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PLANT GENETIC RESOURCES

Pedigree Background Changes in U.S. Hybrid Maize between 1980 and 2004

Pioneer Hi-Bred International, Inc., Crop Genetics Research and Product Development, DuPont Agriculture and Nutrition, 7300 NW 62nd Ave., Box 1004, Johnston, IA 50131-1004

^* Corresponding author: stephen.smith{at}pioneer.com.

Monitoring genetic diversity helps determine whether plant breeders are successful at maintaining germplasm resources sufficient to provide a continued basis for genetic gain and to avoid vulnerabilities potentially associated with a narrowing genetic base. This study used pedigree data of public and proprietary maize (Zea mays L.) inbred lines and sets of Pioneer brand hybrids that were cultivated widely during the period 1980 to 2004 to report on changes in genetic diversity. Pedigree backgrounds for a set of inbred lines bred by different proprietary programs were more diverse (42 founders) than a set of publicly bred inbred lines that were widely used in 1980 (30 founders). Pedigrees of Pioneer hybrids traced to 82 founders. Most of the pedigree backgrounds were contributed collectively by 25 to 50% of the founders. Germplasm was associated into three groups: (i) older public lines, newer proprietary inbreds, and two sets of later maturity Pioneer hybrids; (ii) other later maturity Pioneer hybrids and earlier maturity Pioneer hybrids used in 1980 to 1981; and (iii) remaining early maturity Pioneer hybrids. Differences in proportions of founders already present in U.S. maize germplasm, notably Reid Yellow Dent, Iodent, SMPRS5, Minnesota 13, and Leaming, contributed most as usage changed from older public lines to increased usage of proprietary lines during 1980 to 2004. Changes for Pioneer hybrids involved generally small percentages for several founders, although changes for Reid and Iodent were greater. Future genetic gains are dependent on the deployment of useful genetic diversity. Regular assays of hybrid genetic diversity using molecular markers are recommended.

Abbreviations: PVP, Plant Variety Protection • RFLP, restriction fragment length polymorphism • RM, relative maturity • SSR, simple sequence repeat

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