© T. M. Whitmore

TODAYMaya Corn God

READINGS:Plants and Society (reserve) pp 197-203; 259-260Omnivore’s Dilemma: 15-64; 85-99

Readings for Next week:Nature’s Metropolis pp 205-259On line in Contemporary issues… folder: “Power Steer” (M. Pollan) Amber Waves article on Hispanic workersOmnivore’s Dilemma 65084, 185-238Hungry Planet pp 22-29 (Australia outback); 162-165; 266-275 (USA)

© T. M. Whitmore

Questions re Last Time• “The Green Revolution”

© T. M. Whitmore

Problems & Successes continued

• Impacts on large and small holdersDifficult for poor to afford the “package”Benefits of improved output mostly to

the already relatively better off

• Other criticisms Genetic lossPetroleum dependence (fertilizer)Dependence on irrigationDoes not “solve” the food problem

© T. M. Whitmore

Maize• Maize is a grain bearing grass family plant (like

all other grains) – but unlike any other

• Through selection humans have created a plant that no longer has the ability to disperse seeds and produce offspring without human intervention

© T. M. Whitmore

Controversy in origin of maize

• The Maya considered corn a gift from the gods and cultivating it was a sacred duty

• Botanists, however argue: Battle of Titans:Mangledorf and Beadle1930s through 1970s

© T. M. Whitmore

Paul Mangledorf: Tripsacum school

• He argued that:Domesticated maize was the result of a

hybridization event between an unknown wild maize from S America and a species of gamma grass, Tripsacum.

Teosinte (a wild grass found in C. Mexico) was of hybrid origin, the offspring of a cross between another genus of grasses (Tripsacum) and maize.

Paul Mangelsdorf George Beadle

Robert Soreng @ USDA-NRCS PLANTS Database

Tripsacum latifolium L. (gamagrass)

Immature ears of Zea diploperennis (a variety of teosinte) whole and sectioned with a few mature fruitcases, one of which is cracked open to expose the grain (photo by Hugh Iltis)

© T. M. Whitmore

Teosinte• The accepted wisdom up to the 1970s was that

the morphological differences between teosinte and maize were simply too great for maize to have been selected from teosinte by ancient peoples over a few thousand years.

• Thus teosinte was placed in the genus Euchlaena in the 19th century rather than in Zea with maize (Z. mays)

© T. M. Whitmore

George Beadle: Teosinte school

• He argued that Some teosintes were of the same species as

maize, while others belonged to a distinct species

A Mexican annual teosinte (Zea mays ssp. parviglumis) was the direct ancestor of maize.

A small number of major mutations could have converted this teosinte into a useful food plant during the early stages of domestication.

© T. M. Whitmore

Battle Decided• Maize is a direct domesticate of a teosinte (Zea

mays ssp. parviglumis), native to the Balsas River Valley area of southern Mexico

• With up to 12% of its genetic material obtained from another teosinte species Zea mays ssp. mexicana through introgression.

© T. M. Whitmore

Teosinte II• The teosintes make up a group of large grasses of

the genus Zea found in Mexico, Guatemala and Nicaragua.

• Virtually all populations of teosinte are either threatened or endangered

• Much scientific interest in conferring beneficial teosinte traits, such as insect resistance, perennialism and flood tolerance, to cultivated maize lines, although this is very difficult due to linked deleterious teosinte traits.

Teosinte and "reconstructed" primitive maize. (photo by John Doebley)

Photos courtesy of the Doebley Lab, Department of Genetics University of Wisconsin-Madison

Ears of Zea mays ssp. parviglumis (maize’s teosinte ancester) and maize (photo by Hugh Iltis)

Zea mays ssp. mexicana (teosinte) plant

(photo by Hugh Iltis)

Wild form of Zea mays ssp. mexicana plants growing in a field in Michoacan, Mexico (photo by John Doebley)

Geneflow from teosinte (maize wild relative) to maize.

Jarvis, Devra I. and Toby Hodgkin

Teosinte ear (Zea mays ssp mexicana) on the left, maize ear on the right, and ear of their F1 hybrid in the center

(photo by John Doebley)

© T. M. Whitmore

Maize Domestication• Maize development is thought to have

started from 7,500 to 12,000 years ago

• Archaeological remains of the earliest maize cob, found at Guila Naquitz Cave in the Oaxaca Valley of Mexico, date back roughly 6,250 years

• > 200 varieties in the Americas by 1492 (amazing breeding achievement).

© T. M. Whitmore

Maize genetics• A distinguishing feature of this grass is the

separation of the sexes among its flowering structures.

