MU GENE ZOO

Small Grain Crops Garden


“Small grains” is a not a scientific term, but is used to describe a specific set of crop species. The term is also used in government documents and markets. Species referred to as small grain crops are cereal crops, which means that they are members of the grass family with an edible seed. The “small” in small grain crops refers primarily to plant size. Their plants are smaller than either corn or grain sorghum plants. Common small grain crops are wheat, oat, rye and barley. Although rice would fit the definition, it is usually not included in the small grain crops category.


The fruit of members of the grass family, including small grain crops, is a caryopsis. Caryopsis is a single-seeded fruit in which the pericarp (fruit wall) and seed coat are tightly fused. Small grain crops produce seeds that have small embryos and large endosperms.


Wheat

Wheat is by far the most important and widely grown small grain crop in Missouri, the U.S. and the world. Produced primarily as a human food crop, characteristics of the endosperm affect uses among the several wheat types.


The origin and domestication of wheat are more complicated than for many other agronomic crops and have led to several wheat species grown by humans. Origin most likely took place in a region that would become the modern countries of Iraq and Syria. The most common wheat species, Triticum aesitivum, have three distinct genomes. Each genome A, B and D, contains seven pairs of chromosomes. The A genome originated in a wild grass called Einkorn. Wild and domesticated einkorns (Triticum monococcum) exist today, but are cultivated in only a few places. Wild einkorn crossed with an unknown wild grass to produce a fertile species called emmer. This unknown grass was the origin of the B genome, so emmer wheats have both the A and B genomes. Wild and domesticated emmers exist today. Varieties within one of the market classes of wheat, durum, are closely related to emmer. Finally, wild emmer crossed with another wild grass, Aegilops tauschi (goatgrass), to produce a fertile species, Triticum aesitivum. Goatgrass was the origin of the D genome.


Market classes

Wheat varieties produced in the U.S. are categorized into one of several market classes or types. The classes have specific characteristics and often differ for primary use. Important characteristics are growth habit, kernel color and kernel hardness. Growth habit refers to the requirement for vernalization. Vernalization is the exposure of plants to cool temperatures so that they can flower and complete their life cycle. Wheat types that require vernalization will not flower without vernalization and are called winter types. Spring wheats do not require vernalization. Red color is controlled by three genes. The color compounds are located in the pericarp. Wheat types are usually classified as either red or white. Kernel hardness is classified as hard or soft. Starch granules in the endosperm of hard wheats are surrounded by protein. This causes cell walls to remain intact during grinding. Cell walls in the endosperm of soft wheat fracture during grinding.


Market classes in the U.S.:

  • Hard red spring. Endosperm contain a relatively large concentration of high quality gluten (protein). High quality gluten is elastic and allows for the capture of carbon dioxide in numerous and consistently sized bubbles. This results in light, fluffy breads. Primary use of hard red spring wheat is bread. The primary region of U.S. production is North Dakota, South Dakota and Montana.
  • Hard red winter. Endosperm contains a relatively large concentration of high quality gluten (protein). High quality gluten is elastic and allows for the capture of carbon dioxide in numerous and consistently sized bubbles. The results in light, fluffy breads. Primary uses for hard red winter wheat are bread and general purpose flour. This is the dominant market class in the country with production centered in Kansas.
  • Soft red winter. Endosperm contains less gluten protein than the hard wheats and does not produce light bread. Primary uses of soft red winter wheat are cakes, cookies and pastries. This is the market class grown in Missouri and the much of the U.S. east of the Mississippi River.
  • Durum. Endosperm is hard and glasslike. Although high in protein, the gluten quality is poor (does not stretch).├é┬áPrimary use of durum wheat is semolina flour and pasta. Durum is a spring wheat primarily grown in North Dakota.
  • Soft white. Endosperm contains less gluten protein than the hard wheats. Primary uses of soft white wheat are crackers and pastries. Center of production in the U.S. is the Pacific Northwest and New York.
  • Hard white wheat. This is the latest class to be established in USA. Endosperm is hard with medium amounts of protein. Hard white wheat is used for hard rolls, bulgur, tortillas and oriental noodles.



Morphology

Tillers are branches on grass plants and arise from stem nodes near or below the soil surface. Wheat plants produce up to four or more primary tillers and additional secondary tillers. Not all tillers will produce harvestable grain.


Leaves of grass plants contain a sheath and a blade. The sheath attaches the leaf to the stem node and often wraps around the stem. The area where the blade meets the sheath is called the collar. Wheat plant leaves possess a short membranous ligule and small, clasping, hairy auricles.


The name for a wheat inflorescence is spike, although they are often called heads. The spike contains a central axis called the rachis. Single spikelets are attached to nodes along the rachis and contain four to six florets (grass flowers) within a pair of glumes.


