Increasing Maize Productivity in China by Planting Hybrids with Germplasm that Responds Favorably to Higher Planting Densities.

We compared yield, genetic gain, and morphology for two sets of maize (Zea mays L.) hybrids using yield test plots grown in China at different pianting densities. One set comprised 29 Chinise maize hybrids that were individually widely grown in China during 1964 through 2001. A second set comprised U.S. hybrids that were used either during the 1960s or during the 2000s. The US. hybrids had higher yields for both 1960s and 2000s comparisons. United States hybrids showed highest genetic gain (81 kg ha^-1) at the highest planting density (67,550 plants ha1) whereas the highest rate of gain for Chinese hybrids was 62 kg ha1 at the medium planting density (52,500 plants ha1). Unlike the Chinese hybrids, U.S. hybrids showed significant interaption with planting density. Chronologically, all hybrids showed morphological changes for many characteristics, often at different rates, and occasionally in different directions. Pedig~ree and molecular marker data showed U.S. and Chinese hybrids to be very different germplasm with decades-old U.S. germplasm contributing even to recently developed and widely used Chinese hybrids. Chinese maize agricultural production can rapidly and significantly benefit from adopting breeding and agronomic strategies that allow for improved yield under higher planting densities. [ABSTRACT FROM AUTHOR]