Maize genetic resources
Contact person for Maize: Denise Costich, CIMMYT, Mexico
Contributors to this page: CIMMYT, Mexico (Suketoshi Taba, Bonnie J. Furman), with inputs also received from IITA, Nigeria (Dominique Dumet); EMBRAPA (maize and sorghum genebank), Brazil (Flavia Teixeira); USDA (ARS/NC7, ISU), USA (Mark Millard).
External reviewer: Major Goodman (NC State University, USA).
Compilation of best practices
Information on current practices for genebank management of maize was provided by partners from CIMMYT, IITA, and major maize genebanks including the USDA/ARS/NC7 (ISU, USA) and EMBRAPA maize and sorghum genebank (Brazil), as well as reviewed from literature and existing websites (e.g. the Maize Knowledge Bank). This provided the basic information for selection, justification and recommendations for best practices of maize conservation, complemented with relevant photos and revised and validated by crop experts.
It is our wish that this knowledge base for ex situ management of maize genetic resources assists maize germplasm curators to better manage their collections. The knowledge base will be improved and updated regularly to make maize germplasm more accessible to breeders and farmers for the development of useful breeding lines, varieties and hybrids.
Importance and origin
Maize is one of the world’s three most important cereals along with wheat and rice. Maize is currently produced on nearly 100 million hectares in 125 developing countries and is among the three most widely grown crops in 75 of those countries (FAOSTAT, 2010). Although much of the world’s maize production (approximately 78%) is utilized for animal feed, human consumption in many developing and developed countries is steadily increasing. For example, maize is the most important cereal crop for food in sub-Saharan Africa and Latin America. The growing demand for food consumption in developing countries alone is predicted to increase by around 1.3% per annum until 2020 (Ortiz et al. 2010). Between now and 2050, the demand for maize in the developing world will double, and by 2025, maize is likely to become the crop with the greatest production globally (Rosegrant et al. 2010).
The maize plant has characteristics of wide adaptability in the different ranges of growing conditions. Thus, it has gained adaptation and productivity in all continents through introductions and breeding. The genetic diversity of maize, being an outcrossing crop, is very broad for conservation and utilization in breeding programmes. Maize landraces exhibit significant morphological variation and genetic polymorphism and are grown from sea level to 3800 m. (Ortiz et al. 2010).
Maize is believed to have been domesticated from teosinte (Z. mays ssp. parviglumis Iltis & Doebley) in southern Mexico more than 6000 years ago (Matsuoka et al. 2002). Recent archeological evidence suggests that maize was present in the central Balsas near Iguala Valley in Guerrero state, Mexico in 8700 B.C. (Piperno et al. 2009). Further maize evolution and its expansion into other regions of Mexico and in Central America (Mesoamerica) followed (Piperno and Flannery, 2001; Webster et al. 2005), subsequently spreading from Mesoamerica to other parts of the world over several thousands of years.
The major types of cultivated maize (Zea mays L.) under conservation are characterized by their kernel types: dent, flint, floury, sugary, pop and morocho (a soft floury texture inside the grain, surrounded by a hard flint texture). Grain colours are white, yellow, purple, orange yellow, red, sun red, blue, mottled and brown.
There are 300 or more Latin American maize race names and local names in the CIMMYT maize collection (Taba, 2003).
Cultivated maize has two close relatives Tripsacum spp. and teosinte. Although Tripsacum spp. is morphologically very different, it is genetically related to maize. Tripsacum diversity is found extensively in Mexico and Guatemala as well as other countries in the Americas (Taba et al. 2004a; Wilkes 2004). Teosinte is a wild relative and the closest relative of maize. Mexico, Guatemala and Nicaragua are the countries where teosinte races grow in situ.
Maize is mainly used for animal feed in developed country economies, but it is the main staple food in many developing countries. Dry-milling industries produce grits, meal and flour. The wet-milling industry produces corn starch, oil and syrups. Maize is often a component of numerous types of food (breads, cakes, biscuits, soups, sauces, porridges, cereals and popcorn). Maize products of the fermentation and distilling industry include alcohols and whisky. The whole plant is also widely used for silage.
Production and research
Research on maize genetics and breeding, from the early part of the twentieth century, significantly has increased grain yield in USA and other temperate maize growing countries, and supports the same trend in subtropical and tropical maize growing regions. Global maize production is estimated to be over 800 million tons per year (FAO, 2010), and is expected to increase in years ahead.
Maize research has advanced from landraces to varieties, to maize hybrids: double cross, three-way cross and single cross, and recently transgenic maize hybrids. The optimized use of adapted and exotic germplasm in various production environments is a key to the continued success in increasing grain yield and other trait-specific products: green ear, forage, oil, protein, starch, etc. Stress tolerant hybrids and varieties are bred with genetic diversity, accumulated and available from breeder gene pools. Ex situ maize genebanks have a role in supporting the production of breeder gene pools with unique genetic diversity. For example, new enhanced maize germplasm is being created using genebank accessions in Germplasm Enhancement of Maize (GEM), USA (Pollak, 2003).
