2.3 Centers of Diversity for Common Crops
2.4 Global Movement of Food Crops
2.5 Considerations for the Future
2_The-Origin-Evolution-and-Diversity-of-Horticulture-Crops
Biodiversity Intl. & CIAT: Agrobiodiversity
CIAT: Where Our Food Comes From
https://www.smithsonianmag.com/history/the-great-british-tea-heist-9866709/
Rabobank: World Fruit Map
TeachEthnobotany: Crop Diversity & Global Food Systems with Dr. Colin Khoury
The Origin, Evolution, and Diversity of Horticulture Crops
Overview
Title Image: "Origins...” by Khoury, C.K. et al. from the International Center for Tropical Agriculture (CIAT) is licensed under CC BY 4.0
Did you have an idea for improving this content? We’d love your input.
Introduction
Lesson Objectives
Demonstrate understanding of origin, evolution, and diversity of plant life.
Match major crops with original regions of domestication.
Match major crops with wild progenitors.
Key Terms
field crops - plants grown commercially in large areas
forage crops - plants grown specifically to be grazed by livestock or conserved as hay
fruit crops - plants grown to produce sweet and fleshy, seed-bearing food
vegetable crops - plants grown with parts that are to be consumed by humans or other animals as food
Introduction
The crops that are most familiar to us today, as gardeners, farmers, and grocery store shoppers, were each domesticated in different areas of the planet. Many crops were primarily spread by human movement, while other crops were independently domesticated in more than one place. The area that a crop is believed to have originated is known as its “center of origin” (also known as its “center of diversity”).
It is important to learn the origins of agriculture across the globe, as well as identify regions of diversity for important crops in order to promote the equitable sharing of resources derived from collected plants; to ensure the conservation of germplasm of wild relatives, ancestors, and landraces of these crops; and to promote agricultural diversity and the wider use of genetically diverse and environmentally resilient crops.
Identifying Centers of Diversity
Excerpt adapted from "Origins of food crops connect countries worldwide" by Khoury, C.K. et al., Proceedings of the Royal Society of the Biological Sciences is licensed under CC BY 4.0
Over a century ago, advances in botany, linguistics, phytogeography and genetics made it possible to begin identifying the geographical origins of food crops (de Candolle, 1908). Building on this work, and informed by extensive travels over five continents, the Russian scientist N. I. Vavilov (Figure 9.2.1) proposed a number of independent ‘centers of origin’ of cultivated food plants around the world. These ‘centers of origin’ were places where he saw a diversity of traditional varieties for a wide range of crops, growing alongside their wild relatives. These reported centers of origin included Central America and Mexico; parts of the Andes, Chile and Brazil–Paraguay; the Mediterranean; the Near East; Ethiopia; Central Asia; India; China; and Indo-Malaysia (Figure 9.2.2) (Valivov, 1926, 1951, 1992).
Vavilov's interest in the centers of origin of crops was practical, as these regions were postulated to hold tremendous genetic variation that could be useful to the improvement of agriculture. Such variation was the product of adaptation of plants over relatively long periods of time to diverse environments and cultural practices. In these regions, for example, he hoped to find early-maturing varieties suitable for northern latitudes, and disease-resistant forms providing a solution to the mass starvation caused by cyclical failures of the wheat crop (Pringle, 2011). Since Vavilov, the regions of origin and diversity of different crops have been debated, investigated and refined, benefiting from an expanding body of archaeological, linguistic, genetic and taxonomic information (Harlan, 1951, 1971, 1975; Zhukovsky, 1965, 1968; Sinskaya, 1969; Zeven & Shukovsky, 1975; Zeven & de Wet, 1982; Hawkes, 1983; Price & Bar-Yosef, 2011).
