Integrative Biology 363

ROOT CROPS



OUTLINE:
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CHAPTER 7 IN THE TEXT

Introduction
Root crops are underground parts of plants and include rhizomes, tubers, roots, stems, and leaves. Other than in the U.S., Western Europe and Japan, they are usually hand harvested.
Probably domesticated before seed crops. Used by most hunter-gatherer societies. Domestication has not affected many of them significantly. Usually larger size. Sometimes lower toxicity. Used in all cultures, but only major in a few: e.g., the potato in Europe, minor root crops in the Andes, and cassava in the lowland tropics.
About as much grown in terms of tonnage as cereal grains, but much less nutritional value.
The most important root crops are: Cassava, potato and sweet potato.
Crops from tubers and rhizomes.
Storage structures of plants. Often reproduced vegetatively. Mostly water. Some minerals and water. Starch. Used in most pre-agricultural cultures. Only in a few cultures have these become major food crops, mostly at high elevations in the tropics or in the wet lowland tropics.
Difficult to estimate production of many of these as they are consumed locally.
Mostly water and starch. Shipping involves shipment of water usually. Little protein or fats. Most of them spoil easily when harvested.

Potatoes
Potatoes (Solanum tuberosum, Solanaceae) and other related species were domesticated in Andean South America. Cultivated at least 4000 years ago. These will grow at elevations where few other crops will grow.
The early Spanish found them from Colombia to Chile. They are often preserved by freeze drying. They are made into chuño.
Either Sir Frances Drake or Sir Walter Raleigh brought back potatoes to England. The potato was enthusiastically received into Ireland. The climate was particularly suited to growing potatoes. By the 1840's the Irish ate unbelievable quantities of potatoes.
In 1845, the potato blight (Phytophthora infestans) struck and wiped out the potato crop. Perhaps 1-2 million people died. At least another million came to the U.S. People obviously began to realize the hazard of depending too heavily on one crop.
Today potatoes are grown everywhere in upland tropical and in temperate parts of the world. Reproduced vegetatively. Burbank produced many new lines. Seeds usually sterile. Solanum tuberosumcultivars are usually tetraploids.
In the U.S. most of crop goes into potato chips and instant mashed potatoes. They are freeze dried. Solves much of shipping weight problem.
Tuber about 80% water, about 20% starch, 2% protein.
Toxicity of potatoes. Lenape line of chipping potatoes. Greened tubers can produce teratogenicity. In some areas of Bolivia, people practice geophagy to absorb the toxic materials from primitive lines of cultivated potatoes.
Often treated to prevent sprouting. Harvested potatoes washed and stored cool. Sugar is converted to starch on storage.
Russia, Belarus, Ukraine, and Poland major producers. In the U.S., Florida and California (winter) and Maine, California, Idaho (summer). Newfoundland, maritime provinces, and Vancouver Island, B.C. in Canada.

Potatoes in a market

Sweet potatoes.
Sweet potatoes (Ipomoea batatas, Convolvulaceae) are native to northwestern South America. They were taken very early to the South Pacific area and many considered them native there. Others postulated that they were taken from South America to the South Pacific by pre-columbian voyagers. This partially inspired Kon Tiki.
They have been found in South America as far back as 8000-10000 years. They were cultivated by 2000 B.C. Some feel that they go back in the South Pacific as far as 1200 A.D.
A hexaploid. Wild forms not known with certainty. Origin complex.
The sweet potato is a true root. Also reproduced vegetatively using portions of the aerial stem. The roots contain about 2% protein. Lots of vitamin A. In Japan, (especially) sweet potatoes are a major crop. They are used there to prepare starch, wine and alcohol. They are also widely fed to animals. China is easily the world's leading producer. Widely eaten in the southern U.S. Not eaten particularly in Europe.

Sweet potatoes

Cassava or Manioc.
Cassava (also known as manioc or yuca) (Manihot esculenta) is widely eaten. It is the major starchy food for more than 500 million people. This plant is native to northern South America (probably) and has been cultivated for thousands of years.
Griddles for cooking it go back at least 2000 years. However, since the crop developed in the lowland tropics where preservation is poor, it may go back much farther. It contributes over 37% of the total calories consumed in Africa and 11% in Latin America. Little nutritional value other than starch. About 30% starch. Little protein. Doesn't keep well when harvested.
Toxic if not processed properly. The natives of South America had developed technology to remove the cyanide generating compounds. Sweet and bitter cultivars.
Highly productive and little labor involved. Will keep for several months if left in ground. Reproduced vegetatively from stem cuttings.
Sweet types often boiled and fried. Bitter types often made into "tortas" or "farinha". Tapioca made from partially gelatinized cassava starch.

Cassava in a market
Pressing cassava
Cooked cassava

Yams or Ñame
Not to be confused with the sweet potato (Convolvulaceae). Ignaime (French) or ñame (Spanish) ... but probably originally from an African language. These are Dioscoreaspecies and members of the Dioscoreaceae. Different species cultivated in Africa (where they were especially important), Asia, and the Americas. Probably tubers.
Reproduction asexual. Many poisonous and must be peeled and/or cooked to remove toxic principles. Yams relatively high in protein for root crops.
In most places where yams were formerly cultivated, they have been replaced by sweet potatoes or cassava.

Ñame, calabaza, yuca, ocumo blanco, and ocumo chino

Taro and its relatives.
These are plants of the Araceae. Taro is Colocasia esculenta. Members of this family domesticated as root crops in both the Old and New World. Colocasiais native to Asia.
A corm. About 30% starch, 3% sugar. Must be boiled to be eaten. A staple in the Polynesian area. In Hawaii, they use to make poi. Hawaiians used to eat 10-20 lbs. per day.

Taro in the field

Arrowroot
Used as a root crop, but usually cultivated today for the starch. Native to the New World. Member of the Marantaceae. Marantaspp.

Canna edulis
This plant is also native to the New World. Several species are cultivated for ornamentals, but one for the roots. Cultivated in many parts of the world today.

Minor Andean root crops.
A large number of these were domesticated in the Andes. Few (other than the potato) were used outside of the area.
añu = Tropaeolum tuberosum
arracacia = Arracacia xanthorrhiza
oca = Oxalis tuberosa
melloco = Ullucus tuberosus, Basellaceae, second only to potatoes in upland Peru.
maca = Lepidium meyenii, Brassicaceae or Cruciferae.
llacón = Polymnia sonchifolia, Asteraceae or Compositae.


Jerusalem artichokes


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Revised February 2005


© David S. Seigler, Integrative Biology 363, Plants and Their Uses, Department of Plant Biology, 265 Morrill Hall, 505 S. Goodwin Ave., University of Illinois, Urbana, Illinois 61801, USA. 217-333-7577. seigler@life.uiuc.edu.