Transcript Starchy Staples - NIU Department of Biological Sciences

Starchy Staples
Outline
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Storage organs
Potato
sweet potato
Yam
cassava
• Chap 14
Underground Food Storage
• One successful plant strategy is to keep important
parts of the plant below the ground, safe from
most animals and weather, and send up disposable
stems for photosynthesis.
• Food reserves are needed to build the aerial parts
of the plant before photosynthesis can take over.
– Seeds have food stored in the endosperm or
cotyledons.
– Plants that reproduce vegetatively often store starch
in modified roots or stems below the ground.
• A common strategy: plants as biennials. This
means they have a 2 year life cycle. Carrots, for
example.
– First year: concentrate on vegetative growth,
– Winter: store the food they made underground
– Second year: send up a flower stalk to reproduce.
Types of Storage Organ
• Modified stems:
– Stolons (also called runners) are
aboveground horizontal stems that produce
new plantlets (stems and roots) are their
nodes. Examples: strawberry and
crabgrass.
– Rhizomes are horizontal stems that are
underground, often just below the surface.
Examples: ginger and iris
– Tubers are swollen tips of rhizome buds.
Examples: potatoes
More Storage Organs
• More modified stems:
– Bulbs are underground stems
surrounded by fleshy leaves
that hold the starch, protected
by a layer of papery leaves.
Examples: onions, tulips,
daffodils.
– Corms are underground
stems that store food in the
stem itself, not in modified
leaves (as bulbs do). Corms
are surrounded by protective
papery leaves. Examples:
crocus, gladiolus, taro.
Modified Roots
• Tuberous roots are modified fibrous roots
that hold food. Examples: tuberous
begonias, sweet potato.
• Taproots can be enlarged as food storage
organs. This often happens in biennial
plants, which store one years’ food
production belowground, then use it to
grow reproductive structures the next year.
Examples: carrot, turnip.
Potato
• Solanum tuberosum, the white potato, is a
member of the nightshade family (Solanaceae)
along with tomato, chile pepper, and tobacco.
• The potato is a New World crop, native to the
Andean highlands of Peru and Bolivia
– Potato cultivation was widespread in North
and South America before Columbus, with
lots of varieties.
– Today, almost all potatoes are descended
from a subspecies native to Chile.
• Potato is a tetraploid, the product of a cross
between two diploid (and much less productive)
species.
• Potatoes are eaten worldwide, and they are the
fourth biggest food source, after rice, wheat, and
corn.
Potato History
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The potato was the main food energy source for the
Inca Empire in Peru before Columbus.
– After harvesting, potatoes were exposed to the cold
night air to freeze, then mashed and dried (a low-tech
form of freeze-drying). This kept them edible for many
months.
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The Spanish introduced the potato to Europe, but it
was not immediately popular.
– Partly because it is in the same family (and looks a lot
like) deadly nightshade!
– Most parts of the potato plant, other than the tuber, are
poisonous
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Potato cultivation slowly spread across Europe. It had
two advantages:
– It grew well in cold conditions. The European climate
was undergoing the Little Ice Age between about 1600
and 1850, when average temperatures were lower than
before or after, resulting in many crop failures
– The tubers could be hidden underground, out of sight
from tax collectors and marauding soldiers.
Irish Potato Famine
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In the 1800’s, Ireland was ruled by England, with laws that
prevented Catholics (most of the Irish) from getting an education
or owning land. Most Irish people rented tiny plots of land from
landlords who lived in England. The standard of living was very
low, and tenants could be evicted at any time.
– Rent was paid by cultivating the best land with wheat and oats,
which were shipped to England
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– In contrast, the English people were rapidly becoming more
prosperous due to industrialization.
Potatoes produced sufficient calories that a family could live on 1
acre of land, with a milk cow or a pig. No other crop could
produce enough food in such a small space.
Potatoes are propagated vegetatively, by planting the “eyes” of
the tubers. This means that all potato plants in a field are
genetically identical.
