ABSTRACT To elucidate the effects of maturity and the stem growth habit on the planting density-dependent branching plasticity of soybean cultivars, we studied the branch traits of 12 cultivars or lines planted at different densities (8.3, 16.7, and 22.2 plants m−2) in Sapporo (2012) and Ebetsu (2013). The 12 cultivars and lines consisted of three determinate cultivars from Hokkaido, three indeterminate cultivars from the northern US, and near-isogenic lines with the backgrounds of Canadian, US, and Japanese cultivars exhibiting diverse stem growth habits. We investigated the relationship between the maturity or stem growth habit and branching plasticity, which was calculated based on the ratios of different branch traits under sparse and dense planting conditions. The use of the ratios of the total branch length and the number of nodes per branch under sparse and dense planting conditions as a measure of branching plasticity revealed varietal differences across years. For the determinate and indeterminate cultivars in both years, branching plasticity was positively correlated with the number of days until stage R5 (onset of seed filling), which is when branches cease to elongate. Comparisons of Japanese and US cultivars and near-isogenic lines for the Dt1 gene (mediating the stem growth habit) indicated that the branching plasticity of indeterminate cultivars and lines is greater than that of determinate cultivars, with a large variation among backgrounds and cultivars. The results of this study imply that branching plasticity is greater in late-maturing soybean cultivars. Moreover, the indeterminate growth habit substantially enhances branching plasticity. GRAPHICAL ABSTRACT

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成熟组和茎生长习性对不同种植密度大豆品种分枝可塑性的影响

摘要 为了阐明成熟度和茎生长习性对大豆品种种植密度依赖性分枝可塑性的影响，我们研究了以不同密度种植的 12 个品种或品系的分枝性状（8.3、16.7 和 22.2 株 m-2）在札幌（2012）和江别（2013）。这12个品种和品系包括来自北海道的三个确定品种、三个来自美国北部的不确定品种，以及以加拿大、美国和日本品种为背景的近等基因系，表现出不同的茎生长习性。我们研究了成熟度或茎生长习性与分枝可塑性之间的关系，分枝可塑性是根据疏密和密植条件下不同分枝性状的比率计算得出的。在稀疏和密集种植条件下，使用总分枝长度和每个分枝节点数的比率作为分枝可塑性的衡量标准，揭示了不同年份的品种差异。对于这两年的确定和不确定品种，分枝可塑性与R5阶段（种子灌浆开始）前的天数呈正相关，此时分枝停止伸长。日本和美国品种和近等基因系的Dt1基因（介导茎生长习性）的比较表明，不确定品种和品系的分枝可塑性大于确定品种，背景和品种之间差异较大。这项研究的结果意味着晚熟大豆品种的分枝可塑性更大。而且，不确定的生长习性大大增强了分枝可塑性。图形概要