Awns are hair-like appendages that extend from lemmas and glumes. They contain chlorophyll, and because they are located at the top of the plant and close to developing seeds, they may provide sugars for grain filling. However, there is little difference, on average, for yield between awned and awnless varieties. Awns may have originated as a defense mechanism that limits animal grazing. In some wild species, awns help push seeds into soil as they twist in response to alternating wetting and drying.


Nearly all wheat types thresh clean. This means that the lemma and palea are removed from the grain during harvest. A subspecies of wheat called spelt is an exception. A ridged rachis prevents complete shattering of spelt spikelets and lemmas and paleas often remain attached through harvest. This increases the fiber content of products made from spelt.


Barley

Barley (Horedeum vulgare) is one of earliest domesticated crops. Its origin is most likely what is called the Fertile Crescent, an area what is now called the Middle East. Unlike wheat, barley has only one wild relative, H. spontaneum. Wild barley still can be found growing in southwest Asia and northern Africa.


Both winter and spring barley types exist. Winter barley requires vernalization. It is not as winter hardy as winter wheat, and this limits winter barley production in north and central areas of the U.S.


Like all small grain crops, barley produces tillers (branches from stem nodes close to or below the soil surface). Barley leaves have long, smooth auricles and an inconspicuous ligule.


The name for a barley inflorescence is spike, although they are often called heads. The spike contains a central axis called the rachis. Three spikelets are attached to each node along the rachis and each spikelet contains one floret surrounded by two narrow glumes. In six-row barley, all florets on each rachis node are fertile. Because of the alternating arrangement of rachis nodes, the barley spike appears to have six rows of grains. In two-row barley, only the center floret on each rachis node is fertile. The spike appears to have two rows of grains.


Nearly all barley varieties do not thresh clean. During grain-filling the lemma and pales become cemented to the pericarp. During harvest, the lemma and palea remain on the grain. A barley type called “hulless” or “naked” barley does thresh clean, but it is more of an oddity and not commercially grown.


The primary use of barley in the USA is livestock feed. Because it does not thresh clean, feed made from barley has more fiber than several other feed grains. Barley is used to make malt for use in the brewing industry. Malt is the source for amylase, the enzyme that digests starch into glucose so that yeasts can ferment and produce alcohol. A few human food uses exist including pearled (lemma and palea removed) barley in soups.


Rye

Rye (Secale cereale) likely coevolved with wheat and barley. However, rye was domesticated much later than wheat. A wild member of the Secale genus, S. montanum has been suggested as the wild relative of rye.


Most varieties of rye grown in the U.S. are planted in the fall. It is the most winter hardy of all of small grain crops.

Like all small grain crops, rye plants produces tillers (branches from stem nodes close to or below the soil surface. Rye leaves have short, smooth, pointed auricles and small or inconspicuous ligules.


The name for a rye inflorescence is spike, although they are often called heads. The spike contains a central axis called the rachis. Single spikelets are attached to nodes along the rachis and contain three florets (grass flowers) within a pair of glumes.


Food uses of rye are more common in Europe than in the U.S. Rye breads, including pumpernickel, are usually heavier than bread made from high quality wheat flour. The gluten in rye flour is poor quality and does not stretch. A small amount of rye is used in to make alcoholic beverages. A common use of rye in the U.S. is as a cover crop during fall, winter and early spring to protect soil from erosion.


Oat

Oat (Avena sativa), like rye, probably coevolved with wheat and barley. Also, like rye it was domesticated much later than wheat. Its wild ancestor is likely Avena sterilis.


Both winter and spring oat types exist. But, winter oat is the least hardy of the small grain crops and culture is limited to the southern U.S.


Like all small grain crops, oat plants produces tillers (branches from stem nodes close to or below the soil surface. Oat leaves have no auricles and prominent, short ligules.


Unlike the other three small grain crops, oat plants produce panicle inflorescences. A panicle is a branched inflorescence with spikelets attached with small stalks. Oat spikelets are large with several fertile florets.


Oat does not thresh clean during harvest. The lemma and palea remain attached. Products made from whole oat grains have the highest fiber content compared to all other small and coarse grain crops.

The primary use of oat in the U.S. is livestock feed. Human foods made from oat include oatmeal and rolled oats.


Triticale

Triticale is a human made cross between rye and wheat. The name comes from genus names for wheat (Triticum) and rye (Secale). The purpose was to combine the yield potential of wheat with the winter hardiness and disease tolerance of rye. Triticale has not been a commercial success and only small acreages in the U.S. are planted with triticale. Use is most common for forage.

 

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  MU Gene Zoo Small Grains: Contents

Wheat

Barley

Rye

Oat

Triticale