WITHIN THE LAST FIFTY YEARS, PALMER AMARANTH (AMARANTHUS PALMERI) HAS RISEN FROM RELATIVE INSIGNIFICANCE TO BECOME ONE OF THE MOST ECONOMICALLY DAMAGING AGRONOMIC WEEDS IN THE UNITED STATES. NATIVE TO THE ARID SOUTHWEST, PALMER AMARANTH IS NOW WIDELY DISTRIBUTED THROUGHOUT THE CENTRAL AND SOUTHEASTERN US; AREAS FAR REMOVED FROM ITS NATIVE RANGE AND WHERE HERBICIDE-RESISTANT POPULATIONS POSE SIGNIFICANT CHALLENGES TO ROW CROPS. RECENT DISCOVERIES OF PALMER AMARANTH POPULATIONS AT NEW NORTHERLY LOCATIONS IN TWO MAJOR, GEOGRAPHICALLY DISTINCT, CROP PRODUCTION AREAS OF THE UPPER MIDWEST AND CALIFORNIA'S CENTRAL VALLEY SIGNAL A LOOMING THREAT TO GROWERS IN THESE REGIONS. GROWERS IN AREAS NOT YET FAMILIAR WITH PALMER AMARANTH WILL FACE THE DUAL CHALLENGE OF DETERMINING WHETHER THEY HAVE THIS WEED AND TAKING EFFECTIVE ACTION EARLY TO CONTROL IT. MISTAKING PALMER AMARANTH FOR WIDESPREAD RELATED AMARANTHUS SPECIES COULD PROVE COSTLY. FOR EXAMPLE, EVEN WITH A CONSERVATIVE ESTIMATE OF $10 PER ACRE IN INCREASED COST OF CONTROL, OR ONE ADDITIONAL HERBICIDE APPLICATION, THE POTENTIAL ECONOMIC COST IS STAGGERING (ESTIMATES RUN NEARLY A QUARTER OF A BILLION DOLLARS IN ILLINOIS ALONE). MOREOVER, IF PALMER AMARANTH IS NOT RECOGNIZED EARLY BY PRODUCERS, AND THEREFORE NOT MANAGED PROPERLY, RESULTANT YIELD LOSSES COULD EXCEED $10 PER ACRE BY 10-FOLD OR MORE, RESULTING IN AN EVEN MORE DRAMATIC ECONOMIC IMPACT.NORTHERN RANGE EXPANSION RAISES THE STAKES FOR GROWERS AND WEED MANAGERS AS NEW INVASIONS BY PALMER AMARANTH MIGHT BRING IN PRE-ADAPTED FORMS AND/OR CREATE OPPORTUNITIES FOR NEW ADAPTATIONS. ALL THE MORE WORRISOME IS THAT THIS WEED HAS EVOLVED RESISTANCE TO ALL MAJOR HERBICIDE GROUPS THAT ARE AVAILABLE TO GROWERS OF IMPORTANT ROW CROPS IN THESE AREAS. HOWEVER, RESISTANCE MECHANISMS AND FREQUENCY ARE NOT UNIFORM ACROSS THIS SPECIES' RANGE AND CAN VARY BY POPULATION AND WITHIN INDIVIDUAL PLANTS, THUS COMPLICATING MANAGEMENT DECISIONS. EVIDENCE FROM PRIOR STUDIES WITH OTHER WEED SPECIES SUGGESTS A POSSIBLE LINKAGE BETWEEN CERTAIN HERBICIDE RESISTANCE MECHANISMS AND OTHER POTENTIALLY ADAPTIVE TRAITS SUCH AS DORMANCY AND STRESS TOLERANCE. WHETHER CERTAIN ADAPTIVE TRAITS HAVE PREDISPOSED INDIVIDUALS TO EVOLVING HERBICIDE RESISTANCE, OR VISE-VERSA, IS UNKNOWN AT PRESENT IN PALMER AMARANTH AND IS A GUIDING QUESTION IN OUR PROJECT. ADDITIONALLY, WE ARE PROPOSING A DETAILED EXAMINATION OF INTRASPECIFIC VARIATION IN ECOPHYSIOLOGICAL TRAITS THAT WILL IDENTIFY WHETHER LOCAL ADAPTATION OR PLASTICITY IS FACILITATING INVASION IN DIFFERENT GEOGRAPHIC LOCATIONS AND CROPPING SYSTEMS, WHICH WILL