Cereal Grains
David S. Seigler
Department of Plant Biology
University of Illinois
Urbana, Illinois 61801 USA
seigler@life.uiuc.edu
http://www.life.uiuc.edu/seigler
OUTLINE
Importance:
•
to hunter-gatherers
•
to agricultural societies
Historical role:
•
how eaten
Botanical information:
•
distribution
•
systematics: Poaceae (Gramineae);
nearly 8,000 species, but only about
35 species cultivated.
•
anatomy-morphology
Properties
•
physical
•
nutritional
•
lysine
Human selection
•
replanting
•
harvesting methods
Some characters selected:
• tillers
• shortness
• non-shattering
• separation of fruits from
inflorescence
• disturbed habitat
• synchronous ripening
• more fruits
• larger fruits
• lack of sensitivity to day length
• glutinous properties (wheat)
Most important cereal grains today
• wheat - historical, today's perspective,
steps in origin, where and why
cultivated, disease problems- Near
Eastern origin
• rice - Asian and African species
• corn - Mexican origin
• sorghum - African origin
• most ancient cereal grain: barley
Reading
•
CHAPTER 5 IN TEXT
Introduction
• More than 70% of the world's farmlands devoted
to the cultivation of cereal grains.
• More than one half of the total calories consumed
by humans.
• Domestic animals fed primarily by cereal grains.
• Society as we know it could not exist without
cereal grains.
• Oldest of cultivated crops. Grasses used long
before that.
Courtesy Dr. Ted Hymowitz
• 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.
Grains in the grass family (Poaceae or
Gramineae).
• 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 grasses are edible.
Major grains and producers
• 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 and 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 humans.
Domestication
• As long as gatherers only gather, they exert
little selective pressure. The plants are
reseeded during the harvest by "shattering".
• 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.
Harvesting wild rice by traditional methods
Replanting
• The key factor in domestication was when
humans began to replant the seeds.
• Non-shattering, determinate growth, larger
and more seeds, increased inflorescence
size, fewer sterile flowers, tolerance for
disturbed habitat, and lack of seed dormancy
favored.
• Weeds adapted to disturbed sites.
• Related weeds may hybridize with the crop
plant.
• Eventually, the crop only survives
because of humans and vice versa.
• The major cereal grains are rice, wheat,
and corn.
Grasses
• Grass plants occur in all parts of the world.
• Monocotyledonous plants.
• Many grasses 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.
• Grass floral structures complex.
• Most grass flowers are perfect.
• Grass flowers borne in compound
inflorescences called spikelets.
• A floret is an individual grass flower.
(see pg. 112).
Grass flowers
• Superior ovary topped by two feathery
stigmas.
• Three stamens and three scale-like remnants
of petals.
• Each floret is enclosed in two bracts. The
inner is called the palea and the outer the
lemma.
• Nerves of lemma extend and are called an
awn.
• There are two more sterile bracts called
glumes.
• Fruit is a caryopsis.
• Food energy is stored as endosperm.
• The storage product is mostly starch, but
grains also have moderate amounts of
protein and some fats.
• Grains relatively low in water (10-13%). See
pg. 114.
• Many cultivated grasses are self-compatible
annuals that invest a large portion of their
energy as fruits.
Directions of selection of grains
One major change was grasses with tillers that
mature synchronously.
All plants and tillers mature fruits at the same
time.
The inflorescences have undergone even
greater change than the vegetative portions.
A single harvest that collects almost all the
seeds produced.
Shorter plants that don't lodge so readily.
• “Non-shattering” fruits. 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 nonshattering inflorescences.
• Separation of fruits from inflorescence parts
once stalks have been cut.
• Grains separate below attachment of bracts
or above them.
• The bracts are called "chaff".
• Removing the grains from the bracts is called
"threshing".
• The chaff is removed by winnowing.
• Removal of fruit walls or "pearling”.
Some important points
1. Cooking improves edibility. Most parched
or popped originally.
2. They store easily, are nutritious and
"concentrated".
3. They can be mechanically harvested.
Barley (Hordeum vulgare)
• Barley (Hordeum vulgare) is the earliest cereal to
have been domesticated. Cultivated 10,000 years
ago.
• Wild forms are all two row. The oldest cultivated
forms are also two row.
• This type of barley has one fertile floret in the central
spikelet of three at each node.
