Compared to the vast numbers of terrestrial plant species in nature, domesticated crops number few. Yet, humans will need new crops that will grow productively in abandoned or underutilized lands to meet the growing need for food, fuel, fiber, and chemicals.
Domestication is the process by which humans select for inheritance of desirable traits. During “traditional” domestication, crop species underwent intense selective pressures over centuries that altered their underlying genetic makeup, or genomes. Now that DNA differences between wild ancestors and a number of crop species have been determined, modern genomic science can be applied to accelerate domestication by directly selecting for gene sequences and genomic configurations in undomesticated plants of promise. (more on this topic in a future blog)
At TerViva we are domesticating one such promising plant, a legume tree with high oil seed content, pongamia. Pongamia seeds are a promising source of renewable oil for fuel and agricultural and industrial chemicals. For this blog posting, I would like to give a historical context for how humans domesticated two important food crops: corn an annual grain and almonds, a perennial orchard tree.
Around the world today, more corn is grown and harvested each year than any other grain. The 2012 corn harvest exceeded 800 million tons. US farmers alone produce 40% of the world’s corn harvest on 95 million acres. (Crop Production 2012 Annual Summary, U.S. Department of Agriculture’s National Agricultural Statistics Service). Other top corn producing countries include China, Brazil, Mexico, Indonesia, India, France and Argentina. (http://www.indexmundi.com/agriculture/?commodity=corn)
Harvested primarily for its seeds, corn is consumed directly by humans and livestock, processed for packaged foods, pressed to expel cooking oil, and further processed for industrial purposes including ethanol for biofuel. Sugar-rich varieties called sweet corn are usually grown for human consumption, while field corn varieties are used for animal feed and as chemical feedstocks.
The domestication of maize began some 9000 years ago and continues today. (http://en.wikipedia.org/wiki/Corn). Indigenous people in Mesoamerica first cultivated wild grasses in the genus of teosinte slowly selecting individuals in their cultivated fields that had more favorable properties. About 2500 BCE, maize began spreading through much of the Americas. Europeans brought this new world crop back to Europe after Columbus’ voyage of New World discovery in 1492. Because of its ability to grow in diverse climates maize spread to many areas throughout the world where it is grown today.
During its slow domestication journey, humans bred a new species (Zea maize) that produces larger ears with a greater number of seeds than its wild ancestor. In addition, corn seeds are free of the stony casings produced by teosinte and they remain attached to the cob in contrast to teosinte seeds whose ears shatter for seed dispersal upon maturation. Humans also selected for taller plants without branches but with multiple leaves.
Wild teosintes and maize, although considered distinct species, are still closely related, have similar chromosomes and are able to be crossed one to another to produce fertile hybrids. (New York Times, May 24, 2010). Early Americans were able to transform a grass with many inconvenient, unwanted features into a high-yielding, easily harvested food crop by painstaking trial and error because physical differences between wild teosintes and corn, result from only 4-5 genes.
Sophisticated modern corn breeding that has further transformed this crop into a high yielding commodity began in the 1860s in the United States where farmers selected plants with high yields in their fields and produced seed to sell to other farmers. University supported breeding programs played a pivotal role in further developing commercial varieties and introducing modern corn hybrids. (Hybrid Maize Breeding and Seed Production pub. 1958). By the 1930s, corn-breeding companies such as Pioneer had begun to influence long-term corn varieties.
The latest technological innovations being applied to corn and other major crops include genetic engineering to create transgenic or genetically modified (GMO) varieties of corn with specific traits such as glyphosate resistance (coupled with the herbicide glyphosate) to aid in weed management and genomics to mine and harness inherent genetic variation for further yield advances.
Today almonds are the world’s most widely cultivated nuts. In 2011, global production exceeded 900,000 million metric tons. The US (California) produces 80% of the world’s almonds followed by Spain, Australia, and Turkey. In California almonds are cultivated on more than 800,000 acres, most of which are actively managed and include irrigation. (Business Week citing The Associated Press, January 21, 2011)
One of the first domesticated nut trees, almonds show up in archeological sites of the Mediterranean dating to the Bronze Age, 3000-2000 BCE. Seedlings were planted on hillsides in regular arrays or orchards to escape frost. Wild almond species were already adapted to marginal soils and cultivated orchards were not irrigated.
Early colonists brought almonds to the US including the earliest successful orchard in California in the foothills of the Sacramento valley in 1843, again without irrigation.
Wild almonds plants are difficult to propagate from suckers or from cuttings, but early
growers were able to produce healthy orchards by planting seedlings from seeds. Thus, almonds were domesticated even before the introduction of grafting. In use before 2000 BCE. in China and spreading throughout Asia and Europe, grafting is an ancient horticultural technique still widely used today, whereby tissues from one plant are inserted into those of another and vascular tissues from the two different plants join together and the roots of one genetic type support the growth of branches, flowering and seed production of another genetic type.
Using grafted trees, genetic selection proceeded along two independent tracks for roots vs. above ground plant traits. Almond rootstocks have been selected for beneficial root properties (resistance to nematodes, salinity tolerance, etc.) while above ground plant material or scion donors have been selected for nut yield and consumer preferences of texture and taste.
Wild almonds taste bitter. Wild almond kernels produce cyanide when handled as during harvesting. Eating even a few dozen wild almond seeds at one sitting can be fatal. Selection of the sweet type, from the many bitter types in the wild, marked the beginning of almond domestication.
Early growers in California failed to understand the need for cross-pollination via bees. An early California grower (AT Hatch) selected 4 varieties for grafting in 1879 and deployed all 4 in orchards to enable cross pollination). Other early California growers experimented further with new varieties and by 1925, the USDA listed more than 150 varieties in production in a technical bulletin (Technical Bulletin 1282). As with corn, academic research has played and continues to play a key role in almond variety development. The University of California provided much of the early research and evaluation of almond varieties. In recent years, USDA ARS scientists have developed a self pollenating variety of almonds (http://www.ars.usda.gov/is/AR/archive/apr10/ almonds0410.pdf) that may alleviate the biological necessity (and associated costs) for bees to cross pollenate almond orchards. Domesticated varieties of almonds like domesticated corn are still very close genetically to wild varieties.
Genomic science is being applied to all major existing crops to improve growth and yield characteristics of already domesticated plants. These new technologies should help us shorten the domestication of pongamia from centuries to decades.
Claire Kinlaw, PhD, MBA leads product development for TerViva, bridging plant science to what customers need for crop products. She has over 20 years experience leading plant genomics research projects and before joining TerViva she consulted in the fields of economic development and organizational development.