References and further reading
Brandolini A. 1970. Maize. In: Frankel OH, Bennett E, editors. Genetic Resources in Plants: Their Exploration and Conservation. F.A. Davis Co., Philadelphia. pp. 273-309.
Dunn ME. 1975. Ceramic evidence for the prehistoric distribution of maize in Mexico. American Antiquity, Vol. 40, 3:305-314 Published by: Society for American Archaeology.
Goodman MM, Brown WL. 1988. Races of corn. In: Sprague GF, Dudley JW, editors. Corn and corn improvement, third edition, monograph 18. American Society of Agronomy, Inc., Crop Science Society of America, Inc. and Soil Science Society of America, Inc. pp. 33-79.
FAOSTAT [homepage] [online] Food and Agriculture Organization of the United Nations. Available from: http://faostat.fao.org/site/567/default.aspx. Date accessed: April 2010.
Matsuoka Y, Vigouroux Y, Goodman MM, Sanchez-G J, Buckler E, Doebley J. 2002. A single domestication for maize shown by multilocus microsatellite genotyping. Proceedings of the National Academy of Sciences. (PNAS) USA. 99:6080-6084. Available from: teosinte.wisc.edu/pdfs/Matsuoka_et_al_PNAS.pdf . Date accessed: 3 September 2010.
Ortiz R, Taba S, Chávez Tovar VH, Mezzalama M, Xu Y, Yan J, Crouch, JH. 2010. Conserving and Enhancing Maize Genetic Resources as Global Public Goods– A Perspective from CIMMYT. Crop Science 50:13–28.
Piperno DR, Flannery KV. 2001. The earliest archaeological maize (Zea mays L.) from Highland Mexico: New accelerator mass spectrometry dates and their implications. Proceedings of the National Academy of Sciences. (PNAS) USA. 98:2101-2103. Available from: www.pnas.org/content/98/4/2101.full.pdf+html. Date accessed: 3 September 2010.
Piperno DR, Ranere AJ, Hoist I, Dickau R, Iriarte J. 2009. Starch grain and phytolith evidence for early ninth millennium B.p. maize from the Central Balsas River Valley, Mexico. Proceedings of the National Academy of Sciences. (PNAS) USA. 106: 5019-5024. Available from: www.pnas.org/content/early/2009/03/20/0812525106.full.pdf+html. Date accessed: 3 September 2010.
Pollak LM. 2003. The history and success of the public-private project on germplasm enhancement of maize (GEM). Advances in Agronomy. 78:45-87. Available from: http://www.public.iastate.edu/~usda-gem/Publications/Publications/Advances%20in%20Agronomy.pdf. Date accessed: 3 September 2010.
Rosegrant MW, Msangi S, Ringler C, Sulser TB, Zhu T, Cline SA. 2008. International Model for Policy Analysis of Agricultural Commodities and Trade (IMPACT): Model Description. International Food Policy Research Institute: Washington, D.C. Available from: www.ifpri.org/themes/impact/impactwater.pdf. Date accessed: 3 September 2010.
Taba S, van Ginkel M, Hoisington D, Poland D. 2004a. Wellhausen-Anderson Plant Genetic Resources Center: Operations Manual, 2004. El Batan, Mexico: CIMMYT. Available here.
Taba S, Eberhart SA, Pollak LM. 2004b. Germplasm resources. In: Smith CW, Betran J, Runge ECA, editors. Corn: origin, Technology, and Production. John Wiley & Sons, Inc. pp 99-132.
Taba S. 2003. Preliminary breeder core subsets and prebreeding in Latin American maize germplasm conservation: regeneration, in-situ conservation, core subsets, and prebreeding: proceedings of a workshop held at CIMMYT. April 7-10, 2003. Mexico, D.F.: CIMMYT. pp. 9-25. Click here to download this publication.
Taba S. 1997. Maize. In: Fuccillo D, Sears L, Stapleton P, editors. Biodiversity in Trust, conservation and use of plant genetic resources in CGIAR Centers. Cambridge Univ. Press. pp. 213-226.
Webster D, Rue D, Traverse A. 2005. Early Zea cultivation in Honduras: Implications for the Iltis hypothesis. Economic Botany 59, 2:101-111. Available from: www.anthro.psu.edu/faculty_staff/docs/Webster_EconomicBotany.pdf or http://www.jstor.org/discover/10.2307/4256956?uid=3738296&uid=2&uid=4&sid=21101838211523 Date accessed: 2 April 2013.
Wellhausen EJ, Roberts LM, Hernandez-Xolocotzi E, in collaboration with Mangelsdorf PC. 1952. Races of maize in Mexico. Bussey Institution, Harvard University, Cambridge, MA.
Wilkes G. 2004. Corn, strange and marvelous: but is a definitive origin known? In: Smith CW, Betran J, Runge ECA, editors. Corn: origin, Technology, and Production. John Wiley & Sons, Inc. pp. 3-64.