Crimson clover (Trifolium incarnatum L.) is the most common legume cover crop in the United States. Previous research found limited genetic variation for crimson clover within the National Plant Germplasm System (NPGS) collection. The aim of this study was to assess the phenotypic and nodule microbial diversity within the NPGS crimson clover collection, focusing on traits important for cover crop performance. Experiments were conducted at the Beltsville Agricultural Research Center (Maryland, USA) across three growing seasons (2012–2013, 2013–2014, 2014–2015) to evaluate 37 crimson clover accessions for six phenotypic traits: fall emergence, winter survival, flowering time, biomass per plant, nitrogen (N) content in aboveground biomass, and proportion of plant N from biological nitrogen fixation (BNF). Accession effect was significant across all six traits. Fall emergence of plant introductions (PIs) ranged from 16.0% to 70.5%, winter survival ranged from 52.8% to 82.0%, and growing degree days (GDD) to 25% maturity ranged from 1470 GDD to 1910 GDD. Biomass per plant ranged from 1.52 to 6.51 g, N content ranged from 1.87% to 2.24%, and proportion of plant N from BNF ranged from 50.2% to 85.6%. Accessions showed particularly clear differences for fall emergence and flowering time, indicating greater diversity and potential for selection in cover crop breeding programs. Fall emergence and winter survival were positively correlated, and both were negatively correlated with biomass per plant and plant N from BNF. A few promising lines performed well across multiple key traits, and are of particular interest as parents in future breeding efforts, including PIs 369045, 418900, 561943, 561944, and 655006. In 2014–2015, accessions were also assessed for nodule microbiome diversity, and 11 genera were identified across the sampled nodules. There was large variation among accessions in terms of species diversity, but this diversity was not associated with observed plant traits, and the functional implications of nodule microbiome diversity remain unclear.

中文翻译：

---

绯红色三叶草（Trifolium incarnatum L.）材料之间的表型和根瘤微生物多样性

深红色的三叶草（三叶草L.）是美国最常见的豆科植物。先前的研究发现国家植物种质系统（NPGS）集合中的深红色三叶草的遗传变异有限。这项研究的目的是评估NPGS深红色三叶草收藏品中的表型和根瘤微生物多样性，重点研究对覆盖农作物性能重要的性状。在美国贝尔茨维尔农业研究中心（美国马里兰州）的三个生长季节（2012-2013年，2013-2014年，2014-2015年）进行了实验，评估了37个深红色三叶草的6个表型性状：秋季出苗，冬季存活，开花时间，每株植物的生物量，地上生物量中的氮（N）含量以及来自生物固氮（BNF）的植物N的比例。在所有六个性状中，加入效应均显着。植物引种（PIs）的秋季出苗率从16.0％到70.5％，冬季成活率从52.8％到82.0％，成年日数（GDD）到25％的成熟度从1470 GDD到1910 GDD。每株植物的生物量为1.52至6.51 g，氮含量为1.87％至2.24％，BNF中植物氮的比例为50.2％至85.6％。种质在秋季出苗和开花时间方面表现出特别明显的差异，这表明更大的多样性和在覆盖作物育种计划中的选择潜力。秋季出苗和冬季存活率与BNF的单株生物量和植物N均呈负相关。一些有希望的品系在多个关键性状上表现良好，作为父母对未来育种工作特别感兴趣，包括PI 369045、418900、561943、561944和655006。在2014–2015年，还评估了种质的结核微生物组多样性，并在采样的结核中鉴定了11个属。不同物种之间的物种多样性差异很大，但这种多样性与观察到的植物性状无关，而且根瘤微生物组多样性的功能含义仍不清楚。