The potato blight, a fungal-like protist called Phytophthora
infestans , appeared in 1845. It came from Mexico. There was
very little genetic variation among Irish potatoes, so nearly all got
infected. It was called “late blight” because it destroyed the crop
just before it could be harvested.
More Potato Famine
• The blight continued until about 1850
– Half the potato crop lost in 1845
– 3/4 of the crop lost in 1846
• Political ideology in England allowed
little aid to be sent to the starving Irish.
Also, they weren’t paying their rent, so
many were evicted.
• Many Irish died of starvation and
disease. The population of Ireland in
1911 was half that of 1850.
• Many emigrated to the US and
elsewhere. About 1/3 of all Americans
today have some Irish ancestors.
• The blight itself was stopped by the use
of new resistant strains of potato, and by
the development of an effective
fungicide.
Potato Cultivation
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Most potatoes are grown from the “eyes” (buds) of the tubers. This makes the offspring
clones, genetically identical to the parents.
– The lack of genetic variability in potatoes makes them susceptible to widespread
diseases.
– In contrast, most other plants are grown from seed, which results from sexual
reproduction. The genetic variability introduced by randomly combining traits from two
different parents means that there are usually some plants resistant to any disease.
“Seed potatoes” are cut pieces of the tubers, which will grow into whole plants. They are
tested and certified as disease free: many diseases are passed through the tubers
Potato breeders grow the seed and hybridize them to produce new varieties.
They like a cool climate, and tuber formation is inhibited at temperatures above 85oF. In the
US, most potatoes are grown in Idaho, eastern Washington and eastern Oregon.
Uses of Potatoes
• Most potatoes are eaten by people:
– Fresh potatoes are baked or boiled
– Cut up into french fries
– Sliced thin and baked to make potato
chips
• Some use as animal feed
• Potato starch is used in the food industry to
thicken soups and sauces, and in the
manufacture of paper.
Sweet Potato
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Despite the name, the sweet potato (Ipomoea batatas) is not
closely related to the familiar white potato. Sweet potatoes are
in the morning glory (Convolvulaceae) family.
– Yams are another, entirely different plant, native to Africa. Most of
what is marketed as “yams” in the US are really sweet potatoes that
have a darker orange color than other sweet potatoes.
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Sweet potatoes are native to the New World, probably
domesticated in the region between the Yucatan peninsula and
Venezuela.
– However, sweet potatoes are also found in Polynesia.
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Sweet potatoes grow in tropical and warm temperate conditions.
It needs significant rain, but can’t stand waterlogging: the tubers
rot.
– Mostly grown in southern states of the US: North Carolina and
Louisiana are the main producers
– Also heavy users: Papau New Guinea and New Zealand (Pacific
Ocean), and Rwanda, Burundi, Uganda (in Africa)
– Lots grown in China, mostly as animal feed
Spread of the Sweet Potato
• One big mystery about world history is why
the sweet potato plant was cultivated in both
South America and Polynesia before the
European invasion. Also, the two groups use
roughly the same word for it: the Peruvian
word is “kumar” and the Polynesian word is
“kumara”.
• Polynesia was settled from western Asia,
probably the Malay peninsula, starting about
2000 years ago.
– Easter Island, the easternmost pacific island,
was settled about 1500 years ago, roughly the
same time as Hawaii and New Zealand.
– These islands were probably the last places
settled by humans on Earth.
– All done using double-hulled canoes, with
very fine navigation skills., transmitted orally.
Map of the Pacific Ocean
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Possible Polynesian-South American Contact
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In addition to the common use and words for the sweet
potato, chickens were also (apparently) found in both
Polynesia and South America before Columbus. Also, there
are other common words.
– Genetic and archeological evidence is still equivocal.
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It’s a long way from Easter island to South America, but it
is not an impossible voyage for the Polynesians.
– Thor Heyerdahl, a Norwegian, thought that maybe South
Americans the Pacific to Polynesia on balsa wood rafts. He
built one, the Kon-Tiki, and sailed it to the island of Raroia in
1947, which took 101 days. He then wrote a book, which
became a best seller.