‘Centers of diversity’ came to be preferred over ‘centers of origin’, to account for the understanding that high concentrations of crop varieties and related wild species are not located precisely where crops were initially domesticated in every case (Zeven & de Wet, 1982). Crop radiation from primary centers of diversity has also been more extensively documented, including identification of ‘secondary centers of diversity’ and other designations for more recent diversification patterns of some crops—e.g. Phaseolus bean in Southwestern Europe (Santalla et al., 2002), as well as barley (Tolbert et al., 1979) and oat (Diederichsen, 2008) in North America.
Centers of Diversity for Common Crops
We will explore the centers of diversity for a handful of common vegetable, fruit, field, and forage crops that the readers may be familiar with. Researchers have yet to come to a consensus as to the exact number and location of agricultural centers of origin. As previously noted, eight original Vavilvovian centers of origin included Central America and Mexico; parts of the Andes, Chile and Brazil–Paraguay; the Mediterranean; the Near East; Ethiopia; Central Asia; India; China; and Indo-Malaysia, although centers of diversity for individual crops may not conform to this theory.
This section will detail a selection of common crops native to each continent or otherwise defined regions on the globe. The information presented here is selected from The Seed Garden: The Art and Practice of Seed Saving, the International Center for Tropical Agriculture’s map of Origins and Primary Regions of Diversity of Agricultural Crops (Figure 9.2.3), and the University of Purdue’s website for their History of Horticulture course. This list, while not comprehensive, is intended to introduce students to the native regions of a few familiar crops.
North America
Vegetables
- Sunchoke, Helianthus tuberosus
Fruit and Nut Crops
- Blueberries and cranberries, Vaccinium spp.
- Chestnut, Castanea dentata
- Grapes, Vitis spp.
- Hazelnut, Corylus americana
- Persimmon, Diospyros virginiana
- Raspberries, Rubus spp.
- Strawberry, Fragaria virginiana
- Walnut, Juglans nigra
Field Crops (Cereals and Legumes)
- Tepary bean, Phaseolus acutifolius
Miscellaneous
- Sunflower, Helianthus annuus
Central America and Mexico
Vegetables
- Peppers, Capsicum spp.
- Sweet potato, Ipomoea batatas
Fruit and Nut Crops
- Avocado, Persea americana
- Cashew, Anacardium occidentale
- Papaya, Carica papaya
- Pumpkin, Cucurbita moschata
- Squash, Cucurbita pepo
Field Crops (Cereals and Legumes)
- Amaranth, Amaranthus cruentus, A. hypochondriacus
- Common bean, Phaseolus vulgaris
- Lima bean, Phaseolus lunatus
- Runner bean, Phaseolus coccineus
- Maize, Zea mays
Oil and Fiber Plants
- Bourbon cotton, Gossypium purpurascens
- Upland cotton, Gossypium hirsutum
Miscellaneous
- Cocoa, Theobroma cacao
- Vanilla, Vanilla spp.
South America
Vegetables
- Cassava, Manihot utilissima
- Peppers, Capsicum spp.
- Peanut, Arachis hypogaea
- Potato, Solanum tuberosum
- Tomato, Solanum lycopersicum
Fruit and Nut Crops
- Papaya, Carica spp.
- Pineapple, Ananas comosus
- Pumpkin, Cucurbita maxima, C. moschata
- Strawberry, Fragaria chiloensis
Field Crops (Cereals and Legumes)
- Adzuki bean, Vigna angularis
- Amaranth, Amaranthus caudatus
- Common bean, Phaseolus vulgaris
- Lima bean, Phaseolus lunatus
- Quinoa, Chenopodium quinoa
Oil and Fiber Plants
- Egyptian cotton, Gossypium barbadense
Miscellaneous
- Mate, Ilex paraguariensis
Africa
Vegetables
- Okra, Abelmoschus esculentus
- Yam, Dioscorea rotundata
Fruit and Nut Crops
- Olive, Olea europaea
- Melons, Cucumis melo
- Watermelon, Citrullus lanatus
Field Crops (Cereals and Legumes)
- African millet, Eleusine coracana
- Cowpea, Vigna unguiculata
- Pearl millet, Pennisetum spicatum
- Sorghum, Sorghum bicolor
Oil and Fiber Plants
- Castor bean, Ricinus communis
- Sesame, Sesamum indicum
Miscellaneous
- Coffee, Coffea arabica
Europe
Vegetables
- Asparagus, Asparagus officinalis
- Cabbage, Brassica oleracea
- Turnip, Brassica rapa
Fruit and Nut Crops
- Cherries and plums, Prunus spp.
