Agronomy Publications Agronomy 1988 Corn Breeding A. R. Hallauer U.S. Department of Agriculture, [email protected] Wilbert A. Russell Iowa State University K. R. Lamkey U.S. Department of Agriculture, [email protected] Follow this and additional works at: http://lib.dr.iastate.edu/agron_pubs Part of the Agricultural Science Commons, Agronomy and Crop Sciences Commons, and the Plant Breeding and Genetics Commons The ompc lete bibliographic information for this item can be found at http://lib.dr.iastate.edu/ agron_pubs/259. For information on how to cite this item, please visit http://lib.dr.iastate.edu/ howtocite.html. This Book Chapter is brought to you for free and open access by the Agronomy at Iowa State University Digital Repository. It has been accepted for inclusion in Agronomy Publications by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Corn Breeding Abstract Corn (Zea mays L.) breeding for hybrid development was begun in the early 1900s with the work of Shull (1909), East (1908), and others, but a primitive type of breeding was conducted for thousands of years by the American Indians before the European colonists began settlement in the New World. The .SU . Corn Belt dents were derived from crosses that included germ plasm of the northeastern flint and southern dent or gourdseed types, beginning about 1850, with subsequent selection that developed the U.S. Corn Belt dents. Open-pollinated cultivars, such as Reid Yellow Dent, Krug, Learning, and Lancaster Sure Crop were developed by a type of mass selection that was based on plant, ear, and grain type. This early work, which was done primarily by farmers and seedsmen, provided the germp1asm sources from which were developed the inbred parental lines that were used to produce the first double-cross hybrids used in the USA. Even to the present time, relatively little eg rm plasm from other countries has been used in corn breeding programs in the USA (Brown, 1975). Disciplines Agricultural Science | Agronomy and Crop Sciences | Plant Breeding and Genetics Comments This is a chapter from Haullauer, A. R., W. A. Russell, and K. R. Lamkey. 1988. Corn Breeding. In G. F. Sprague and J. W. Dudley (eds.) Corn and Corn Improvement. Agronomy 18:463-564. Am. Soc. of Agron., Madison, WI. Posted with permission. Rights Works produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The onc tent of this document is not copyrighted. This book chapter is available at Iowa State University Digital Repository: http://lib.dr.iastate.edu/agron_pubs/259 Published 1988 8 Corn Breeding l A. R. HALLAUER USDA-ARS Ames, Iowa WILBERT A. RUSSELL Iowa State University Ames, Iowa K.R.LAMKEY USDA-ARS Ames, Iowa Corn (Zea mays L.) breeding for hybrid development was begun in the early 1900s with the work of Shull (1909), East (1908), and others, but a primitive type of breeding was conducted for thousands of years by the American Indians before the European colonists began settlement in the New World. The U.S. Corn Belt dents were derived from crosses that included germ plasm of the northeastern flint and southern dent or gourd­ seed types, beginning about 1850, with subsequent selection that devel­ oped the U.S. Corn Belt dents. Open-pollinated cultivars, such as Reid Yellow Dent, Krug, Learning, and Lancaster Sure Crop were developed by a type of mass selection that was based on plant, ear, and grain type. This early work, which was done primarily by farmers and seedsmen, provided the germp1asm sources from which were developed the inbred parental lines that were used to produce the first double-cross hybrids used in the USA. Even to the present time, relatively little germ plasm from other countries has been used in corn breeding programs in the USA (Brown, 1975). Breeding procedures were used to improve and develop new strains of the open-pollinated cultivars in the late 1800s and early 1900s before the development of inbred lines for hybrid seed production was begun. These breeding procedures included varietal hybridization, mass selec­ tion, and ear-to-row selection. Descriptions of the procedures have been published in earlier years, and results from a few studies were summarized by Sprague and Eberhart (1977). These procedures were not successful to effect yield improvements. In some instances, varietal hybridization IJoint contribution of the USDA-ARS, and Journal Paper no. J-12562 of the Iowa Agric. and Home Econ. Exp. Stn., Ames, IA 5001 I. Project no. 2778. Copyright 1988 © ASA-CSSA-SSSA, 677 South Segoe Road, Madison, WI 537II, USA. Corn and Corn Improvement-Agronomy Monograph no. 18, 3rd edition. 