CEREAL GRAINS



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CHAPTER 5 IN TEXT

Introduction
More than 70% of the world's farmlands devoted to the cultivation of cereal grains. Cereal grains provide more than one half of the total calories consumed by man. Not only humans, but also domestic animals are fed primarily by cereal grains.

Society as we know it could not exist without cereal grains. The only places that cereal grains are not too important is in a few areas of the lowland tropics, and in high Andean areas.
Grasses also are among the oldest of cultivated crops. They were used long before that.
Wheat and barley sustained the Near Eastern cultures, rice the Far East, corn the pre-Columbian New World cultures, and sorghum a number of African ones.
Contrary to some views, Rome likely fell (certainly in part) because of failing North African grain supplies.
Grains in the grass family (Poaceae or Gramineae). The one seeded fruit (a caryopsis) has a seed coat fused with the ovary wall. There are nearly 8000 species of grasses. The seeds of most are edible, although some are infected with endophytes and fungi.
Pseudocereals are non-grasses that produce similar fruits or seeds. Grain amaranth and buckwheat are examples.
The world's major grains are listed on pg. 110. The major producing countries are listed on pg. 110.
Artificial selection of grasses
Populations are variable. They are stable only for a given situation. A change in selection pressure will cause a change in the genetics of the plant involved.
Domestication is an evolutionary process under the influence of man. Usually a slow process. As long as gatherers only gather, they exert little selective pressure. The plants are reseeded during the harvest by "shattering". If anything, they would favor shattering types. This was true for grass harvesting by most of the North American Indians. They bent the grass over and hit the heads with a stick to loosen the grains. This would also favor ripening over time and seed dormancy.
The key factor in domestication was when humans began to replant the seeds. He then favored: non-shattering, determinate growth, larger and more seeds, increased inflorescence size, fewer sterile flowers, tolerance for disturbed habitat, and lack of seed dormancy. Weeds are adapted to disturbed sites and related "weeds" may hybridize with the crop plant.
Eventually, the crop only survives because of humans and vice versa.
Man favored non-shattering, determinate growth, larger and more seeds, tolerance to
disturbed habitat, and lack of seed dormancy.
  • The major cereal grains are rice, wheat, and corn.
    Grasses
    The grass plant occur in all parts of the world. They are monocotyledonous plants and differ in many ways from the generalized plant discussed in chapter 1. Grasses have fibrous roots. Many branch at the base and produce more or less equal sized stems called tillers. The leaf has a blade and a sheath that surrounds the stem or culm. The regions where the leaves originate are called nodes. See the diagram on pg. 112.

    Horizontal stems that grow along the ground are called stolons. Vegetative reproduction is common in perennial grasses. Grass floral structures are even more complex. Most grass flowers are perfect. Grass flowers are borne in compound infloresences called spikelets.
    A floret is an individual grass flower. (Again see the diagram on pg. 112).
    There is a superior ovary topped by two feathery stigmas. There are three (occasionally 6) stamens, and three scalelike remnants of petals. Each floret is enclosed in two bracts. The inner is called the palea and the outer the lemma. The nerves of the lemma extend and are called an awn. There are two more sterile bracts called glumes.
    The fruit is called a caryopsis.
    The major portion of the food energy is stored as endosperm.
    The storage product is mostly starch, but grains also have moderate amounts of protein and some fats.
    They are relatively low in water (about 10-13%). See the table on page 114. Many of the nutrients (especially protein and fat) are found in the aleurone layer just inside the bran of the fruit (see pg. 114).
    Many grasses are self-compatible annuals that invest a large portion of their energy as fruits.

