Cereals - the Staffs of Life

 

I.  Importance

• Rice, maize, wheat - top three main crops worldwide

• Cereals are among the first cultivated crops (barley, wheat, maize)

• Granaries - important part of most cultures

• Every culture, with the exception of high Andes, developed a cereal

• Main food source for approx. 2 billion people

• Named for Ceres - Goddess of crops

II.  Why are cereals so important?  
    They are important because: 

1. easily stored; 

2. easily transported; 

3. resist spoilage (i.e., low moisture); 

4. nutritious; 

5. highly caloric (provide at least one half of the worlds calories); 

6. high yielding; 

7. seeds in a cluster making them easy to harvest; 

8. easily grown, most are self compatible

III.  What is a cereal?

1. Taxonomy.
       Member of the grass family (Poaceae, also called Graminae)
   

2. Habit:
       Grasses can be annual or perennial.  
    

3. Roots:  
       The roots of grasses are fibrous, which makes them good soil binders and the reason they are planted for erosion control.
    

4. Stems:
       Grass stems are called culms.  These are usually hollow, except at the nodes.  Branches that originate from near ground level are tillers.  Many grasses have a rhizome, stolon, etc.
    

5. Leaves:
       Typically alternate and in one plane.  The leaf is made of three parts; blade, sheath and ligule.  The sheath is usually not fused around the stem, but rather is open.  The ligule is a small tissue found between the blade and sheath.  It can be hairy, membranous, even absent, and is important taxonomically.  There may also be auricles present, which are small ear‑like appendages at the junction of sheath and blade.
   

6. Flowers:  
       Perfect and imperfect (plants usually monoecious, rarely dioecious).  The petals and sepals are absent, reduced to lodicules.  There are 2 - 3 lodicules  per flower.  The function of the lodicules is to open up the flower (they absorb water and swell pushing apart the bracts surrounding the flower).
   

7.  Androecium:  
       Usually three stamens, these typically dangle out of the flower at maturity.
   

8.  Gynoecium:  
       The pistil has 2, feathery styles.
   

9. Pollination:  
       Grasses are adapted for wind pollination.  Adaptations for wind pollination:  copious amounts of pollen, plumose stigmas, anthers stick out of the flower when the flower is mature.
   

10.  Fruit:  Caryopsis or grain, single seeded fruit in which fruit wall and seed coat are fused and indistinguishable from one another. 
    
        Parts of the grain:  embryo (germ) - rich in oil/protein; endosperm - rich in starch; aleurone layer - protein/oil, secretes enzymes to initiate germination; bran - fruit and seed walls.  Polished grain - removed bran and aleurone.  One advantage is that the grain will not spoil as readily; the disadvantage is that it removes much of the nutrional value of the grain.
    

11.  Inflorescence:  
        The flowers are subtended by modified leaves called bracts.  The outer bract (lemma) may form an extension called an awn.  The palea is the inner bract. It is generally smaller, oriented toward the main stem axis, and 2 veined.  A flower with lemma and palea is a floret. 
    
        Florets are arranged in clusters called spikelets.  The bottom pair of bracts of a spikelet are sterile (no flower in axil) and are called glumes.  A spikelet may be comprised of from one to many florets.  The inflorescence is considered to be an arrangement of spikelets rather than individual flowers.

IV.  Pseudocereals 
    Plants that bear a superficial resemblance to the true grasses and/or have seeds that do and are used in similar ways as cereal grains.  Examples are Amaranth, quinoa (Chenopodium quinoa) and buckwheat (Fagopyrum esculentum)

V.  Domestication/Selection of cereals
    The following is a series of trends in the domestication of cereals (these were also discussed in our Origin of Agriculture class)

1. Dwarf plants - minimize lodging

2. Unbranched - more grains per stalk and more synchronous ripening

3. Synchronization of ripening

4. Synchrony of tiller formation - ease of harvest, maximize yield

5. Fruit retention - eliminate shattering

6. Ease of threshing and winnowing - threshing is the process of separating the grain from the bracts (chaff); winnowing is the process of removing freed grain from the chaff.  Traditional methods vs. modern. 

7. Increase grain size and quality

 VI.  Maize (Zea mays)

1. Taxonomy.  
       Commonly called corn in N. America.  However, corn is a generic name for any cereal in some parts of the world (i.e., Britain).
   

2. General anatomy.
       Tassel (male flowers) , silks (styles, female flowers), monoecious, imperfect flowers, ear - lateral shoot, short internodes, subtended by up to seven leaves (husks).
    

3. Types of maize - based upon the type and distribution of starch in the grain, and the shape of the kernel (which is related to starch content).  

   Popcorn - mostly hard starch (low water content) that surrounds a small pocket of soft starch (high water content).  The grain "pops" when from steam from the soft starch.   Flour - primarily soft starch.  Good for grinding.  Flint - mostly hard starch.  Flour and flint corns were the major types grown when the Europeans arrived.  They are little cultivated now. Dent - central core of soft starch surrounded by hard starch.  When it dries, the soft starch shrinks more leaving a dent in the top of the kernal.  Main field type corn in US    Sweet corn - sugar is in the form of sucrose, not starch.  When dried it shrivels up. Waxy - contains hard and soft starch with higher fat content.  Pod corn -  each grain is surrounded by a husk.

