2012 Annual Report 1a.Objectives (from AD-416): Genetically characterize yield heterotic effects in an elite Upland x elite Upland cotton cross. 1b.Approach (from AD-416): Previously, a NC Design III backcross mapping population was constructed from 286 F2 plants derived from an elite-by-elite Upland cotton cross known to exhibit large yield heterosis. DNA was extracted from each F2 plant and approximately 580 NC Design III progeny rows were seed increased. The 286 F2 plants will be genotyped with molecular markers deemed polymorphic between the elite Upland parental lines. A molecular linkage map will be constructed. Also, the NC Design III progeny rows will be evaluated for yield, yield component traits, and fiber quality traits in field trials conducted in South Carolina, Louisiana, and Arizona. Heterotic effects for these traits will be calculated. Finally, the molecular linkage map and field data will be used in a quantitative trait loci (QTL) analysis to identify genomic regions associated with heterotic effects for yield, yield component, and fiber quality traits. 3.Progress Report: This project is related to objective 2 of the in-house project: to develop new cotton genetic resources with improved fiber quality, lint yield stability, and adaptation. Knowledge of the genetic architecture of heterosis could facilitate efforts to substantially increase yield. The primary objective of this cooperative research project is to genetically characterize yield heterotic effects (hybrid vigor) in upland cotton. During 2011, a large, bi-parental genetic population segregating for yield heterosis effects was constructed. Seed of nearly 600 total genetic offspring was increased to facilitate multi-year field tests. DNA was extracted from each member of the genetic population. ARS-New Orleans used the DNA to genotype or type each member of the population with nearly 400 DNA markers in order to construct a genetic linkage map. The genetic population is currently being evaluated in field trials located in South Carolina, Arizona (ARS-Maricopa), and Louisiana (Louisiana State University). In the near future, a genetic linkage map will be constructed and the agronomic data collected from each field trial will be used in an analysis to identify specific chromosomal regions associated with yield heterosis. This research will facilitate the exploitation of heterosis as a strategy to increase yield in contemporary cotton breeding programs.