    Directions of selection of grains.
    One major way in which humans have modified grains is selection for grasses with tillers that mature synchronously. That way the plants all mature fruits at the same time, and a single harvest collects almost all the seeds produced. In other crops (such as maize and sorghum) there has been selection for plants that don't branch. Humans also have selected recently for shorter plants that don't lodge so readily. This is especially important in wet tropical regions of the world.
    The inflorescences have undergone even greater change than the vegetative portions. One of the major changes is "non-shattering" fruits. The fruits stay on the plant when they are mature. Good for humans when they harvest grains, but not good for seed dispersal for wild plants. These seeds became preferentially collected and replanted.
    All major cereal grains now have non-shattering infloresences.
    Another major change was the ease of separation of the fruits from the infloresences once the stalks have been cut.
    Grains can separate below the attachment of the bracts or above them. The bracts are called "chaff". Removing the grains from the bracts is called "threshing". The chaff is removed by winnowing. Separation of portions of the fruit walls is even more difficult. This has been done and is still done by "pearling" or abrading the coat off.


    Some important points:
    1. Cereal grains feed most of the world.
    2. They are important in all cultures.
    3. They were harvested by "gatherers".
    4. Cooking improves edibility. Most parched or popped originally.
    5. They store easily, are nutritious, and "concentrated".
    6. They can be mechanically harvested.
    7. Steps of domestication:
        • Populations are variable.
        • Selection pressure was exerted by man.
        • The method of harvesting was important.
        • Replanting was a key step.
      Barley
      Barley (Hordeum vulgare) is the earliest cereal to have been domesticated. It was cultivated 10,000 years ago. Wild form are all two row. The oldest cultivated forms are also two row. This type of barley has one fertile floret of three in each spikelet on the flowering stalk. By 6000 B.C., six row forms had appeared. Each node has two spikelets. Each of three florets in a cluster matures. For illustration see pg. 116.
      Each node bears 2 spikelets. Each spikelet bears three florets. In the 2 row types, 2 are sterile in each spikelet. In 6 row types, all are fertile. Although barley arose in the Near Eastern center, it probably also was domesticated in China and Tibet and in Ethiopia.
      Originally made into a paste and baked. When soaked in water to make the grain more digestible, fermentation was discovered. Baking and brewing became part of the same operation.
      Barley was the major cereal until about 200 B.C. (2000 B.C. in the book) when it was supplanted by tetraploid wheat. About half in U.S. used to feed livestock another fourth used to make beer and whiskey. Worldwide, barley is now the number four cereal grain.


      Barley

      Wheat
      Wheat is not quite as old as a cultivated crop as is barley. Wild and early domesticates of wheat were diploid (2n = 14) (Triticum monococcum). Early in domestication, a mutation suppressed shattering. Wheat with this mutation quickly became the major cultivated type. Today called einkorn wheat. By 8th century B.C., einkorn and another species hybridized and produced a tetraploid wheat. The other species could have been T. searsii, T. longissima, or T. speltoides. T. speltoides was once a major wheat in Europe. One tetraploid was called emmer wheat (Triticum turgidum) (see pg 117). One variety had a mutation that caused the glumes to collapse. This made separation of the chaff easy and gave rise to durum wheats (good pasta is made from these wheats).
      This change also combined proteins in the seeds to make gluten. Gluten is essential to make bread of the style we know.
      Later, a hexaploid wheat arose. The other parent seems to have been T. tauschii. This hexaploid called T. aestivum. Has a hard endosperm and best for bread making. Hexaploid wheat is not known to occur in the wild.
      Winter and spring wheat. Most of our good wheat cultivars are derived from wheat brought to the U.S. by Mennonites in late 1800's from the Russia and the Ukraine.
      Wheat has lots of disease problems.Puccinia graminis, or wheat rust, is one of the worst of these. Production of cultivars with resistance is very important. They tend to last about three years before disease catches up. Difficult to make hybrids.
      Wheat grown in cool, dry climates most. Moderate rainfall. Major crop in 5 continents: former USSR, midwest U.S., Canada, central Europe, Turkey, Argentina, N.E. China, N.E. Australia, N.W. India most productive regions.
      The "green revolution". Why it did not work as well as planned. A 60 lb. bushel of wheat gives 42 lbs. of flour after milling. Bran and wheat germ is removed.


