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

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.大豆的分枝可塑性（branching plasticity），即其根据种植密度调整分枝发育的能力，因品种而异。需借助田间试验测定分枝可塑性程度，但此类试验耗时耗力，难以实现大量品种的分析与比较。因此亟需建立简便的评价方法，以对广泛的试验材料开展分枝可塑性研究。为此，本研究构建了两种估算该性状的方法。第一种方法：通过设置株距梯度（5、7.5、10、15、20、25、30 cm），探究分枝节数与行内种植距离的相关性。二者的回归直线斜率在大豆品种间存在显著差异，且与2015、2017年田间试验测定的分枝可塑性实测值呈显著相关。第二种方法：在V4期（大豆四叶期）于第一与第二叶节间摘除茎尖，待成熟后统计分枝节数。不同品种的分枝节数存在显著差异，且该数值与2015、2017年田间试验测定的分枝可塑性值呈显著正相关。综合田间管理与形态学调查所需的时间与人力成本，摘顶法被认为是评价分枝可塑性的高效且简便的方法。