**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** THIS 'STANDARD' RESEARCH PROJECT BEST ALIGNS WITH THE PROGRAM AREA 'CHARACTERISTICS, RATES, AND MECHANISMS OF GENE TRANSFER TO WILD RELATIVES'. THE OVERARCHING GOAL OF THIS PROJECT IS TO DEVELOP A THOROUGH UNDERSTANDING OF THE FREQUENCY OF GENE FLOW AND HYBRID FITNESS BETWEEN CROP SORGHUM AND JOHNSONGRASS WHEN JOHNSONGRASS SERVES AS THE FEMALE PARENT, TO PROVIDE NECESSARY SCIENTIFIC DATA FOR FEDERAL REGULATORY AGENCIES TO ASSIST WITH DECISION MAKING AND ALSO HELP IDENTIFY AVENUES FOR MITIGATING GENE FLOW. THE SPECIFIC OBJECTIVES ARE: 1. DETERMINE THE FREQUENCY OF 2N GAMETE PRODUCTION IN S. BICOLOR POLLEN AS INFLUENCED BY GENOTYPE (BOTH POLLINATORS AND HYBRIDS); 2. DETERMINE THE FREQUENCY OF S. HALEPENSE X S. BICOLOR HYBRIDIZATION AS INFLUENCED BY DISTANCE FROM POLLEN SOURCE; 3. ELUCIDATE BACKCROSSING POTENTIAL OF F1 PROGENY WITH EITHER PARENTS (S. HALEPENSE AND S. BICOLOR); 4. UNDERSTAND HYBRID CHARACTERISTICS AND FITNESS OF F1 AND BC1F1 PROGENY OF S. HALEPENSE X S. BICOLOR: A) WITH FITNESS-NEUTRAL HERBICIDE-RESISTANT TRAITS UNDER FIELD CONDITIONS, B) WITH TRANSGENIC COMPOSITIONAL TRAITS UNDER GREENHOUSE CONDITIONS; AND 5. UNDERSTAND HYBRID CHARACTERISTICS AND FITNESS OF F1 AND BC1F1 PROGENY OF SHATTERCANE (S. BICOLOR SSP. DRUMMONDII) X TRANSGENIC S. BICOLOR UNDER GREENHOUSE CONDITIONS. OVERALL, FINDINGS WILL HELP IMPROVE THE EXISTING RISK ASSESSMENT FRAMEWORKS BY PROVIDING VALUABLE INFORMATION REGARDING THE RISK OF GENE FLOW FROM SORGHUM TO JOHNSONGRASS (BOTH NON-TRANSGENIC HERBICIDE RESISTANCE AND TRANSGENIC LIGNIN MODIFICATION TRAITS), PROVIDE INSIGHTS ON THE DISTANCE OF POLLEN-MEDIATED GENE FLOW, AND ILLUSTRATE FITNESS CHARACTERISTICS OF THE F1 AND BC1F1 PROGENY OBTAINED WITH JOHNSONGRASS AND SHATTERCANE.