Jimma University

College of Agriculture and Veterinary

Medicine

School of Graduate Studies

Department of Horticulture

A Lecture Note on Root and Tuber Crops

Production and Management

o Cassava = Manihot esculenta

o Sweet Potato = Ipomoea batatas

o Enset = Ensete ventricosum

o Tannia and Taro = Colocasia and Xanthosoma (Cocoyams)

o Yam = Dioscorea spp

Table of contents

Content page

General Overview of Root and Tuber Crops.................................................................................. 1 Similarities and Dissimilarities between Root and Tuber Crops.................................................... 2 Similarities between Root and Tuber Crops................................................................................... 2

1. Harvested Product Perishability.............................................................................................. 3 2. Consequences of Vegetative Propagation............................................................................... 3 3. Complications for Genetic Resource Conservation................................................................ 3 4. Labor for Production and Marketing...................................................................................... 4 5. Marketing from a Farm Perspective....................................................................................... 4 6. Technologies Yet-to-be-Developed........................................................................................ 4

Dissimilarities between Root and Tuber crops ............................................................................... 5 1. Genetic Systems...................................................................................................................... 5 2. Strategies for Genetic Improvement....................................................................................... 5 3. Farming Systems Perspectives................................................................................................ 6 4. Pest and Pathogen Systems..................................................................................................... 6 5. Off-farm Marketing................................................................................................................ 6 6. Starch Properties..................................................................................................................... 7

Cassava= Manihot esculenta........................................................................................................... 7 Sweet potato = Ipomea batatas..................................................................................................... 13

Cultivation ............................................................................................................................... 16 Enset = Ensete ventricosum (Welw.) Cheesman.......................................................................... 18 Colocasia and Xanthosoma (Cocoyams)...................................................................................... 22 Yams (Diocorea Spp).................................................................................................................... 26

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General Overview of Root and Tuber Crops

Root and tuber crops provide a substantial part of the world's food supply, and are also an

important source of animal feed and industrial products. On a global basis, approximately 45%

of root and tuber crop production is consumed as food, with the remainder used as animal feed or

for industrial processing for products such as starch, distilled spirits, and a range of minor

products.

The pattern of root and tuber crop utilization varies considerably among countries. In the

developing countries (with the exception of China and Brazil), relatively small amounts (less

than 20%) are fed to livestock. Most of the remainder is used locally as food. The relatively high

cost of transportation, processing, and storage, as well as the considerable time needed in food

preparation, frequently makes unprocessed root and tuber crops less attractive to urban

consumers.

The consumption of root and tuber crops as food in developed countries is considerably smaller

than it is in developing countries, but their use as animal feeds is relatively higher. A very small

proportion of root and tuber crop production (approximately 5%) is traded internationally. More

than two-thirds of those exports come from developing countries, with Thailand's cassava

exports accounting for more than half of the total. Apart from cassava, only potatoes are traded

internationally in significant quantities - mainly among developed countries.

There are considerable differences in the agro-climatic conditions suitable for the production for

the different root and tuber crops. Cassava is grown across a broad range of agro-climatic

conditions from sea level to 1,800 meters, and from areas with as little as 500 mm of rainfall, to

tropical rain forest areas with more than 2,000 mm per year. Potatoes, on the other hand, are

considered to be a high latitude/altitude crop, originating in the Andes, but now grown in a range

of environmental conditions, from traditional ranges to warmer, drier areas, including irrigated

production in Latin America, Asia, and portions of Africa.

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Sweet potato is understood to have originated in the Americas (as did cassava and potato), and it

too is grown over a considerable range of latitude and elevation (up to 2,500 meters).

Conversely, yams have a relatively narrower range of production, being mainly confined to the

tropical region throughout the world from sea level to 1,400 meters. The main production of yam

is in the savannah region of West Africa, where more than 90% of the crop is grown. Unlike

cassava, potato, and sweet potato, the white and yellow yam (Dioscorea rotundata and D.

cayenensis [esculenta], respectively) are thought to be indigenous to West Africa, whereas the

water yam (D. alata) is thought to have originated in Southeast Asia.

Most of the cultivated edible aroids are well adapted to high rainfall (and occasional flooding)

and can be cultivated in temperatures ranging between 16° and 30° C, at elevations up to 1,600

meters.

Similarities and Dissimilarities between Root and Tuber Crops

Root and tuber crops share some common similarities, based on their biology and agricultural

production and used. However, they also have a number of dissimilarities that are not

immediately evident to those not directly involved in research or the development of relevant

technologies.

Similarities between Root and Tuber Crops

The similarities of the root and tuber crops are:

o Perishability of the harvested product.

o Vegetative propagation and some related consequences.

o The need to conserve genetic resources, and some related complications.

o Labor demands for production and marketing.

o Marketing, from a farm perspective.

