Simplified estimation of branching plasticity of soybean cultivars in relation to planting density by branch development in the row with the gradient of distance between plants and after pinching

Abstract

The branching plasticity of soybean, i.e. its ability to adjust branch development to planting density, differs among cultivars. Field experiments are required to measure the degree of branching plasticity, but such experiments require a great deal of time and labor, and it is difficult to analyze and compare a large number of cultivars. A simple evaluation method needs to be established to investigate branching plasticity for a wide range of materials. Therefore, we conducted two methods to estimate this value. In the first method, we investigated the relationship between the number of branching nodes and intra-row planting distance with a gradient of distance between plants (5, 7.5, 10, 15, 20, 25, and 30 cm). The slope of the regression line between these two factors revealed significant differences among soybean cultivars, and was correlated with the measured values of branching plasticity determined in field experiments in 2015 and 2017. In the second method, the top of the stem was pinched out between the first and second leaf nodes at the V4 stage, and then the number of branch nodes was counted at maturity. There were differences in the number of branching nodes among cultivars, and a significant positive correlation between these values and the branching plasticity values measured in the 2015 and 2017 field experiments. Considering the time and effort required for field management and morphological surveys, the pinching method is considered to be an effective and simple method to evaluate branching plasticity.