Adaptation of Plasmid‐ ID Technology for Evaluation of N ₂ ‐Fixing Effectiveness and Competitiveness for Root Nodulation in the Sinorhizobium–Medicago System

Maximising the nitrogen fixation occurring in rhizobia‐legume associations represents an opportunity to sustainably reduce nitrogen fertiliser inputs in agriculture. High‐throughput measurement of symbiotic traits has the potential to accelerate the identification of elite rhizobium/legume associations and enable novel research approaches. Plasmid‐ID technology, recently deployed in Rhizobium leguminosarum , facilitates the concurrent assessment of rhizobium nitrogen‐fixing effectiveness and competitiveness for root nodulation. This study adapts Plasmid‐ID technology to function in Sinorhizobium species that are central models for studying rhizobium‐legume associations and form economically important symbioses with alfalfa. New Sino‐Plasmid‐IDs were developed and tested for stability and their ability to measure competitiveness for root nodulation and nitrogen‐fixing effectiveness. Rhizobial competitiveness is measured by identifying strain‐specific nucleotide barcodes using next‐generation sequencing, whereas effectiveness is measured by GFP fluorescence driven by the synthetic nifH promoter. Sino‐Plasmid‐IDs allow researchers to efficiently study competitiveness and effectiveness in a multitude of Sinorhizobium strains simultaneously.