• Unlike other grasses, which produce perfect (bisexual) flowers, maize produces male inflorescences (tassels) which crown the plant at the stem apex, and female inflorescences (ears) which are borne at the apex of condensed lateral branches

The International Institute of Tropical Agriculture (IITA)

© T. M. Whitmore

Maize genetics II• Maize is open pollinated (wind blows copious

pollen from stamen to ovaries) most other grains are not

• Fields of wheat or rice will be more or less homogeneous generation after generation – (when planting saved seed); not so for maize since it can cross breed so easily with other varieties that may be growing nearbyThis may be a plus since the new accidental

crosses may have better yield or other beneficial traits

But also a negative since the new cross may be worse

© T. M. Whitmore

Maize genetics III

• The high productivity of maize is due to its large leaf area and to its C4 photosynthetic pathway

• C4 trait (shared by other tropical species adapted to survive periods of drought stress)Is a more efficient means of exchange of

water vapor for atmospheric CO2

• C4 species can produce more dry matter per unit of water transpired than can plants endowed with the conventional (C3) photosynthetic pathway.

© T. M. Whitmore

Maize genetics IV

• Maize’s cross-pollinating has contributed to its broad morphological variability and geographic adaptability

• Varieties may range from 0.5 - 5 m height• Mature in 60 to 330 days • Produce 1 to 4 ears per plant (depends on

density planted)• 10 to 1,800 kernels per ear (each of which

could make a new plant)

© T. M. Whitmore

Maize genetics V• Yield from 0.5 to 23.5 tons of grain per

hectare• Kernels may be colorless (white) or yellow,

red, blue or variegated with these colors in mottled or striated patterns.

• Produced from 50° latitude N to 40° S, is adapted to desert and high rainfall environments, and to elevations ranging from 0 to 4,000 meters above sea level.

© T. M. Whitmore

Maize genetics VI• There is high genetic biodiversity in the

Mexican maize pool, a factor of great importance for the breeding of current and future maize cultivarsat least 42 landraces in 3 groups

A sample of the diversity represented in the corn crib of one farmer in the highlands of central Mexico.

(photo by Hugh Iltis)

© T. M. Whitmore

Major maize phenotypes (groups of varieties)

• Dent corn Most produced type globally = 73% of

commercial production, Yellow dent = “field corn”

Used as livestock feed and for industrial manufactures (starch, corn sweetening, oil, alcohol)

Some white dents are used for human foods in USA, e.g., breakfast cereals, and grits

Produces higher yields and dominates production in North America

© T. M. Whitmore

Major maize phenotypes II• Flour corn (usually white)

The preferred form for direct human consumption

Soft starch that is easily ground to produce meal that can be consumed directly, or as a flat bread, dumpling or beverage

Currently accounts for 12% of commercial production

• Popcorn - the original domesticated type• Flint corn –produced in areas where cold tolerance

is required (e.g., Italy for polenta) and is often preferred for hand grinding

• Sweet corn – AKA corn on the cob

Minnesota State University, Mankato

White flint on left, modern hybrid dent in middle, and Yellow Northern Flint

© T. M. Whitmore

Hybrid corn: World’s 1st Biotechnology

• Windborne pollen effects fertilization of open-pollinated varieties: there is no control of the male parentage

• Thus the drive to develop inbred lines. These are developed by a combination of inbreeding and selection. Inbreeding to transfer of pollen from an

individual plant to the silks of the same plant.

This process is repeated for several generations until the strain becomes stable, or true breeding.

© T. M. Whitmore

Hybrid corn II • A geneticist, G.H. Shull, in 1906

Noted the reduction in “hybrid vigor” (heterosis) in inbred varieties and

Restoration of vigor upon cross breeding inbred varieties

• Cross-breeding involves the cross breeding of selected parents“Single crosses” are produced by

crossing two inbred lines. “Double crosses” are produced by

crossing two different single crosses.Selection is practiced in each generation

to maintain only the superior types.

© T. M. Whitmore

Hybrid corn III • Aim of modern hybrids is to produce a

plant with reliable characteristics (e,g., yield) and modify the local ecology to fitThis is opposite from traditional breeding

that aimed to breed a local variety to fit well with local environmental conditions

© T. M. Whitmore

The shift to hybrids• By 1930s seeds of "double cross" hybrids

could be produced at a price US farmers could afford.

• Farmers could take advantage of the benefits of hybrid corn varieties that resulted in an increase in vigor, yield, and uniformity

• But until the 1940s most farmers still were growing open-pollinated (OP) varieties

• But by 1956, all of the Corn Belt and 90 per cent of the U.S. corn land was in hybrids.

© T. M. Whitmore

The shift to hybrids II• The shift from OPs to hybrids occurred

because hybrids were higher yielding (more corn on fewer

acres)Stood up better (i.e., resisted lodging)Were more tolerant to stresses (drought,

diseases, insects)Had greater uniformity – they were

better suited for mechanical corn pickingThe grain quality was better

• But, saved seeds from these hybrids do not necessarily breed true in farmers’ fields

© T. M. Whitmore

The shift to hybrids III• The introduction of hybrids also allowed, for

the first time, a cost effective protection of intellectual property in corn breeding

First public institutions (ag schools such as NCSU) but later private firms did the costly work to produce these hybrid seeds

• Farmers buying the seed could not maintain or recreate the hybrid themselves and thus needed to buy seed each year if they wanted to maintain the yield advantage the corn hybrids provided.

