Genetic and Phenotypic Characterization of Maize Germplasm Resources: Ex-PVPA Inbreds, NCSU Inbreds, and Elite Exotic Inbreds

Abstract

ABSTRACT NELSON, PAUL THOMAS. Genetic and Phenotypic Characterization of Maize Germplasm Resources: Ex-PVPA Inbreds, NCSU Inbreds, and Elite Exotic Inbreds. (Under the direction of Major M. Goodman.) Maize (Zea maize L.) germplasm resources are characterized to illuminate their usefulness and proper placement for temperate maize breeding. Three germplasm pools are examined: 1) maize inbreds that have expired U.S. plant variety protection certificates (Ex-PVPA), 2) the North Carolina State University maize inbred line releases, and 3) elite unadapted tropical maize inbreds. We have used single nucleotide polymorphism (SNP) markers to evaluate the relationships and population structure among 92 ex-PVPA inbred lines in relation to 17 well-known public inbreds. Based on UPGMA clustering, principal component analysis, and model-based clustering, we identified six primary genetic clusters represented by the prominent inbred lines B73, Mo17, PH207, A632, Oh43, and B37. We also determined the genetic background of ex-PVPA inbreds with conflicting, ambiguous, or undisclosed pedigrees. We assessed genetic diversity across subsets of ex-PVPA lines and concluded that the ex-PVPA lines are no more diverse than the public set evaluated here. The NCSU maize breeding germplasm represents a potentially useful resource for maize improvement and diversity in the U.S. While the NC maize inbreds can generally be classified into five germplasm pools, Lancaster, temperate-adapted all-tropical (TAAT), Lancaster × Tropical, Stiff Stalk, and Southern non-Stiff Stalk, analysis of detailed pedigree records and with molecular markers reveals additional substructure within each of these pools. There is general agreement among the four cluster analyses performed, three on SNP data and one on pedigree-derived coefficients of coancestry, as to the organization of this substructure. We performed topcross yield trial evaluation for 128 elite tropical maize inbreds from these institutions and 15 temperate-adapted all-tropical NC maize inbreds. We report, not only performance for yield and other traits of agronomic importance, but also heterotic patterns among many of these lines. We maintain, as reported in previous studies conducted at NCSU, that tropical germplasm, either adapted or unadapted, generally combines equally well with either Stiff Stalk or non-Stiff Stalk U.S. maize germplasm.