• By 6000 B.C., six row forms had appeared. Each
node has three spikelets and one floret in each
matures. See pg. 116.
Barley, Hordeum vulgare
• In barley, each node bears 3 spikelets, a
central one and two lateral ones.
• Each spikelet bears a single floret.
• In the 2 row types, 1 floret is fertile in the
central spikelet and one is sterile in each of
the two lateral spikelets.
• In 6 row types, all florets are fertile, one in
each of the three spikelets.
• Barley arose in the Near Eastern center.
• Also 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 are part of the same
operation.
• Barley was the major cereal until about 200
B.C. (2000 B.C. in the book). 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.
Wheat
• Wheat 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 arose that
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. urartu, or T. speltoides.
• One tetraploid was called emmer wheat
(Triticum turgidum) (see pg 117).
• A mutation in one variety caused the glumes
to collapse. Made separation of chaff easy.
• Tetraploidy gave rise to durum wheats (pasta)
(T. durum).
• This change also combined proteins in the
seeds to make gluten. Gluten is essential to
make bread of the style we know. Celiac
disease.
• Later, a hexaploid wheat arose. This
hexaploid called T. aestivum.
• The other parent seems to have been T.
tauschii.
• Has a hard endosperm and best for
bread making.
• Hexaploid wheat is not known to occur
in the wild.
• Winter and spring wheat.
• Most cultivars from wheat brought to the U.S.
by Mennonites in late 1800's from Russia and
the Ukraine.
• Wheat has lots of disease problems.
Puccinia graminis, or wheat rust.
• Production of cultivars with resistance is very
important, but it’s difficult to make hybrids.
• Resistant lines tend to last about three years
before disease catches up.
• Wheat mostly grown in cool, dry
climates. Moderate rainfall.
• Major crop in 5 continents. Russia,
Ukraine, midwest U.S., Canada, central
Europe, Turkey, Argentina, N.E. China,
N.E. Australia, N.W. India most
productive regions.
• The "green revolution".
• Bran and wheat germ is removed.
Winter wheat in Oklahoma
Harvesting wheat
Shocks of wheat
in Austria
Harvesting wheat
in Colombia
Rye (Secale cereale)
• Rye appears to have developed as a
cultivated crop from weeds in wheat and
barley fields.
• Fully domesticated about 3000 B.C.
• 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. Rye doesn't have gluten.
Rye, Secale cereale
Oats, Avena sativa
• Oats probably arose as a weed.
• 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.
Oats, Avena sativa
• 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.
Oats, Avena sativa
Rice (Oryza sativa)
• Rice 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. Previously
thought in India, Burma, Thailand, or Viet
Nam. New evidence suggests the Yangtze
valley in China.
• Other species of rice (e.g., Oryza glaberrima)
were domesticated in Africa.
• Rice in Thailand before 4500 B.C. and in
China by 3000 B.C. New data suggests as
early as 10,000 years ago.
• Rice widespread in India by 2000 B.C.
• Alexander the Great brought the grain back to
Europe from India about 300 B.C.
• By 15th century, rice was cultivated in both
Spain and Portugal.
• The Portuguese introduced rice into Brazil
and West Africa.
• In the 16th century, the English imported rice
from Madagascar.
• Rice an important crop in early South
Carolina (1647).
• Most rice in U.S. from Arkansas,
California, Louisiana, and Texas.
• Most rice (perhaps 90%) is grown and
consumed in the Orient.
Rice in Java
Rice cultivation in
the Orient
I. Polunin. Plants and Flowers
of Malaysia,
Times Editions, Singapore
1988.
Courtesy Dr. Dorothea Bedigian
Rice,
Oryza sativa
Rice
Threshing rice in Madagascar
• ”Long grain" and "sticky" types.
• Paddy and upland rice (Brazil the largest
producer of upland rice).
• Paddy rice is labor intensive. Mostly grown in
the Orient. Almost all mechanized in the U.S.
Planted by airplane.
• Most rice polished today. Many of the
nutrients lost. Causes vitamin B1 or thiamine
deficiency.
• In Asia and Africa, hybridization of rice with
"weed" strains causes serious problems by
reintroducing the shattering characteristic into
the crop type.
• Perennial rice species were harvested in S.E.
Asia before annual rice. They do not yield so
well.
• 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.
Wild rice, Zizania aquatica
A New World species, Zizania aquatica, has
long been wild harvested.
