Genetic variation in host selectivity and adaptive strain enrichment in legume-rhizobia symbiosis

Mutualism breakdown can be prevented if partner species preferentially select and reward partners that provide greater benefit. We examined these two components using the legume Medicago truncatula and its nitrogen-fixing symbiont Sinorhizobium meliloti. The first dataset focuses on reanalyzing strain composition data from the nodules of 202 accessions to show significant genetic variation in the capacity of Medicago to restrict strain diversity when controlling for nodule number variation using a simulation. By performing an augmented image analysis of nodules pool images to produce scores of morphological parameters, we found that hosts with a suite of nodules traits, including shorter nodules, tended to be more selective. Using previously published SNP data for these ~200 accessions, we performed a genome-wide association study on host selectivity to identify candidate genes. The second dataset uses two well-studied Medicago genotypes (A17 and R108) with contrasting nodule morpholog..., , # Genetic variation in host selectivity and adaptive strain enrichment in legume-rhizobia symbiosis

This Dryad Repository supports and enables the reuse of Burghardt et al. 2026 data and associated analysis outputs, including raw phenotypic data, software, analysis code, and GWAS and statistical outputs.

This repository included three major parts: 1) data and analysis of *Medicago* **host selectivity** and **nodule morphology** of 202 accessions of Medicago inoculated with a mixture of  86 *Sinorhizobium meliloti* strains. We provide code to assess how host selectivity is correlated with nodule morphology traits using LASSO regression and Boruta. 2) Results from a **genome-wide association analysis** of the host selectivity trait, and 3) data and analysis of *Medicago* **adaptive enrichment** of bacterial symbionts. The adaptive enrichment analysis includes measuring symbiotic traits (nodule length, size, branching, colony-forming units, nodule number, and strain relative frequencie...,