Soybean Genomics and Improvement Laboratory, USDA-ARS, Beltsville, MD, 20705, USA.
BMC Genomics. 2023 Sep 4;24(1):520. doi: 10.1186/s12864-023-09627-4.
Symbiotic nitrogen fixation differs among Bradyrhizobium japonicum strains. Soybean inoculated with USDA123 has a lower yield than strains known to have high nitrogen fixation efficiency, such as USDA110. In the main soybean-producing area in the Midwest of the United States, USDA123 has a high nodule incidence in field-grown soybean and is competitive but inefficient in nitrogen fixation. In this study, a high-throughput system was developed to characterize nodule number among 1,321 Glycine max and 69 Glycine soja accessions single inoculated with USDA110 and USDA123.
Seventy-three G. max accessions with significantly different nodule number of USDA110 and USDA123 were identified. After double inoculating 35 of the 73 accessions, it was observed that PI189939, PI317335, PI324187B, PI548461, PI562373, and PI628961 were occupied by USDA110 and double-strain nodules but not by USDA123 nodules alone. PI567624 was only occupied by USDA110 nodules, and PI507429 restricted all strains. Analysis showed that 35 loci were associated with nodule number in G. max when inoculated with strain USDA110 and 35 loci with USDA123. Twenty-three loci were identified in G. soja when inoculated with strain USDA110 and 34 with USDA123. Only four loci were common across two treatments, and each locus could only explain 0.8 to 1.5% of phenotypic variation.
High-throughput phenotyping systems to characterize nodule number and occupancy were developed, and soybean germplasm restricting rhizobium strain USDA123 but preferring USDA110 was identified. The larger number of minor effects and a small few common loci controlling the nodule number indicated trait genetic complexity and strain-dependent nodulation restriction. The information from the present study will add to the development of cultivars that limit USDA123, thereby increasing nitrogen fixation efficiency and productivity.
慢生根瘤菌菌株之间的共生固氮作用存在差异。接种 USDA123 的大豆产量低于已知固氮效率高的菌株，如 USDA110。在美国中西部主要的大豆产区，USDA123 在田间生长的大豆中结瘤率很高，具有竞争力但固氮效率低。在这项研究中，开发了一种高通量系统来表征单独接种 USDA110 和 USDA123 的 1321 个大豆和 69 个野生大豆品系的根瘤数量。
鉴定出 73 个大豆品系的 USDA110 和 USDA123 根瘤数量存在显著差异。在双接种这 73 个品系中的 35 个后，观察到 PI189939、PI317335、PI324187B、PI548461、PI562373 和 PI628961 被 USDA110 和双菌株结瘤占据，但不被 USDA123 单菌株结瘤占据。PI567624 仅被 USDA110 结瘤占据，PI507429 限制了所有菌株。分析表明，接种 USDA110 时，35 个位点与大豆的根瘤数量相关，而接种 USDA123 时，35 个位点与大豆的根瘤数量相关。接种 USDA110 时，在野生大豆中有 23 个位点与根瘤数量相关，而接种 USDA123 时，有 34 个位点与根瘤数量相关。在两种处理中仅鉴定出四个共同的位点，每个位点只能解释 0.8%至 1.5%的表型变异。
开发了高通量表型分析系统来表征根瘤数量和占据情况，并鉴定出限制根瘤菌菌株 USDA123 但偏好 USDA110 的大豆种质资源。控制根瘤数量的较小数量的次要效应和少数共同位点表明该性状遗传复杂性和菌株依赖性的结瘤限制。本研究的信息将有助于开发限制 USDA123 的品种，从而提高固氮效率和生产力。
