Breeding Potential of Exotic Maize Populations to Improve an Elite Chinese Hybrid

Published in Agron. J. 105:1555–1564 (2013) doi:10.2134/agronj2013.0050 Copyright © 2013 by the American Society of Agronomy, 5585 Guilford Road, Madison, WI 53711. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. T Yellow and Huai river valleys in the Corn Belt constitute the second largest maize-producing region in China, representing about 33% of the national maize production area and 36% of the total maize production (Li, 2009; Zhang and Bonjean, 2010). The maize cultivars grown predominantly in this region have changed six times since the 1950s (Ci et al., 2013). Maize yield in China has substantially increased since the 1970s, when single-cross hybrids (starting with the hybrid Xindan 1) were released (Ci et al., 2011). Commercial hybrids in this region have mainly been developed by crossing elite lines belonging to Group PA (derived from U.S. Pioneer hybrids) and Sipingtou (a Chinese local landrace and its derivatives) (Yuan et al., 2001; Xie et al., 2007; Zhang and Bonjean, 2010). Among these hybrids, an elite single-cross hybrid, Zhengdan958 (Zheng 58 Chang 7-2), representing the predominant heterotic Group PA Sipingtou, was released in 2004 and has since become the most widely planted hybrid. In recent years, however, poor performance due to decreased yield potential and poor grain quality has gradually become more frequent. Numerous efforts have been made to improve this hybrid; however, there is no Chinese germplasm from the two heterotic groups, PA and Sipingtou, that possesses favorable alleles for improving Zhengdan958, which still yields significantly higher than other cultivars tested so far. Introgressing useful genetic variability from exotic germplasm into these two adapted heterotic pools has become an important strategy (Zhang and Bonjean, 2010). In 1996, an important national research project, the Maize Germplasm Enhancement, Improvement, and Development, was initiated by the Chinese Academy of Agricultural Sciences (CAAS), similar to the Latin American Maize Project (LAMP) (Salhuana et al., 1991) and the Germplasm Enhancement of Maize (GEM) project (Salhuana et al., 1994), to introgress genes from exotic germplasm into the current Chinese breeding germplasm. Each 1% increase in the genetic contribution of exotic germplasm from CGIAR and the United States has increased maize yield in China by 0.025 and 0.01 Mg ha–1, respectively (Li et al., 2006). In addition, the exotic germplasm is changing the maize cropping system in China. For example, U.S. temperate germplasm with lower ear height, shorter maturity, and high harvest index was introduced and improved, resulting in a gradual increase in plant population density and therefore mechanized harvesting of the maize crop (Shi, 2007; Hallauer and Carena, 2009). Strong root systems and stay-green traits AbstRAct Introgression of favorable alleles from exotic maize (Zea mays L.) germplasm can broaden the narrow genetic base of available temperate germplasm. Development of maize hybrids for the Yellow and Huai river valleys in the Corn Belt of China has always been hampered by the lack of favorable alleles for improving maize yield and quality. Twenty exotic populations from CIMMYT and the United States were evaluated to identify alleles for improving a widely cultivated hybrid, Zheng 58 Chang 7-2, which represents the predominant heterotic group, PA Sipingtou. Sixty-three genotypes, comprising 20 populations, two inbred lines (Zheng 58 and Chang 7-2), a single-cross hybrid (Zheng 58 Chang 7-2), and 40 inbred population crosses between the parental inbreds and the CIMMYT and U.S. populations were evaluated for grain yield, test weight, and ear height. Several populations from CIMMYT and the United States were identified as potential sources of favorable alleles for traits lacking in the elite hybrid, Zheng 58 Chang 7-2, for each trait evaluated. Two exotic populations, Pop 49 and Stay green-yellow, were the most outstanding because they possessed favorable alleles for several traits that were not present in the target hybrid evaluated. These results demonstrate that the exotic populations evaluated in this study represent sources of useful genetic variability with good potential for improving Chinese elite germplasm.