Changes in yield and yield components of single-cross maize hybrids released in China between 1964 and 2001

The objectives of this study were to (i) measure genetic gain using a set of maize (Zea mays L.) single-cross hybrids that were widely used in Chinese maize production from 1964 to 2001, (ii) determine if there were changes in morphological characteristics, and (iii) examine the germplasm backgrounds of these hybrids. Yield trials were conducted for 3 yr, using a split-plot design. Each hybrid was planted at three different densities in four locations, two locations each representing summer and spring corn areas. Mean rates of genetic gain were 52 kg ha -1 yr -1 when measured at the spring locations, 69 kg ha -1 yr -1 when measured at the summer locations, and 60 kg ha -1 yr -1 when measured across all locations. There was no significant effect of planting density on genetic gain. Genetic gain has been largely contributed by increased yield per plant and this strategy was reflected in changes in ear and plant morphology. Analyses of pedigree backgrounds showed continuing dependence on U.S. germplasm backgrounds, notably C103, Oh43, Mo17, and Iowa Stiff Stalk Synthetic (BSSS).