The inflorescences shatter.
The grain was collected by beating the mature
inflorescences into canoes.
In the late 1950's, farmers started cultivating
wild rice in Minnesota.
Plant breeders developed a non-shattering
variety recently.
Sorghum ( Sorghum bicolor)
•
•
•
•
•
Sorghum native to Africa.
Several domestication events involved.
Between 2200 and 4000 B.C.
Numerous cultivated types.
Used to feed animals (stalks), for grain and
for fiber (broomcorn).
• A plant of hot climates and low rainfall.
Sorghum ( Sorghum bicolor)
• Very important in India and in many areas of
Africa.
• Used to make bread (but doesn't rise), "pop"
sorghums, and beer.
• Used in the Southeastern U.S. to make a type of
molasses.
Sorghum, Sorghum bicolor
Johnson grass, Sorghum halepense
Millets
• Many grass cultivars that are locally important
crops in localized areas of the world.
• Millets especially important in areas of India.
• Among them, Eleusine coracana and
Pennisetum americanum are especially
important.
• See pg. 126.
A millet, Eleusine coracana
Courtesy Dr. J. M. J. de Wet
Corn or Maize
• 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 Aztecan, 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.
• Cultivation of corn in Mexico may go as
much as 7,000 years.
• Small cobs (1/2 inch long) have been
found in the Tehuacán valley and in
Tamaulipas.
• By 3000 (5000?) B.C., essentially
modern corn was being cultivated.
• New evidence based on phytoliths
suggests that essentially modern corn
arose in Mexico as early as 10,000
years ago.
• Corn was also cultivated in Peru by
about 7000 years ago.
• The greatest diversity for corn today is
in Peru, but wild ancestors are from
Mexico.
• In 1492, corn was cultivated from
Canada to Argentina.
• How did corn arise? Corn is related to
teosinte, Zea mexicana. Corn and
teosinte cross readily and teosinte is
found around corn fields in some parts
of Mexico.
• Teosinte is the major, if not the only,
ancestor of corn. See diagrams pg. 130
and 132.
Teosinte in Mexico
Courtesy of Dr. J. M. J. de Wet
Teosinte, Zea mexicana
Courtesy of Dr. J. M. J. de Wet
Teosinte ears and
seeds
Proposed origin
of maize ear
Yoking of corn kernels
Steps in the formation of corn ears
• Went from a fragile to a non-fragile ear.
• From 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.
Primitive corn ears
Corn or maize,
Zea mays
Male and female corn structures
Carolina Biological Supply Co.
Evidence for early
production of corn in
Peru
Phytolith images
http://phytolith.missouri.edu/RTF/Figures/Figure1.jpg
University of Missouri Phytolith Database
• Columbus took corn back to Europe on his
first voyage.
• The Aztecs ate corn treated with lime.
• In the southeastern U.S., Indians treated it
with wood ashes.
• These treatments partially hydrolyzed the
starches etc. Nixtamal or hominy.
• The Aztecs used nixtamal to make tortillas,
tamales, and chocolate drinks.
Posolero for
making posole
•
•
•
•
Corn is 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.
• Corn is now a major source of ethanol for fuel
in the U.S.
• 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.
Production of hybrid corn seed
• Before corn could be grown in the northern
U.S. and Canada, a loss of sensitivity to day
length 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.
Pseudocereals
Some pseudocereals are important today;
others have been extremely important in the
past.
Amaranthus was the second most important
crop in Mexico in early 1500's.
Because of its association with sacrifices and
religion, the Spanish tried to put down its use.
Cultivation of Amaranthus has survived until the
present.
• Many have advocated using amaranth as a
cultivated crop.
• Amaranth 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 PeruBolivia.
• In South America, these are called quinoa.
Grain amaranth, Amaranthus sp.
Amaranth cultivated in Bolivia.
Courtesy Dr. Tim Johns
Amaranth
infructescence and
seeds
Amaranthus retroflexus, a
weedy amaranth species of
Illinois
Pepitas, seeds of Cucurbita pepo Cucurbitaceae
Field with quinoa, a Chenopodium sp., in Bolivia
Courtesy Dr. Tim Johns
Winnowing quinoa and quinoa seed
Courtesy Dr. Tim Johns
Buckwheat, Fagopyrum
esculentum, Polygonaceae