The oat (Avena sativa), sometimes called the common oat, is a species of cereal grass (Avena) grown for fodder and for its seed, which is known by the same name (usually in the plural). Oats appear to have been domesticated as a secondary crop, as their seeds resembled those of other cereals closely enough for them to be included by early cultivators. Oats tolerate cold winters less well than cereals such as wheat, barley, and rye, but need less summer heat and more rain, making them important in areas such as Northwest Europe that have cool, wet summers. They can tolerate low-nutrient and acid soils. Oats grow thickly and vigorously, allowing them to outcompete many weeds, and compared to other cereals are relatively free from diseases. Oats are used for human consumption as oatmeal, including as steel cut oats or rolled oats. Global production is dominated by Canada and Russia; global trade is a small part of production, most of the grain being consumed within the producing countries. Oats are a nutrient-rich food associated with lower blood cholesterol and reduced risk of human heart disease when consumed regularly. One of the most common uses of oats is as livestock feed; the crop can also be grown as groundcover and ploughed in as a green manure.
Description The oat is a tall stout grass, a member of the family Poaceae; it can grow to a height of 1.8 metres (5.9 ft). The leaves are long, narrow, and pointed, and grow upwards; they can be some 15 to 40 centimetres (5.9 to 15.7 in) in length, and around 5 to 15 millimetres (0.20 to 0.59 in) in width. Leaf blades emerge first from nodes in the stalk, then the sheath. New leaves grow upwards on nodes further from the ground, leaves on the old nodes gradually brown and wilt. Roots are fibrous, mostly in the uppermost 0.3 metres (0.98 ft) of the soil (though some may penetrate as deep as 1.5 metres (4.9 ft), and develop from a crown at the soil surface. When seeds are dense, they make only one or two hollow stems (culms), but when spaced out may make 10 to 30 culms. At the top of the stem, the plant branches into a loose cluster or panicle of about 10-75 spikelets. While they tend to self pollinate, 1-2% may outcross. There are 7-9 nodes, with one leaf at each node and hollow internodes. These contain the wind-pollinated flowers, which mature into the oat seeds or grains. Botanically the grain is a caryopsis, as the wall of the fruit is fused on to the actual seed. Like other cereal grains, the caryopsis contains the outer husk or bran, the starchy food store or endosperm which occupies most of the seed, and the protein-rich germ which if planted in soil can grow into a new plant.
Origins
Phylogeny
Phylogenetic analysis using molecular DNA and morphological evidence places the oat genus Avena in the Pooideae subfamily. That subfamily includes the cereals wheat, barley, and rye; they are in the Triticeae tribe, while Avena is in the Poeae, along with grasses such as Briza and Agrostis. The wild ancestor of Avena sativa and the closely related minor crop – A. byzantina – is A. sterilis, a naturally hexaploid wild oat, one that has its DNA in six sets of chromosomes. Genetic evidence shows that the ancestral forms of A. sterilis grew in the Fertile Crescent of the Near East. Analysis of maternal lineages of 25 Avena species using chloroplast and mitochondrial DNA showed that A. sativa's hexaploid genome derives from three diploid oat species (each with two sets of chromosomes); the sets are dubbed A, B, C, and D. The diploid species are the CC A. ventricosa, the AA A. canariensis, and the AA A. longiglumis, along with two tetraploid oats (each with four sets), namely the AACC A. insularis and the AABB A. agadiriana. Tetraploids were formed as much as 10.6 mya, and hexaploids as much as 7.4 mya. Crosses among tetraploid or hexaploid species are fully fertile, but diploid species vary in how they interbreed. Crosses among species with different ploidy may be sterile or partially fertile.
Domestication Genomic study suggests that the hulled variety and the naked variety A. sativa var. nuda diverged around 51,200 years ago, long before domestication. This implies that the two varieties were domesticated independently. Oats are thought to have emerged as a secondary crop. This means that they are derived from what was considered a weed of the primary cereal domesticates such as wheat. They survived as a Vavilovian mimic by having grains that Neolithic people found hard to distinguish from the primary crop. Oats were cultivated for some thousands of years before they were domesticated. A granary from the Pre-Pottery Neolithic, about 11,400 to 11,200 years ago in the Jordan Valley in the Middle East contained a large number of wild oat grains (120,000 seeds of A. sterilis). The find implies intentional cultivation. Domesticated oat grains first appear in the archaeological record in Europe around 3000 years ago. Oat seed dispersal is facilitated by two awns that are part of each seed head. After falling to the ground, these long, slender structures twist as they dry in sun and as they are re-moistened by dew and rain. As a result, the seeds moved along the ground until falling into gaps in the soil, essentially planting themselves. Domestication has selected for loss of awns, since seeds are now planted by humans, and larger seeds.
Agronomy
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