** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** ROOT-KNOT NEMATODES ARE HIGHLY EVOLVED OBLIGATE PARASITES THAT THREATEN GLOBAL FOOD SECURITY. THESE NEMATODES HAVE A REMARKABLE ABILITY TO MODIFY HOST CELLS THAT SERVE AS THEIR ONLY SOURCE OF NUTRIENTS THROUGHOUT THEIR LIFE CYCLE. RESISTANCE TO ROOT-KNOT NEMATODES CONFERRED BY THE SINGLE DOMINANT GENE MI-1 IS AVAILABLE IN MANY VARIETIES OF FRESH AND PROCESSING TOMATOES. HOWEVER, AN INCREASED RELIANCE ON MI-1 DUE TO LIMITED AVAIALBILITY OF NEMATICIDES HAS LED TO THE EMERGENCE OF RESISTANCE-BREAKING NEMATODE POPULATIONS IN TOMATO FIELDS. THE SPECIFIC AIM OF THIS PROPOSAL IS TO USE COMPARATIVE GENOMICS TO ELUCIDATE THE GENETIC MECHANISMS AND IDENTIFY GENETIC FACTORS THAT CONTRIBUTE TO ROOT-KNOT NEMATODES OUTBREAKS IN RESISTANT TOMATO FIELDS. OUR PRELIMINARY DATA SHOW THAT RESISTANCE-BREAKING NEMATODES ARE LESS FIT ON SUSCEPTIBLE TOMATO AND HAVE REDUCED HOST RANGE. WE WILL INVESTIGATE THE GENETIC FACTORS THAT CONTRIBUTE TO THIS FITNESS COST. LASTLY, WE WILL DEVELOP A RAPID RELIABLE METHOD TO IDENTIFY RESISTANCE-BREAKING ROOT-KNOT NEMATODES ISOLATES FROM FIELDS. THE AVAILABILITY OF DIAGNOSTIC TOOLS WILL FACILITATE THE DEVELOPMENT OF ALTERNATIVE MANAGEMENT STRATEGIES INCLUDING THE IDENTIFICATION OF APPROPRIATE ROTATION CROPS. OVERALL, THE PROJECT WILL CONTRIBUTE TO THE DEVELOPMENT OF MUCH-NEEDED ENVIRONMENTALLY SAFE NEMATODE CONTROL STRATEGIES. THE GOAL OF PROPOSED RESEARCH IS DIRECTLY RELEVANT TO THE GOALS AND PRIORITIES OF THE AGRICULTURE AND FOOD INITIATIVE (AFRI), WHICH SUPPORTS RESEARCH DIRECTED AT THE LONG-TERM IMPROVEMENT AND SUSTAINABILITY OF U.S. AGRICULTURAL AND FOOD SYSTEMS.