      Wheat 1
      Wheat2

      Rye
      Rye (Secale cereale) appears to have developed as a cultivated crop from weeds in wheat and barley fields. It was fully domesticated about 3000 B.C. Also native to southwest Asia. Rye can grow in colder areas than almost any other cereal grain. Grows well in northern Europe.
      Rye bread almost always contains wheat as well as rye because rye doesn't have gluten need to make light bread.

      Triticale
      A hybrid of wheat and rye. Can grow where no other cereal grains grow. Very cold tolerant. Dates back to 1875, but only popular in last 10-20 years.

      Oats
      Also probably arose as a weed. Probably the last of the major cereals domesticated in the Near East. Perhaps as late as 1000 B.C. Also now a hexaploid oat, Avena sativa. No longer known in the wild.
      Typically grown in cold areas to feed animals. Disease resistance limits use in warmer parts of the world. Used by Romans. They called the Germans "oat eating barbarians". Oats are high in protein and fat. Often used to feed horses. This is the "national grain of Scotland".

      Rice
      Rice ( Oryza sativa) feeds more people than any other crop. 1.7 X 109 people eat rice as their major food plant daily. Most important in the orient. Although originally domesticated in Asia, the exact site of origin is uncertain. Probably in India, Burma, Thailand, or Viet Nam. Other species of rice (e.g., Oryza glaberrima) were domesticated in Africa.
      In Thailand before 4500 B.C. and in China by 3000 B.C. Rice was widespread in India by 2000 B.C. Alexander the Great brought the grain back to Europe from India about 300 B.C. By the 15th century, rice was cultivated in both Spain and Portugal. The Portugese introduced rice into Brazil and West Africa. In the 16th century, the English imported rice from Madagascar. Rice became an important crop in early South Carolina (1647). Most rice in the U.S. is from California, Arkansas, Louisiana, and Texas. Most rice (perhaps 90%) is grown and consumed in the orient.
      Both "long grain" and "sticky" types. Paddy and upland rice (Brazil the largest producer of upland rice).
      Paddy rice labor intensive in the orient, but is almost all mechanized in the U.S. Planted by airplane. Most rice polished today. Many of the nutrients lost. Caused vitamin B1 -deficiency.
      Perennial rice species were harvested in S.E. Asia before annual rice. They do not yield so well. Although we think of rice as being cultivated all over S.E. Asia, rice was not an important crop in much of Indochina, the Philippines, and Indonesia until about a century ago. This is partly linked to the production of new non-lodging varieties.
      Asian rice was introduced into Africa where it has displaced native rice cultivars.
      In both Asia and Africa, hybridization of rice with "weed" strains causes serious problems by reintroducing the shattering characteristic into the crop type.


      Rice
      Rice2

      Wild rice
      A new world species, Zizania aquatica, has long been wild harvested. It was never domesticated until very recently. The inflorescences shatter. The grain was collected by beating the mature infloresences into canoes. In the late 1950's, people started cultivating in Minnesota. Plant breeders were finally able to come up with a non-shattering variety.

      Sorghum
      Sorghum ( Sorghum bicolor) is native to Africa. Harlan feels there were several domestication events involved in the formation of this grain. Somewhere between 2200 and 4000 B.C. Numerous cultivated types. Some used to feed animals (stalks), some for grain, some for fiber (broomcorn), etc.
      A plant of hot climates and low rainfalls. Very important in India and in many areas of Africa. Used to make bread (but don't rise), "pop" sorghums, and beer. Used in the Southeastern U.S. to make a type of molasses.


      Sorghum


      Millets
      This term refers to many different grass cultivars that are locally important crops in some areas of the world. They are especially important in areas of India. Eleusine coracana and Pennisetum americanum are especially important. A table of millets is given on page 126.

