seed composition (nutrition). The objective of this research was to investigate the effect of plant architecture, i.e., stem termination genes on seed composition/nutrition (seed protein, oil, fatty acids, and sugars), and seed size (100-seed weight). We used a set of four near-isogenic stem termination lines from maturity group (MG) V that were adapted to the ESPS in the Midsouth. The four germplasm near-isogenic lines (NIL) are USDA-ARS-GDS-880 Dt1 (indeterminate), USDA-ARS-GDS-880dt1- t2 (tall determinate), and USDA-ARS-GDS-880 Dt2 (semi-determinate), and determinate- dt1 , with differing plant architectures derived from different stem termination genes. A 3-year field experiment was conducted in 2022, 2023, and 2024 at Stoneville. The results showed that the semi-determinate (semi-det), DS49-142, and Osage had higher seed protein content than the determinate (det), indeterminate (indet), and tall-determinate (tall-det) isolines in 2022, 2023, and 2024. Oil content in the semi-det was also higher than both checks, and comparable with the other genotypes. Oleic acid was higher in the semi-det and indet genotypes than in the det in 2022 and 2023. Raffinose content was higher in the tall-det and det isolines than in the semi-det isoline in 2022 and 2023, while stachyose was higher in the tall-det and indet isolines than in the semi-det type in 2023 and 2024. The 100-seed weight was highest in the semi-det, tall-det, and DS49–142 in all three years. Across the three years, and among the all lines, semi-det had the highest protein (38.95%), oleic acid (21.90%), and 100-seed weight (15.17 g). To our knowledge, this is the first report comparing these four plant architecture types in a MG V background in the ESPS in the Midsouth. This research demonstrated that the semi-det stem termination type contained the highest seed protein, acceptable levels of oil, and larger seed size than the other types. These are potentially desirable traits for soybean producers and the seed industry.