- Chestnut, Castanea sativa
- Currants, Ribes spp.
- Hazelnut, Corylus avellana
- Raspberries, Rubus idaeus
- Walnut, Juglans regia
Field Crops (Cereals and Legumes)
- Oats, Avena spp.
Forage Crops
- Clover, Trifolium spp.
Oil and Fiber Plants
- Flax, Linum usitatissium
- Olive, Olea europaea
- Rape, Brassica napus
Middle East and the Mediterranean Region
Vegetables
- Artichoke, Cynara cardunculus
- Asparagus, Asparagus officinalis
- Beet, Beta vulgaris
- Cabbage, Brassica oleracea
- Celery, Apium graveolens
- Leeks, Allium ampeloprasum
- Lettuce, Lactuca sativa
- Onion, Allium cepa
- Spinach, Spinacia oleracea
- Turnip, Brassica rapa
Fruit and Nut Crops
- Cherries and plums, Prunus spp.
- Date, Phoenix dactylifera
- Fig, Ficus carica
- Grape, Vitis vinifera
- Pears, Pyrus communis
- Quince, Cydonia oblonga
Field Crops (Cereals and Legumes)
- Barley, Hordeum vulgare
- Chickpea, Cicer arietinum
- Fava bean, Vicia faba
- Lentil, Lens culinaris
- Oats, Avena spp.
- Pea, Pisum sativum
- Rye, Secale cereale
- Sesame, Sesamum spp.
- Wheat, Triticum spp.
Forage Plants
- Alfalfa, Medicago sativa
- Clover, Trifolium spp.
- Vetch, Vicia spp.
Oil and Fiber Plants
- Black mustard, Brassica nigra
- Flax, Linum usitatissimum
- Olive, Olea europaea
- Rape, Brassica napus
Asia (excluding the Middle East)
Vegetables
- Asparagus, Asparagus officinalis
- Cabbage, Brassica rapa
- Carrot, Daucus carota
- Celery, Apium graveolens
- Cucumber, Cucumis sativus
- Eggplant, Solanum melongena
- Okra, Abelmoschus esculentus
- Yam, Dioscorea alata
Fruit and Nut Crops
- Almond, Amygdalus communis
- Apple, Malus pumila
- Apricots, cherries, peaches, nectarines, and plums, Prunus spp.
- Bananas, Musa spp.
- Chestnut, Castanea mollissima
- Citrus fruits, Citrus spp.
- Kiwi, Actinidia deliciosa
- Mango, Mangifera indica
- Melons, Cucumis melo
- Pear, Pyrus asiatica
- Persimmon, Diospyros kaki
- Raspberries, Rubus crataegifolius
- Walnut, Juglans regia
Field Crops (Cereals and Legumes)
- Buckwheat, Fagopyrum esculentum
- Millet, Panicum spp.
- Rice, Oryza sativa
- Sorghum, Sorghum bicolor
- Soybean, Glycine max
Forage Crops
- Clover, Trifolium spp.
Oil and Fiber Plants
- Coconut, Cocos nucifera
- Cotton, Gossypium herbaceum
- Hemp, Cannabis indica
- Flax, Linum usitatissium
- Olive, Olea europaea
- Oriental cotton, Gossypium nanking
- Sesame, Sesamum indicum
- Tree cotton, Gossypium arboreum
Miscellaneous
- Cinnamon, Cinnamomum spp.
