** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** THE MANUFACTURING AND APPLICATION OF AMMONIA USED IN AMMONIA-BASED FERTILIZERS LEADS TO DEVASTATING EFFECTS ON CLIMATE AND WATER ECOSYSTEMS. AN ALTERNATIVE IS THE RHIZOBIA-LEGUME SYMBIOSIS, WHERE SOIL-DWELLING BACTERIA CONVERT ATMOSPHERIC NITROGEN INTO AMMONIA FOR PLANTS IN RETURN FOR CARBOHYDRATES. RHIZOBIA INOCULANTS ARE USED TO IMPROVE CROP YIELD OF LEGUMES. AN ISSUE WITH THE APPLICATION OF INOCULANTS IS THE RHIZOBIA COMPETITION PROBLEM. INOCULANTS ARE OUT-COMPETED BY INEFFICIENT, CHEATING NATIVE RHIZOBIA. WE HAVE IDENTIFIED A SEGREGATING TRAIT IN ALFALFA THAT ALLOWS THE PLANT TO INHIBIT RELATIONSHIPS WITH A RHIZOBIUM STRAIN THAT SHOWS CHARACTERISTICS OF CHEATING. AIMS OF THIS STUDY INCLUDE I) IDENTIFYING AND VERIFYING THE GENE CAUSING THIS STRAIN-SPECIFIC INTERACTION AND II) INVESTIGATING IF ALFALFA CONTAINING THIS GENE CAN EXERT A SELECTIVE PRESSURE THAT PROMOTES HIGHER POPULATIONS OF EFFICIENT STRAINS IN ROOT NODULES. CANDIDATE GENES WILL BE IDENTIFIED VIA MARKER SEQUENCING AND QTL MAPPING. INTRODUCING CANDIDATE GENES THROUGH HAIRY ROOT TRANSFORMATION INTO NON-SANCTIONING PLANTS WILL VERIFY GENE FUNCTION. THE SELECT-AND-RESEQUENCE TECHNIQUE WILL IDENTIFY POPULATION LEVELS OF EFFECTIVE AND INEFFECTIVE STRAINS WHEN INOCULATED ONTO ALFALFA WITH AND WITHOUT THE GENE. BY IDENTIFYING THIS GENE AND ITS SIGNIFICANCE IN CONTROLLING RHIZOBIA POPULATIONS, WE HOPE TO UNCOVER A WAY FARMERS CAN IMPROVE CROP YIELDS AND MAXIMIZE SUSTAINABILITY BY INCORPORATING VARIETIES OF ALFALFA CONTAINING THIS GENE INTO THEIR CROP ROTATION. THIS PROJECT PROVIDES MULTIPLE TRAINING OPPORTUNITIES THROUGH WORK WITH COLLABORATORS, EXPOSURE TO CAREER OPTIONS, AND FOR EXPERIENCE PRESENTING BY ATTENDING MULTIPLE CONFERENCES.