Soybean (Glycine max (L.) Merr.) meets a large portion of its nitrogen (N) need via biological N2 fixation, which is highly sensitive to drought stress. Nitrogen isotope ratios between 15N and 14N (δ15N) can be used as a metric for relative differences among soybean genotypes for N2 fixation, as δ15N is negatively associated with N2 fixation. This study aimed to dissect the genetic basis of δ15N using a mapping population of 196 F6-derived recombinant inbred lines developed from a cross between PI 416997 and PI 567201D that was evaluated in multiple environments. There was a wide range of δ15N in all environments and narrow-sense heritability for δ15N was 35% when estimated across environments. Analysis of variance of δ15N showed significant effects of genotype and environment, whereas the genotype × environment interaction was not significant (P < 0.05). Inclusive composite interval mapping for individual environments identified 10 additive QTLs on seven chromosomes with additive effects ranging from 0.02 to 0.13‰ and that individually explained phenotypic variations from 1.72 to 9.34%. In total, eight QTL × environment interactions were found, and several genomic regions were involved in QTL × QTL interactions that were not identified as additive QTLs. These identified QTLs were co-localized with genomic regions associated with N2 fixation and other physiological traits identified in previous studies. A search for candidate genes resulted in detection of genes for nodulation and N-metabolism underlying many additive and epistatic QTLs. These identified regions may serve as potential targets for enhancing N2 fixation in soybean.

中文翻译：

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大豆中植物氮同位素比（δ15N）的数量性状位点（QTL）定位

大豆（Glycine max (L.) Merr.）通过对干旱胁迫高度敏感的生物固氮来满足大部分氮 (N) 需求。15N 和 14N 之间的氮同位素比率 (δ15N) 可用作衡量大豆基因型之间在 N2 固定方面的相对差异的指标，因为 δ15N 与 N2 固定呈负相关。本研究旨在使用由 PI 416997 和 PI 567201D 之间的杂交开发的 196 个 F6 衍生重组自交系的作图群体来剖析 δ15N 的遗传基础，并在多种环境中进行评估。所有环境中的 δ15N 范围很广，在跨环境估计时，δ15N 的狭义遗传率为 35%。δ15N 的方差分析表明受基因型和环境的显着影响，而基因型×环境相互作用不显着（P < 0.05）。单个环境的包容性复合区间映射在 7 条染色体上确定了 10 个加性 QTL，加性效应范围从 0.02 到 0.13‰，单独解释了 1.72 到 9.34% 的表型变异。总共发现了 8 个 QTL × 环境相互作用，并且几个基因组区域涉及 QTL × QTL 相互作用，这些区域未被鉴定为加性 QTL。这些鉴定出的 QTL 与与 N2 固定相关的基因组区域和先前研究中鉴定的其他生理特征共定位。对候选基因的搜索导致检测到许多附加和上位 QTL 的根瘤和 N 代谢基因。