463 464 HALLAUER ET AL. gave crosses that produced better than the higher-yielding parent, but the procedure was not accepted widely for commercial use. Selection pro­ grams were successful in producing numerous strains that varied for ma­ turity, plant type, ear and grain type, and pest resistance. Corn shows conducted at the start of the 20th century also caused selection for a distinct ear and grain appearance. Close selection to type, however, may have caused some inbreeding, which may have been the primary reason that yield improvements were not realized. Mass selection and ear-to­ row selection were gradually discontinued as inbred development for hybrid use became the accepted method. Modifications to mass selection (Gardner, 1961) and ear-to-row selection (Lonnquist, 1964) have been used to enhance the effectiveness of these selection methods for improv­ ing yield in breeding populations. Results of breeding studies by Shull, East, and Jones in the early 1900s led to the establishment of programs at many U.S. agricultural experiment stations and by the USDA fQr the development and evalu­ ation of inbred lines and hybrids during the period of 1915 to 1925. Corn breeding as a private commercial enterprise came a few years later. It was the 1930s before farmer use of hybrid seed became an acceptable practice; hybrid corn occupied approximately 100% of the corn area in Iowa by 1943, 90% of the corn area in the U.S. Corn Belt, but only 60% of the corn area for the entire USA (Fig. 8-1). Double-cross hybrids were the predominant type in the USA until about 1960 when the use of single crosses began to increase. Single crosses became the predominant type in a few years, with considerably fewer hectares being planted to related­ line single crosses, three-way crosses, and double crosses. Corn breeding for the development of inbred lines and hybrids in other parts of the world expanded rapidly after World War II. Corn has proved to be a flexible species amenable to selection such that progress 100 _-0 Iowa Corn Belt _--- "" /' _-0--- 90 'i' 0_--0--- USA , / '& 80 , / Z 70 , I 0 i= 60 / / a. g 50 cC J'/ I 11..40 0 , I w 30 , " l- cC ,/ a: 20 , I / I 10 ,/;)1 30 35 40 45 50 55 60 YEARS 1930-1960 Fig. 8-1. Rate of acceptance of double-cross hybrids in Iowa, the U.S. Corn Belt, and the USA. CORN BREEDING 465 has been achieved to develop types adapted to many areas where it was not grown or was relatively unimportant in earlier years. An excellent example has been the tremendous expansion in some European countries, made possible by the selection of earlier maturity, better adapted cultivars that can be grown successfully in areas where such was not feasible 40 years ago (Trifunovic, 1978). Some inbred development and evaluation were done in a few European countries before 1940, and such programs were expanded greatly after 1945. In the first period of this expansion, materials from the USA were evaluated and some U.S. hybrids were used. Subsequently, European and U.S. lines in hybrid combinations were de­ veloped and these helped to expand the corn-growing area and to give higher yields. The European lines introduced greater cold tolerance and adaptation for earlier maturity and the U.S. lines added improved yield and standability. These combinations permitted the expansion of hybrid corn into central Europe. In France, for example, the hectarage has in­ creased more than five times from pre-World War II to the present time, and France is now a leading corn producer in Europe. Corn has become the most important feed crop in southern and central Europe. Corn ranks second to wheat in total production among the world's cereal crops (CIMMYT, 1984). World corn production now normally exceeds 400 million t. During the period 1970-72 to 1981-83, world corn production increased about 120 million t, which represents a 42% increase in the world supplies at a rate of 3.1 % yc I. More than 50% of the total world area planted with corn is in Latin America, Africa, and south and southwest Asia, but probably <25% of the total grain production is in this area (Wellhausen, 1978). Hybrids are the primary type grown in Argentina, South Africa, and parts of Brazil, but the remainder of the area uses open-pollinated cuitivars, improved synthetics, variety crosses, and hybrids. In some areas where corn grain is used primarily for human consumption, considerable work has been done to improve protein qual­ ity through the use of opaque-2. As the technology is improved, it seems likely that hybrid types will become more important in most of the trop­ ical and subtropical areas. Corn grain yields in the USA have increased from approximately 1.3 Mg ha- I in 1930 to 7.5 Mg ha- l in 1985 (Fig.