- Sugarcane, Saccharum officinarum
- Tea, Camellia sinensis
Australia and the Pacific Region
Vegetables
- Taro, Colocasia esculenta
Fruit and Nut Crops
- Coconut, Cocos nucifera
- Macadamia nut, Macadamia integrifolia
Global Movement of Food Crops
Excerpt adapted from "Origins of food crops connect countries worldwide" by Khoury, C.K. et al., Proceedings of the Royal Society of the Biological Sciences is licensed under CC BY 4.0
The geographical isolation that contributed to the development of variation in cultivated food plants also largely restricted this diversity to its primary regions or nearby areas throughout most of recorded history, although notable long-distance migrations of some crops have been recognized—e.g. sorghum and millets between Africa and South Asia (Fuller et al., 2011) and maize in the Americas (Staller et al., 2006)). The exchange of food crops, diseases, ideas, and populations between the New World and the Old World following the voyage to the Americas by Christopher Columbus in 1492 is referred to as the Columbian Exchange (Nunn & Quian, 2010). According to Charles Mann in his work 1493, “To ecologists, the Columbian Exchange is arguably the most important event since the death of the dinosaurs.”
The ‘age of discovery’ and in particular the Columbian Exchange marked key accelerations in the movement of food plants, as they were introduced to colonizing countries and to new regions with growing colonial establishments and emerging export-oriented production (McKinney, 1999; Diamond, 2004; Romão, 2000). The movement of food crops during the Columbian exchange happened quite quickly for many of these plants. Potatoes, for example, were first seen by European explorers in 1551 and were already being cultivated in the Canary Islands by 1567 (Domingo et al., 2007). Cultivation in new agricultural areas was in many cases remarkably successful, in part owing to escape from crop-specific pests and pathogens (Jennings & Cock, 1977). Complementarity in terms of production season or dietary needs also facilitated some crops' rapid acceptance—e.g. maize in Italy (Nabhan, 1993).
The expansion of human settlement, driven by ever more efficient transportation and increases in global trade, have decoupled the consumption of crops from their production (Fader et al., 2013). Bananas, a crop requiring tropical growing conditions, are now consumed in at least 167 countries, including all temperate regions (FAO, 2015). Ongoing economic and agricultural development, as well as globalization trends, have made a greater variety of major food commodities available to consumers in countries worldwide, but in turn increased homogeneity in the global food system (Khoury et al., 2014; Kearney, 2010); these developments and trends include increasing consumer purchasing power in developing regions, the rise of supermarkets and convenience foods, greater consumption outside the home, urbanization, refrigerated transport, agricultural subsidies, industrial food technologies, and facilitated trade agreements. Given this homogenization in global food supplies, the geographical decoupling of agricultural production and food consumption (Fader et al., 2013; Porkka et al., 2013; D’Ordorico et al., 2014; MacDonald et al., 2015), as well as greater consumption of packaged and processed food products (Kearney, 2010), it is increasingly feasible to imagine not only mistakenly attributing the origin of potatoes to Ireland, tomatoes to Italy (Figure 9.2.4), and chilli peppers to Thailand, but also losing the connection of crops with a geographical origin entirely.
Considerations For the Future
Equitable Sharing of Resources
The search for useful plants is as old as horticulture itself. However, professional plant hunting reached its height in the 1800s, when rapid advances in transportation and the development of the Wardian case (a special terrarium designed for moving plants over long sea voyages) led to an explosion in plant collecting. Plant hunters were usually hired by European and North American government agencies or wealthy aristocrats to collect new species from other countries.
While some plant collectors operated with permission from the host country, others who did not have consent would illegally enter out-of-bound areas and steal plants. One famous example of botanical theft is the story of how tea (Camellia sinensis) seeds, along with other secrets of the tea trade, were smuggled out of China. In 1848, England’s East India Company hired Robert Fortune to sneak into China’s interior in disguise to steal plants and information, which would later be used to establish tea plantations in India—an English colony at that time. The East India Company went on to dominate the tea trade, amassing funds that would otherwise have gone to Chinese tea growers (Rose, 2010).
