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

item NELSON, P
item COLES, N
item Holland, Jim - Jim
item BUBECK, D
item SMITH, S

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/9/2008
Publication Date: 9/15/2008
Citation: Nelson, P., Coles, N., Holland, J.B., Bubeck, D., Smith, S., Goodman, M. 2008. Molecular Characterization of Maize Inbreds with Expired U.S. Plant Variety Protection. Crop Science. 48:1673-1685.

Interpretive Summary: Understanding the genetic diversity of the US corn crop and the relationship among inbred lines used to produce commercial hybrids is critical to efforts to enhance the genetic base of this crop. Such studies are essentially impossible to conduct with current inbreds because they are covered as intellectual property by the companies that develop them. Inbreds that have been registered for Plant Variety Protection in the USA, however, become publicly available 20 – 25 years after they are registered. The first set of lines that were registered in this way have recently become available publicly and are now amenable to study. We obtained 92 such inbred lines and used DNA fingerprinting techniques to study their relationships and diversity. We found that they group into six major clusters, five of which are represented by public inbred lines. The sixth group represents a unique genetic group that was developed by a single company and was not previously accessed by other breeding programs. We also discovered that there are no unique gene types in the proprietary inbred lines that are absent from a diverse sample of public inbred lines. Improvement of proprietary inbred lines was accomplished not by introduction of unique genes, but by producing improved combinations of genes already present in the public inbred line set.

Technical Abstract: Maize inbred lines with expired Plant Variety Protection Act (PVPA) certificates are publically 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 relationship and population structure among 92 ex-PVPA inbred lines in relation to 18 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 unknown 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. All alleles present in the ex-PVPA inbreds, for the 614 SNP included in this study, are also found in public temperate maize germplasm.