– But, his theory that Polynesia was settled from South America
isn’t viable in light of modern genetics and archeology.
– And, it’s also not proof that there ever was any contact
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It has been suggested that the stone gods on Easter Island
had seeds in their mouths when the space aliens brought
them to Earth. The gods then spat the seeds eastward to
South America, and westward to Polynesia.
– Most authorities think this theory is unlikely.
Yam
• There are several species of cultivated yam, in
the genus Dioscorea, which is part of the
larger yam family (Dioscoreaceae).
• They are found in humid tropical regions
throughout the world, and have domesticated
several times independently. In parts of
Africa they are a major staple crop.
• The plants are perennial vines, up to 40 feet
long.
– Propagated asexually, using pieces of tubers with
buds.
• The yams themselves are tubers, which range
in size from potato to up to 40 kg (88 lb) and
10 feet long. They can be deeply buried, so
harvest is a challenge.
• Mostly starch, with some protein and vitamins.
Yams and Hormones
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A number of important human hormones are steroids: they have
a characteristic 4 ring structure.
– Male and female sex hormones, stress hormones, ion
balance hormones
Yams produce a chemical compound that resembles steroid
hormones.
– Probably used to defend against animals: used as a fish
poison in some places.
– Taken as a contraceptive by natives in Brazil.
In the early 1950’s, the steroid hormone cortisone was first
isolated, from the adrenal glands of 2,200,000 pigs. Obviously
not cost-efective.
Starting with the compound from yams, cortisone could be
produced for $2 per gram, incredibly cheap.
– Also other steroids including female sex hormones that
went into birth control pills, and male sex hormones used
(illegally) for body building.
Nowadays, synthesis is done from simpler materials,
eliminating the need for yams.
Yams and Twins
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Among the Yoruba of Nigeria, the rate of twins is 5-10 times
higher than is common in the US. They also eat lots of yams
there. Maybe that’s why they produce so many twins.
However, this is just a correlation: twins and yams occur together
in one part of the world. Is it a cause-and-effect relationship?
– Maybe the twins are caused by some genetic factor among the
Yoruba.
– Maybe it’s something else they eat, or some other environmental
factor
– Maybe the high rate of twins isn’t even true
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Google shows lots of websites, but none of them has any
references to scientific literature.
– Scientific papers are peer-reviewed. This doesn’t guarantee their
accuracy, but at least someone with a skeptical eye had to agree that
the conclusions were supported by the data.
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My opinion: I think it is unlikely to be true. If it were true, other
yam-eating cultures would also have more twins, and probably
some birth control pills would affect twinning.
Cassava
• Also called manioc. Manihot esculenta, a member of the
spurge (Euphorbiaceae) family.
• Not common in the US, except as tapioca pudding, but
the fourth most important calorie source in the world
(after rice, wheat, and corn), primarily in the tropics.
• A New World crop, originating in Brazil. Spread by the
Portuguese to Africa and India, then later to Indonesia
and the rest of Asia.
• The plant is a perennial shrub, with tuberous roots.
• Propagation through stem cuttings, not the tuberous
roots.
– Also, it grows quite well from seed, meaning there will be
a lot of genetic variation.
• Grows well with seasonal rainfall: it can survive 6
months of drought.
• High in starch, low in protein: needs to be supplemented
to avoid protein deficiency disease.
Cassava Processing
• Cassava roots contain poisonous
compounds called cyanogenic glycosides.
When acted on by digestive enzymes, they
produce hydrogen cyanide, which is very
poisonous.
• In some varieties, the poison has been bred
out
• For most varieties, the roots need to be
processed by drying, soaking, boiling,
grating, or fermenting (depending on the
culture) before they can be safely eaten.
– South American method: grate the roots, soak
them in water, then strain them through a cloth.
This washes out most of the poison. Then, dry the
mash by roasting it.
• Once processed, cassava can be stored for
later use