Phenotypic and nodule microbial diversity among crimson clover (Trifolium incarnatum L.) accessions

Authors: MOORE, VIRGINIA - North Carolina State University; DAVIS, BRIAN - University Of Maryland; Maul, Jude; Kucek, Lisa; Mirsky, Steven

Submitted to: Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/8/2020
Publication Date: 9/21/2020
Citation: Moore, V., Davis, B., Maul, J.E., Kucek, L.K., Mirsky, S.B. 2020. Phenotypic and nodule microbial diversity among crimson clover (Trifolium incarnatum L.) accessions. Agronomy. 10(9):1434. https://doi.org/10.3390/agronomy10091434.
DOI: https://doi.org/10.3390/agronomy10091434

Interpretive Summary: 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, but the crimson clover populations in the collection have not been evaluated for performance of traits important for cover cropping. For three growing seasons, we tested 37 crimson clover populations for fall emergence, winter survival, flowering time, biomass production, nitrogen (N) content in aboveground biomass, and proportion of plant N from biological nitrogen fixation (BNF). Populations showed the strongest differences for fall emergence and flowering time, indicating greater diversity and potential for selection in cover crop breeding programs. Populations were also assessed for nodule microbiome diversity, and showed large variation in terms of microbe species present. However, the impact of this species diversity on cover crop performance is unclear.

Technical Abstract: 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.