In 1992, the United Nations Environment Programme’s Earth Summit in Rio de Janeiro, Brazil set in place the Convention on Biological Diversity. The objectives are
the conservation of biological diversity, the sustainable use of its components and the fair and equitable sharing of the benefits arising out of the utilization of genetic resources, including appropriate access to genetic resources and appropriate transfer of relevant technologies, taking into account all rights over those resources and to technologies, and appropriate funding.
Thanks to the Convention on Biological Diversity, plant germplasm is now considered a country’s natural resource. Plant collectors may only work with prior governmental permission under specific collection permits, with specific material transfer agreements that outline how benefits will be shared if germplasm is commercialized (McMahon, 2020).
Germplasm Conservation
The genes of ancestors, wild relatives, and landrace varieties of modern crops are vital for breeding efforts that will allow humans to produce enough food to support rapidly growing populations. The genetic material (or “germplasm”) of these plants can be used to introduce pest and disease resistance, environmental adaptability, and increased productivity.
Many important species, including wild relatives and ancestors of modern crops, are threatened by habitat loss caused by human development. Landrace and heirloom varieties that are the product of millennia of careful plant selection are also at risk of being lost as more farmers give up traditional methods in favor of modern crops or quit farming altogether. There are many organizations dedicated to protecting germplasm by collecting seed to store ex situ in seed banks and botanic gardens and in situ by conserving native habitats of agriculturally important species.
Agricultural Biodiversity
Modern agriculture is based around monoculture plantings where a single crop is grown over large expanses. This practice allows for better uniformity in the planting, cultivation, and harvest of the crop. However, when the same species, variety, and sometimes genetically identical clones, are grown over large areas on an annual basis, they are often more susceptible to pest and disease pressures, meaning that crops will require more inputs or risk loss in yields.
The world relies on just three crops—rice, wheat and maize—for more than 50% of its plant-derived calories, and yield of these crops has plateaued. While there is a need for breeding and improvement programs for these major crops, there are tens of thousands of alternative crops that have been used for human food since the origin of agriculture. These alternative crops, such as quinoa, amaranth, and millet, can complement and even substitute our modern staples.
Despite the environmental and nutritional need for these alternative crops, their cultivation is decreasing rather than increasing. The practice of agricultural biodiversity encourages the thoughtful use of alternative crops that better suit the environment where they are grown, in order to meet the nutritional needs of our growing population. The organization Biodiversity International defines agricultural biodiversity as:
the variety and variability of animals, plants and micro-organisms that are used directly or indirectly for food and agriculture, including crops, livestock, forestry and fisheries. It comprises the diversity of genetic resources (varieties, breeds) and species used for food, fodder, fiber, fuel and pharmaceuticals. It also includes the diversity of non-harvested species that support production (soil micro-organisms, predators, pollinators), and those in the wider environment that support agro-ecosystems (agricultural, pastoral, forest and aquatic) as well as the diversity of the agroecosystems.
The practice of agricultural biodiversity, in conjunction with continued breeding improvements of modern crops, is a more nuanced approach to agriculture that promotes adapting the crop to the environment rather than the other way around. Studying agricultural centers of origin and identifying centers of diversity for various crops will allow for better crop selection in the future.
Dig Deeper
For an interactive resource that aids exploring links between regional food systems and the primary regions of diversity, visit the International Center for Tropical Agriculture website.
To review a map highlighting the trade of fruit across the globe for the year 2016, check out the Rabobank website.
To learn more about “The Great British Tea Heist”, check out this article in the Smithsonian Magazine
For more information about agrobiodiversity, visit the Alliance Biodiversity website.
For an interview where Dr. Khouri shares how collaborative work brings together multidisciplinary expertise to inform conservation strategies for crops and their wild relatives, develop conservation indicators for international agreements, and support evidence-based decision making toward more sustainable food systems, watch the video below or follow this YouTube link.
