Effect of phosphorus deficiency on biomass and root system architecture in diverse Medicago accessions

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Abstract
Introduction: Phosphorus (P) is essential for legume growth and symbiotic nitrogen fixation, yet its low availability in many soils frequently constrains plant productivity. Methods: To evaluate phenotypic and genotypic variation in P efficiency, 200 genetically diverse accessions of the Medicago sativa complex were assessed under high and low P conditions in a greenhouse experiment, followed by detailed root system architecture (RSA) analysis in a subset of 20 accessions using a rhizotron system. Results: Significant intraspecific variation was observed for shoot and root dry matter, root-to-shoot ratio, shoot P content, and P utilisation efficiency (PUE). Across the full panel of 200 accessions, shoot and root dry matter decreased by 24% and 23% respectively under low P, and in the subset of 20 accessions PUE increased by 38% under low P. Genome-wide association studies identified candidate genes associated with plant height and biomass related traits under high and low P conditions including genes involved in cell-wall modification, hormonal regulation, and growth-related stress responses. Rhizotron analyses revealed RSA plasticity, with increased specific root length and specific convex hull area under low P, reflecting morphological adjustments that enhance soil exploration. Discussion: Accessions that combined stable biomass production, high PUE, and adaptive RSA features under low P represent valuable genetic resources for breeding nutrient-efficient alfalfa cultivars suitable for low-input agricultural systems.
Funding Information
  • Bundesministerium für Ernährung und Landwirtschaft

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