Abstract
Twenty indeterminate soybean cultivars that were developed in Canada and the US, but had adapted to Hokkaido, were used to investigate seed yield and branching plasticity (i.e., ability to promote and suppress branching under low and high planting density conditions, respectively, thereby stabilizing yield across planting densities) in the central region of Hokkaido over 4 years: 2016, 2017, 2021, and 2024. Branching plasticity was evaluated using a simplified method based on the number of nodes at maturity in plants that were pinched at the second trifoliate leaf stage. Additionally, yield and yield components were examined under standard planting density conditions (16.7 plants m−2). Significant varietal differences were observed in branching plasticity, with relatively high branching plasticity values for later-maturing cultivars. Differences in branching plasticity were also observed among cultivars in the same maturity group. Moreover, significant negative correlations were detected between branching plasticity and annual stability (coefficient of variation across 4 years) of seed yield, number of nodes, pods per node, and total number of pods. These findings indicate that cultivars with high branching plasticity had stable yields, mostly because of their relatively stable number of nodes and pods, even in low-yielding years. Thus, screening for high branching plasticity using a simplified evaluation method is effective for identifying cultivars with a stable and high yield potential in indeterminate cultivars.