Attribution and References
Attribution
Excerpts adapted from "Origins of food crops connect countries worldwide" by Khoury, C.K. et al., Proceedings of the Royal Society of the Biological Sciences is licensed under CC BY 4.0
Title Image: "Origins and primary regions of diversity of agricultural crops” by Khoury, C.K. et al. from the International Center for Tropical Agriculture (CIAT) is licensed under CC BY 4.0
References
Bioversity International (2017). Mainstreaming agrobiodiversity in sustainable food systems: Scientific foundations for an agrobiodiversity index. Rome (Italy): Bioversity International, 180 p. ISBN: 978-92-9255-070-7
Colley, M., Zystro, J., Buttala, L. A., & Siegel, S. (2015). The seed garden: The art and practice of seed saving. Seed Savers Exchange.
de Candolle, A. (1908). Origin of cultivated plants. New York, NY: D Appleton.
Diamond, J. (2004). The wealth of nations. Nature 429, 616–617.
Diamond, J. (2002). Evolution, consequences and future of plant and animal domestication. Nature (London), 418(6898), 700–707. https://doi.org/10.1038/nature01019
Diamond, J. (2005). Guns, germs, and steel: The fates of human societies. W.W. Norton.
Diederichsen, A. (2008). Assessments of genetic diversity within a world collection of cultivated hexaploid oat (Avena sativa L.) based on qualitative morphological characters. Genet. Resour. Crop Evol. 55, 419–440.
Domingo Ríos, D., Ghislain, M., Rodríguez, F. & Spooner, D.M. (2007). What is the origin of the European potato? Evidence from the Canary Island landraces. Crop Sci. 47, 1271–1280.
D'Odorico. P., Carr, J.A., Laio, F., Ridolfi, L. & Vandoni, S. (2014). Feeding humanity through global food trade. Earth's Future 2, 458–469.
Fader, M., Gerten, D., Krause, M., Lucht, W. & Cramer, W. (2013) Spatial decoupling of agricultural production and consumption: quantifying dependences of countries on food imports due to domestic land and water constraints. Environ. Res. Lett. 8, 014046.
FAO. (2015). FAOSTAT. Rome, Italy: Food and Agriculture Organization of the United Nations. See http://faostat3.fao.org/.
Fuller, D.Q., Boivin, N., Hoogervorst, T., Allaby, R. (2011). Across the Indian Ocean: the prehistoric movement of plants and animals. Antiquity 85, 544–558.
Harlan, J.R. (1951). Anatomy of gene centers. Am. Nat. 8, 97–103.
Harlan, J.R. (1971). Agricultural origins: centres and noncentres. Science 174, 468–474.
Harlan, J.R. (1975). Crops and man. Madison, WI: American Society of Agronomy and Crop Science Society of America.
Hawkes, J.G. (1983). The diversity of crop plants. Cambridge, MA: Harvard University Press.
Jennings, P.R. & Cock, J.H. (1977). Centres of Origin of crops and their productivity. Econ. Bot. 31, 51–54.
Kearney, J. (2010). Food consumption trends and drivers. Phil. Trans. R. Soc. B 365, 2793–2807.
Khoury, C.K., Bjorkman, A.D., Dempewolf, H., Ramirez-Villegas, J., Guarino, L., Jarvis, A., Rieseberg, L.H. & Struik, P.C. (2014). Increasing homogeneity in global food supplies and the implications for food security. Proc. Natl Acad. Sci. USA 111, 4001–4006.
Janick, J. (2008). Lecture 5: Centers of Origin of Crop Plants. Purdue University. Retrieved July 2021 from https://www.hort.purdue.edu/newcrop/Hort_306/text/lec05.pdf
MacDonald, G.K., Brauman, K.A., Sun, S., Carlson, K.M., Cassidy, E.S., Gerber, J.S. & West, P.C. (2015). Rethinking agricultural trade relationships in an era of globalization. Bioscience 65, 275–289.
