Molecular Characterization of Maize Inbreds with Expired U.S. Plant Variety Protection.

Maize inbred lines with expired Plant Variety Protection Act (PVPA) certificates are publicly available and potentially represent a new germplasm resource for many public and private breeding programs.  However, accurate pedigree and genetic background information for ex-PVPA maize inbreds is necessary if they are to be effectively utilized in breeding efforts.  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.  Additionally, all alleles present in the ex-PVPA inbreds, for the 614 SNP included in this study, are also found in public temperate maize germplasm.