4. Uses.
       Countless.  Food, silage,  fermented into beverages (beer, bourbon) and gasoline additives, corn syrup, cellulose for rayon
   
   

5. Domestication.
       Where did maize come from and how did it evolve?   

 VII.  Wheat (Triticum sp.)

1. Domestication.
       Evidence for wheat as early as 8-7,000 BC; domesticated in Near East
   
   

2. Types of wheat  
   
   Einkorn (Triticum monococcum).  
       This was the first cultivated wheat.  Wild forms (they shatter) are known).  It has 14 chromosomes (2n = 14).   
   
   Emmer (Triticum turgidum).  
       This is a hybrid between einkorn and a wild wheat and resulted from a doubling of the chromosomes.  It has 28 chromosomes (4n).  
   
   Durum (Triticum durum).
       Probably a mutation that was derived from emmer wheat.  The main differences between emmer and durum is that durum wheat is:  (a)  free threshing; and (b) good quality protein (gluten).  Makes semolina flour that is used extensively in pastas.  Grown in northern US especially ND and Canada.  Has 28 chromosomes (tetraploid).   
   
   Bread (Hard/Soft, Red or Club; Triticum aestivum).
       This is the major wheat in cultivation.  It has a high protein content and good gluten.  It has 42 chromosomes - is a hexaploid and is a result of a cross with Aegilops squarrosa.   

   Hard wheats have a higher protein content, require less rain, used for breads  Soft wheats produce a softer flour, require less rainfall, used for pastries  Spring wheat - planted in spring, harvested in fall Winter wheat - planted in summer, harvested following summer. These wheats must overwinter in order to flower and produce grains.  This required cold treatment is called vernalization.

3. Wheat Success.
       The success of the wheat crop in the US was dependent on:   

   Overcoming wheat rust (Puccinia graminis) - a fungus that infects the wheat plant and lowers yields.  Wheat rust has two hosts; the other is barberry.  It was thought that the destruction of wild barberry plants growing near wheat would be a good way to combat this disease - but it didn't prove too successful;  Introduction of drought and lodging resistant varieties; and Development of flour mills.          White flour - remove bran and germ, less nutritious but better storage.  Whole wheat - leave bran and germ but spoils more readily.  Whole wheat flour is reasonably nutritious.  It has a good quality protein, and is just missing vitamin A, B12, C and iodine (these are usually added backed to "enriched" flours).  Traditionally the grain was parched to remove the bran, but this ruined the grain and quality of the gluten.

VIII.  Rice (Oryza sativa)

1. General - sacred symbol of fertility in the Orient; extremely important crop, perhaps one of most important; domesticated in Asia (Thailand/Burma) around 7000 BC.  Feeds more people than any other cereal.  
   

2. There are two sub-species of rice: 
   
   1.  Oryza sativa var. indica - Long grain.  This is dry, separates on cooking.  Grown in tropical and subtropical areas.  The amylopectin content is greater than the amylose content.  
   
   2.  Oryza sativa var. sativa - Japonica or short grain rice.  Soft and gluey texture because of amylopectins and dextrose.  More temperate.
   

3. Cultivation.
       Rice requires much water.  Upland rice - wet but not standing water;  Paddy rice - prefers standing water.   Most of the world's rice is grown in paddies.  Air chambers in the stem help to move oxygen (air) to the roots that are embedded in the rather anaerobic (oxygen-free) soils.  An aquatic (floating) fern (Azolla) is often cultivated with rice as a type of green manure.  Azolla is able to fix nitrogen and act as a natural fertilizer for the rice.  Traditionally, seedlings are individually planted in the paddies.  In the US, rice is usually seeded directly in the field, sometimes by airplane.
   

4. Processing.
       White rice - remove bran and seed coat.  Polished rice - removes bran, seed coat embryo and aleurone layer.  Obviously removes most of the nutrients.  Beri-beri - deficiency of vitamin B1 (source of thiamine).

IX.  Rye (Secale cereale)

• Native to SW Asia. 

• Originally a seed in barley fields = secondary crop

• domesticated about 3000 BC

• very hardy - cold & drought tolerant

• used for forage, feed, erosion control, fermented to whiskey

• common host for ergot 

X.  Triticale (Triticosecale)

• wheat x rye hybrid

• higher yield and nutritionally superior

XI.  Oats (Avena sativa)

• last domesticated cereal (ca 1000 BC)

• Eastern Mediterranean

• secondary crop

• mostly used as a forage crop

XII.  Barley (Hordeum vulgare)

• first domesticated cereal 7-10,000 ybp in Fertile Crescent (Iran, Iraq, Turkey)

• 2 row vs. 6 row

• pearled - rubbed against disks

• initially used in pastes, toasted, porridges, breads, beers

• about half of crop feed to cattle, one quarter for beer making

XIII.  Wild Rice (Zizania aquatica)

• New World (i.e., MN)

• wild, now paddy grown

XIV.  Sorghum (Sorghum bicolor)

• native to Africa

• domesticated 2-4000 BC

• Types:  (a) grain - food; (b) sweet or sorgho - animal feed; (c) Sudan grass; (d) broom corn

• molasses, flat breads

• hot regions, tolerates low rainfall