      Corn or Maize
      Often called maize (Zea mays) is a New World crop. The only major cereal grain domesticated in the New World. Corn was the major food plant of all major New World civilizations, e.g., the Mayan, Incan, and Aztec, although Amaranthus was also important in some regions. See diagram p. 130.
      Many American Indians planted squash, corn and beans. This provided a relatively balanced diet.
      Corn pollen goes back possibly 80,000 years. Cultivation of corn in Mexico goes back at least 5000 (7000?) years. The small cobs (1/2 inch long) have been found in the Tehuacán valley. Also in caves in Tamaulipas. By 3000 (5000?) B.C., essentially modern corn was being cultivated. About 1000 B.C., before a stable agricultural society arose at Tehuacán. Corn was cultivated in Peru by 2000 B.C. At the time of Columbus, corn was cultivated from Canada to Argentina.
      The greatest diversity for corn today is in Peru, but wild ancestors in Mexico. How did corn arise? Corn is related to teosinte, Zea mexicana, and many people have felt that teosinte was the principal ancestor of corn. It has been thought by some that corn acquired some genes from grasses of the genus Tripsacum. Others have said that corn is derived from "primitive corn", although occasional hybridization and introgression with other species may have been involved. More recent evidence makes it more clear that teosinte is the major, if not the only, ancestor of corn. See diagrams pg. 130 and 132.
      Corn and teosinte cross readily and teosinte often is found around corn fields in Mexico. Hugh Iltis has recently proposed that corn arose from feminization of a male inflorescence on a lateral branch and not from the female teosinte ear. This is a catastrophic sexual transmutation. See the diagram on page 132.
      There are numerous corn flowers. Columbus took corn back to Europe on his first voyage. Corn has never become as popular in Europe as it is in North America. The Aztecs ate corn treated with lime. In the southeastern U.S., Indians treated it with wood ashes. This partially hydrolyzed the starches etc. Made nixtamal or hominy. The Aztecs used it to make tortillas, tamales, and chocolate drinks.
      Corn deficient in lysine and tryptophan. Most corn in the U.S. fed to animals. Corn starch used to make syrup. Corn is now one of the major sugar producing plants of the U.S.
      Today, almost all corn cultivated in the U.S. is hybrid corn made by using inbred, highly homozygous lines. This is easy because corn is monoecious. In 1935, only 1% hybrid corn used. Mostly single cross now but double cross method also important. Went from a fragile to a non-fragile ear, spikelets suppressed to both spikelets fertile, ear two ranked to four ranked, glumes hard to glumes soft, glumes cover seed to glumes short, seed imbedded in rachis to seed exposed, seed small to seed large.
      Before corn could be grown in the northern U.S. and Canada, a loss of sensitivity to daylength also had to occur.
      Major types of corn: flint corn (N.E. U.S. Indians); dent corns (S.E. U.S., high yielding, soft starch); flour corns (soft starch, S.W. U.S. Indians, easy to grind by hand); sweet corn (high in sugar, eaten green) and popcorn (done to make corn more palatable).
      Major producers. See table in book.
      Primitive corn ears
      Primitive corn
      Corn (maize)
      Teosinte seed
      Teosinte fruiting axis

      Pseudocereals
      Some pseudocereals are important today; others have been extremely important in the past. Amaranthus was the second most important crop in Mexico when the Spanish arrived in the early 1500's. Because of its association with sacrifices and religion, the Spanish tried to put down its use, but cultivation of Amaranthus has survived until the present.
      In recent times, many have advocated using this as a cultivated crop and it is nutritious and can be cultivated with most modern farm equipment with some modifications. The major problems are lack of an established market and public acceptance.
      Several species of Chenopodium also have been cultivated in both Mexico and in Peru-Bolivia. In South America, these are called quinoa.


      Amaranthus heads
      Amaranthus seeds



      Revised January 2005


      © David S. Seigler, Integrative Biology 363, Plants and Their Uses, Department of Plant Biology, 505 S. Goodwin St., University of Illinois, Urbana, Illinois 61801 USA. E-mail seigler@life.uiuc.edu Telephone 217-333-7577.

      Lecture slides (Cereal grains)

      Lecture slides (Pseudocereals)

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