© T. M. Whitmore

Consequences of the shift to hybrids

• Hybrid corn was and is a huge scientific and commercial success.

• There were, however, unforeseen consequences of this technology. Existing (and genetically diverse) open-

pollinated varieties throughout the Corn Belt quickly disappeared and consequently uniformity in the cornfields greatly increased.

This increased the potential for genetic vulnerability e.g., Southern Corn Leaf Blight, a fungal disease, in 1970

© T. M. Whitmore

The shift to hybrids II• Unforeseen consequences of this

technology… Farmers were “tied” to the seed

companies – costs went up but production went up faster!

• Current opposition to genetic engineering (the new hybrid technology) Potential risks of introducing genetically

engineered varieties to the environmentGreed of companies, etc

• There was a lot less opposition and little if any discussion about the potential risks for traditional hybrids

© T. M. Whitmore

New Maize hybrids• Newest push is for open pollinated maize

varieties with commercial hybrid-like good qualities

• Apomixis (recent patents of a kind of cloning): to produce corn, wheat, and other cereal grains able to reproduce by themselves (saved seed) without losing hybrid vigor, desirable agronomic traits, or useful disease- or insect-resistance.

© T. M. Whitmore

Maize Ecology• Grows in more eco-zones than any other major

crop• Needs sufficient water especially during a 1-

month period of tasseling If too dry => significantly lower yieldsAlso need rain in later period when grain is

fillingThus drought is a problem: not total annual rain

but need sufficient in these key growth periods• Traditional farmers plant multiple varieties with

different maturities (with different dates of tasseling) so if rains are inconsistent they get better yields – less risk than monocrop

© T. M. Whitmore

Maize Production• Produces more food per hectare and per

labor than any other grain2x the yield of wheat; 7 m calories/ha (~

rice); wheat 4m calories/ha; more efficient than most grains in

converting sunlight due to C4 pathwaymuch of the plant can be used: eg stalks

for fuel and fodder

• A greater weight of maize is produced each year than any other grain

© T. M. Whitmore

Maize Production II• In 2000, all maize in world = 140 m ha; 96 m

in 3rd world (thus 2/3 of all maize land is in developing world)But only 46% of total production is in 3rd

world since hybrid (yellow field) maize in 1st world is more productive

• Worldwide production was over 600 million metric tons in 2003World average yield = 4,255 kg per hectareAverage yield in the USA was 8,600 kg per

hectaresub-Saharan Africa average yield = 1,316

kg per hectare

© T. M. Whitmore

Maize Production IV•World maize production

USA 43%China 18%European Union 7%Brazil 6%Mexico 3% (only!)

•Maize consumption (by people directly)Note Sub-Saharan Africa!

© T. M. Whitmore

US Maize Uses• The “Corn Belt”• In North America, fields are often planted

in a two-crop rotation with a nitrogen-fixing crop, often soybeans

• USA production uses56% animal feed18% export (much for animal feed) 13% ethanol (alcohol for fuel)5% High Fructose Corn Syrup8% all other industrial and food usesonly 4% of corn grown in 1st world goes

to human food directly

© T. M. Whitmore

Maize Uses II• “Invisible” food uses

Production of corn sweeteners: corn syrup keeps foods moist and prevents them

from quickly spoiling. Less expensive than table sugar in

United States due to subsidizing corn syrup production while taxing sugar imports

High fructose corn syrup (HFCS) is a modified form of corn syrup that has an increased level of fructose. Most all soft drinks sold in USA

© T. M. Whitmore

Maize Uses III• Production of ethanol in USA

Ethanol, a type of alcohol, is mostly used as an additive in gasoline to increase the octane rating

• Increasingly as major fuel source: Argued to be “greener”E85 (85% ethanol/15% gasoline)flexible fuel vehiclesTax breaks

• Ethanol is a significant market for U.S. corn, consuming more than 1.2 billion bushels in 2004

From J.C. McCannMaize and Grace© Harvard University Press

© T. M. Whitmore

Maize as food• Tasty and edible in many stages of

development: immature as corn on the cob mature as dried and ground as grain

• NutritionProcess of soaking maize in water with lime

(from wood ash) to soften for grinding (using a metate y mano) - changes chemical composition (nixtamalization)

Makes some amino acids (needed to make protein) more available (especially lysine)

Increases availability of B vitamins especially niacin (cultures that rely on corn without this process suffer from nutrition deficiencies)

© T. M. Whitmore

© T. M. Whitmore