INFORM LOCAL, STATE, AND REGIONALLY-BASED WEED MANAGEMENT INITIATIVES.OUR LONG-TERM GOAL IS TO CONTRIBUTE TO THE DEVELOPMENT OF MORE ENVIRONMENTALLY-SOUND WEED MANAGEMENT STRATEGIES BY UNDERSTANDING HOW WEEDS ADAPT TO EXISTING STRATEGIES. OUR EMPHASIS ON FUNDAMENTAL BIOLOGICAL QUESTIONS, AS THEY RELATE TO KEY KNOWLEDGE GAPS IN PATTERNS OF GENETIC DIVERSITY IN WEED POPULATIONS AND THEIR INFLUENCE ON INVASION SUCCESS AND HERBICIDE RESISTANCE EVOLUTION, IS AN ESSENTIAL STEP TO ACHIEVE THIS GOAL. SPECIFICALLY, OUR OBJECTIVES ARE TO:1. INVESTIGATE THE GENETIC DIVERSITY AND CONNECTIVITY IN POPULATIONS OF PALMER AMARANTH ACROSS SPATIAL AND TEMPORAL SCALES IN NORTH AMERICA TO TRACE THE ORIGIN AND PROGRESSION OF TWO INDEPENDENT AGRICULTURAL INVASIONS IN EAST/MIDWEST NORTH AMERICA AND CENTRAL CALIFORNIA.2. EVALUATE NEUTRAL VS ADAPTIVE (HERBICIDE RESISTANCE GENE) MARKER DATA TO TRACE THE ORIGIN AND SPREAD OF A PARTICULAR SUITE OF AGRICULTURALLY ADAPTIVE TRAITS (HERBICIDE RESISTANCE MUTATIONS) IN PALMER AMARANTH.3. CONDUCT ECOPHYSIOLOGICAL AND GENETIC ASSOCIATION STUDIES OF PALMER AMARANTH POPULATIONS FROM DIFFERENT PARTS OF THE SPECIES' RANGE TO DETERMINE WHETHER ONGOING INVASION IS BEING SHAPED BY CONTINUING LOCAL ADAPTATION TO DIFFERENT CLIMATIC CONDITIONS, EDAPHIC CHARACTERISTICS, OR MANAGEMENT PRACTICES.IN ADDITION TO BEING OF TIMELY AND PRACTICAL RELEVANCE, THE RESEARCH PROPOSED HEREIN IS UNIQUE IN THAT IT TAKES ADVANTAGE OF THE OPPORTUNITY TO INVESTIGATE A WEED INVASION IN REAL-TIME. THE INDEPENDENT INVASIONS OF PALMER AMARANTH INTO THE UPPER MIDWEST AND CENTRAL CALIFORNIA ARE HAPPENING RIGHT NOW, SO NOW IS THE TIME TO STUDY THEIR GENETIC UNDERPINNINGS. RAISING AWARENESS OF PALMER AMARANTH AND THE DEVASTATION IT CAN CAUSE TO CROP PRODUCTION IS A CRITICALLY IMPORTANT STEP TOWARD IMPLEMENTATION OF PROACTIVE RATHER THAN REACTIVE MANAGEMENT STRATEGIES. OUR INTERDISCIPLINARY APPROACH USES CUTTING-EDGE GENOMIC TECHNOLOGY, COMBINED WITH PROVEN MOLECULAR AND GREENHOUSE-BASED METHODS AND EVOLUTIONARY THEORY, TO INVESTIGATE NIFA PROGRAM AREA PRIORITIES INCLUDING FUNDAMENTAL ASPECTS OF WEED BIOLOGY, POPULATION GENETICS, AND THE INFLUENCE OF AGRONOMIC PRACTICES ON WEED POPULATIONS. OUR ACTIVITIES WILL GENERATE NEW INFORMATION THAT WILL INTEGRATE WITH EXISTING DATASETS TO PROVIDE NOVEL INSIGHTS INTO THE SOURCE OF WEEDY INVASIVES AND THE POTENTIAL FOR FURTHER ADAPTATION AS THIS SPECIES CONTINUES TO INVADE NEW ENVIRONMENTS. FURTHERMORE, RESULTS COULD POTENTIALLY BE USED TO IDENTIFY DEMOGRAPHICALLY AND GENETICALLY INDEPENDENT POPULATIONS ON WHICH LOCAL MANAGEMENT EFFORTS CAN BE FOCUSED.