McKinney, S. (1999). Bligh!: The whole story of the mutiny aboard HMS Bounty. Victoria, British Columbia: TouchWood Editions.
Mann, C.C. (2011). 1493: Uncovering the new world Columbus created (1st ed.). Alfred A. Knopf.
McMahon, M. (2020). Plant science: Growth, development, and utilization of cultivated plants (Sixth edition.). Pearson Education, Inc.
Nabhan, G. (1993). Songbirds, truffles, and wolves: an American naturalist in Italy. New York, NY: Penguin Books.
Nunn, N. & Qian, N. (2010). The Columbian Exchange: A history of disease, food, and ideas. Journal of Economic Perspectives 24(2), 163–188. Retrieved 22 February 2022 from https://scholar.harvard.edu/files/nunn/files/nunn_qian_jep_2010.pdf
Porkka, M., Kummu, M., Siebert, S. & Varis, O. (2013). From food insufficiency towards trade dependency: a historical analysis of global food availability. PLoS ONE 8, e82714.
Price, T.D. & Bar-Yosef, O. (2011). The origins of agriculture: new data, new ideas. An introduction to supplement 4. Curr. Anthropol. 52, S163–S174.
Pringle, P. (2011). The murder of Nikolai Vavilov: the story of Stalin‘s persecution of one of the great scientists of the twentieth century. New York, NY: Simon & Schuster.
Raven, P.H., R.F. Evert, and S.E. Eichhorn. (2005). Plants and People. Biology of plants. 7th ed (pp. 475-495). W.H. Freeman and Company, Worth Publishers, New York.
Romão, R.L. (2000). Northeast Brazil: a secondary center of diversity for watermelon (Citrullus lanatus). Gen. Res. Crop Evol. 47, 207–213.
Rose, S. (2010). The great British tea heist. Smithsonian Magazine. Retrieved 21 February 2022 from https://www.smithsonianmag.com/history/the-great-british-tea-heist-9866709/
Santalla, M., Rodino, P & De Ron, M. (2002). Allozyme evidence supporting southwestern Europe as a secondary centre of genetic diversity for the common bean. Theor. Appl. Genet. 104, 934–944.
Sinskaya, E.N. (1969). Historical geography of cultivated floras (at the dawn of agriculture). Leningrad, USSR: Kolos.
Staller, J., Tykot, R. & Benz, B. (2006). Histories of maize: multidisciplinary approaches to the prehistory, linguistics, biogeography, domestication, and evolution of maize. Walnut Creek, CA: Left Coast Press.
Tolbert, D.M., Qualset, C.O., Jain, S.K., Craddock, J.C. (1979). A diversity analysis of a world collection of barley. Crop Sci. 19, 789–794.
Vavilov, N.I. (1926). Tzentry proiskhozhdeniya kulturnykh rastenii [The centres of origin of cultivated plants]. Works Appl. Bot. Plant Breed. 16, 1–248.
Vavilov, N.I. (1951). The origin, variation, immunity and breeding of cultivated plants (transl. K Start). Cron. Bot. 13, 1–366.
Vavilov NI. (1992). Origin and geography of cultivated plants (transl. D Löve). Cambridge, UK: Cambridge University Press.
Zeven, A.C. & Zhukovsky, P. (1975). Dictionary of cultivated plants and their centres of diversity: excluding most ornamentals, forest trees and lower plants. Wageningen, The Netherlands: CAPD.
Zhukovsky, P.M. (1965). Main gene centres of cultivated plants and their wild relatives within the territory of the U.S.S.R. Euphytica 14, 177–188.
Zhukovsky, P.M. (1968). New centres of origin and new gene centres of cultivated plants including specifically endemic microcentres of species closely allied to cultivated species. Bot. J. (Russian Bot Z.) 53, 430–460.