SWITCHGRASS IS A LEADING HERBACEOUS SPECIES SELECTED FOR BIOENERGY FEEDSTOCK DEVELOPMENT. IT IS ANTICIPATED THAT FEEDSTOCK SWITCHGRASS WILL BE PLANTED IN THE MARGINAL LANDS AND THAT FARMERS CAN GENERATE ADDITIONAL INCOME BY PARTICIPATING IN FEEDSTOCK SWITCHGRASS PRODUCTION. PLANTING SWITCHGRASS HAS SEVERAL ENVIRONMENTAL BENEFITS INCLUDING IMPROVING SOIL HEALTH BY INCREASING ORGANIC MATTER IN SOIL. BIOMASS YIELD OF CURRENT CULTIVARS NEEDS SIGNIFICANT IMPROVEMENT TO IMPROVE THE ECONOMICS OF BIOENERGY PRODUCTION AND TO ALLOW GROWERS TO ACHIEVE REASONABLE INCOMES. BIOMASS YIELD IMPROVEMENT CAN BE ACHIEVED THROUGH REPEATED CYCLES OF SELECTION AND POPULATION IMPROVEMENT OR THROUGH DEVELOPMENT OF HIGH-YIELDING HYBRID CULTIVARS. WITH SWITCHGRASS, HYBRID PRODUCTION FROM INBRED PARENTS IS NOT POSSIBLE BECAUSE IT IS NEARLY 100% SELF-STERILE. IN SUCH SPECIES, CROSSES BETWEEN NON-INBRED GENOTYPES ARE ALTERNATIVE WAYS TO EXPLOIT HYBRID VIGOR OR HETEROSIS. CONVENTIONAL METHODS OF CULTIVAR DEVELOPMENT ARE VERY SLOW, I.E., EACH CYCLE OF SELECTION TAKES ABOUT 4 TO 5 YEARS. IDENTIFICATION OF GENES RESPONSIBLE FOR BIOMASS YIELD HETEROSIS AND DEVELOPMENT OF GENETIC MARKERS LINKED TO THESE GENES WOULD AID TO IMPROVE EFFICIENCY IN HYBRID CULTIVAR DEVELOPMENT IN SWITCHGRASS.THE CHANCE OF FINDING SUPERIOR HYBRIDS IS MORE LIKELY WHEN CROSSES ARE MADE BETWEEN LESS RELATED POPULATION POOLS. WE HYPOTHESIZED THAT TWO SOUTHERN POPULATIONS OF SWITCHGRASS, NAMELY, 'ALAMO' AND 'KANLOW' REPRESENT GENETICALLY DISTINCT POPULATIONS THAT CARRY DIFFERENT SETS OF GENES THAT WHEN COMBINED WOULD PRODUCE SUPERIOR HYBRIDS. WE INTEND TO DEVELOP ALAMO AND KANLOW POPULATIONS INTO TWO DIVERGENT POOLS OF PARENTS FOR USE IN LONG-TERM HYBRID CULTIVAR DEVELOPMENT. SPECIFICALLY, IN THIS STUDY WE PROPOSE TO USE POPULATION OF SWITCHGRASS COMPRISED OF SEVERAL ALAMO &TIMES; KANLOW CROSSES TO MAP GENES AND GENOMIC REGIONS ASSOCIATED WITH SUPERIOR HYBRID PERFORMANCE. THE ALAMO &TIMES; KANLOW CROSSES WERE SELECTED BASED ON SUPERIOR HYBRID PERFORMANCE UNDER GROWING CONDITIONS IN TENNESSEE. EACH OF THESE CROSSES WILL HAVE UNIQUE VARIATION IN GENES THAT CONTRIBUTE TO BIOMASS YIELD AND YIELD WILL BE ASSESSED IN REPLICATED TRIALS UNDER TENNESSEE ENVIRONMENTS. WE WILL CHARACTERIZE VARIATION IN GENOMIC REGIONS ASSOCIATED WITH HIGH AND LOW BIOMASS YIELDING GENOTYPES TO IDENTIFY CANDIDATE GENES CONTROLLING HETEROSIS. MOLECULAR MARKERS WILL BE DEVELOPED FOR USE IN MARKER-ASSISTED SELECTION. FOR THE TWO HIGHEST YIELDING HYBRIDS, SEED WILL BE MULTIPLIED AND HYBRID PERFORMANCE WILL BE CONFIRMED IN MARGINAL ENVIRONMENTS. THE PROPOSED STUDY WILL TRAIN ONE PH.D. STUDENT, ONE RESEARCH ASSOCIATE, AND FIVE PLANT SCIENCE UNDERGRADUATE STUDENTS IN ADVANCED PLANT BREEDING METHODOLOGIES.THIS STUDY WILL GENERATE NEW KNOWLEDGE ON GENETICS UNDERLYING BIOMASS HETEROSIS. CANDIDATE GENES ASSOCIATED WITH BIOMASS HETEROSIS WILL BE IDENTIFIED. MOLECULAR MARKERS WILL BE DEVELOPED WHICH WILL BE DEPLOYED INTO ONGOING ALAMO &TIMES; KANLOW POPULATION IMPROVEMENT. THIS WILL ENHANCE THE EFFICIENCY IN DEVELOPMENT OF HIGH BIOMASS YIELDING HYBRID CULTIVARS OF SWITCHGRASS. RESULTS WILL BE PUBLISHED IN PEER-REVIEWED JOURNALS AND PRESENTED IN ANNUAL MEETINGS OF PROFESSIONAL SOCIETIES. ADAPTATION OF NEW VARIETIES AND THE TRAINING OF NEW CROP BREEDERS WILL CONTRIBUTE TOWARDS SUSTAINABLE SUPPLY OF BIOMASS FEEDSTOCK FOR BIOENERGY PRODUCTION.