Genetic Contribution to Advanced Yield for Maize Hybrids Released from 1970 to 2000 in China

Four to five cycles of maize (Zea mays L.) hybrid replacement have occurred in China since the 1970s. Retrospective analyses of genetic yield may provide an understanding of unexploited genetic potential and indicate pathways for future yield improvement. The objective of this study was to assess genetic gains in grain yield, especially those due to increased tolerance to stress in China from the 1970s through the 2000s. Trials were conducted at two locations per year and three densities per location during the 2005-2006 (Exp. 1) and 2007-2008 (Exp. 2) growing seasons. Over a 40-yr period, the genetic gain in yield averaged 94.7% kg ha(-1) per year and 53% of this was attributable to breeding undertaken in China. The newer hybrids showed increased tolerance to compound stress. We estimated that the contribution of stress tolerance to genetic yield gain was equal to 46 or 74% at 60,000 or 75,000 plants ha(-1), respectively. Yield improvement has occurred at a slow pace at densities of 60,000 and 75,000 plants ha(-1) in China. Further increasing maize grain yield in China will be achieved through higher plant populations, and this will require breeding for greater stress tolerance.