Advancement of Maize Germplasm Improvement and Relevant Research

Scarcity of available germplasm with good quality,stress tolerance,higher combining ability and mega-environment adaptation has been being the bottle-neck in commercial maize breeding program since 1970's.The genetic vulnerability of maize germplasm used in the development of commercial hybrids has been realized,and germplasm enhancement,improvement and development have been an important activity in maize breeding efforts.This review summarizes the germplasm collection,evaluation,improvement and utilization in CIMMYT and USA maize breeding program.Research progress on genetic diversity,heterotic groups and patterns,theory and technology of population improvement,and nature of heterosis are reviewed.The concepts of heterotic alignments by Hallauer in 2003 extended the utilization of the concepts of heterotic patterns to tropical and sub-tropical germplasm improvement from temperate maize breeding efforts,and established a theorical and methodological foundation for maize geremplasm enhancement,improvement and development.Reciprocal recurrent selection inter populations is the key step to use exotic germplasm and land races in development of hybrids.