Heterosis Decreasing in Hybrids: Yield Test Inbreds

for inbred or cultivar yields, heterosis yields, and hybrid yields along with percentage heterosis across years of time periods. Duvick (1984, 1999) and Duvick et al. (2004) summa-rized data on Pioneer Hi-Bred International (PHBI; Johnston, IA) commercial hybrids introduced in central Iowa across fi ve decades. ................
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