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1. Harvested Product Perishability

The perishability of the harvested products of root and tuber crops (i.e., high water content) is a

fundamental consideration that leads to a rationale for greater investments in post-harvest

technology research. There is a need for technologies that will allow either extended storage or

the processing of the harvested products to avoid otherwise enormous losses that can occur with

these commodities. The distinct advantage of grain crops is their "storage ability" and their

"transportability". Root and tuber crops, in much of the developing world, need to be consumed

at or near the point of production.

Cassava and sweet potato can be "field stored" in the ground for a few months with minimal loss

of quality if conditions are right. All of the root and tuber crops have the distinct disadvantage,

following harvest, of limited storability, and are fairly perishable if the conditions are not

suitable. This characteristic of root and tuber crops predetermines the need for post-harvest

treatment of these crops to preclude very large post-harvest losses.

2. Consequences of Vegetative Propagation

Another similarity of root and tuber crops is the common practice of vegetative propagation.

Relative to grain crops, root and tuber crops require sophisticated technologies for their

propagation. Moreover, vegetative propagation of crops increases the likelihood of transmitting

many different plant pathogens. In most developed countries, this type of need is dealt with

through institutional outreach programs (a.k.a. Cooperative Extension in the U.S.A.). But this

solution is very costly. The expense of this type of a technology transfer system seems beyond

the financial reach of many developing nations.

3. Complications for Genetic Resource Conservation

Another similarity of root and tuber crops relates to specific requirements for the conservation of

genetic resources. The requirement to propagate vegetatively and the perishability of the

vegetative organs means that root and tuber crops require substantially more resources to assure

adequate reserves are 'banked' for future generations. For some of the root and tuber crops true

seed can be substituted for vegetative materials, but this approach usually compromises the

genetic integrity of the collections.

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For each of the individual root and tuber crops a complementary approach to their genetic

conservation will need to involve a mix of different methods (primarily ex situ), as appropriate.

This would include field gene banks, in vitro conservation, and seed and pollen storage, along

with the storage of vegetative materials.

In situ conservation, (e.g., on farm gene banks) has some limited applications for root and tuber

crops. Field gene-bank conservation is costly and carries the risk of loss of the collection, when

in some situations, proper safeguards cannot be provided. Moreover, the requirements,

particularly for the latter approach and with in vitro conservation, vary significantly from crop to

crop. These issues are sometimes not accommodated during the allocation of resources for this

important area of science enablement.

4. Labor for Production and Marketing

The production, harvest and marketing of root and tuber crops are generally labor intensive. The

sheer bulk of root and tuber crops, compared to cereals is an even bigger problem than is their

underground harvest. Root and tuber crops can be harvested by means other than simply digging

up individual plants (e.g., ploughs, spinners, mechanical harvesters) but the volume to be dealt

with (stored or transported) remains a significant labor problem. The processing of traditional

consumable products from these crops may also require high labor inputs. In many countries,

women are heavily involved in each of these tasks, and thus the role of women is worthy of

special attention.

5. Marketing from a Farm Perspective

Root and tuber crops share some similarities from a market perspective at the farm level. For

instance, much of root and tuber crop production is consumed on-the-farm, or at distances that

are relatively close to production. In these situations the similarities of the various root and tuber

crops could be considered as one category, for research purposed. But the similarities of

marketing characteristics for root and tuber crops become quite dissimilar when considered from

an off-the-farm marketing perspective.

6. Technologies Yet-to-be-Developed

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Finally, one of the greatest similarities among root and tuber crops is unrealized yield potential

that could be attained through yet-to-be-developed technologies. The standing panel chose not to

use the term "yield gap" for this concept, as "yield gap" has been used to describe crop

production levels that could be increased using known technology. In the case of root and tuber

crops, the potential for yield is considerably higher than the actual yield, in most settings. All too

frequently, this is because the needed technology is not available to deal with yield-limiting

factors (water, nutrients) and yield-reducing factors (disease, pests). As a consequence, increases

in farmer yields is expected to be much greater than from attempts to increase the physiological

yield potential of crops already trapped on a yield plateau.

Dissimilarities between Root and Tuber crops

There are, however, in addition to the similarities noted above, some dissimilarities that

distinguish the individual root and tuber crops. These dissimilarities are: Genetic Systems of the

Individual Crops, Strategies for Genetic Improvement, Farming Systems Perspectives, Pest and

Pathogen Systems, Off-Farm Markets and Starch Properties.

1. Genetic Systems

To scientists familiar with the biology of the root and tuber crops, the genetics of these crops are

enormously dissimilar, as are the pests and pathogens that attack them and reduce yields. From a

superficial inspection, it is true that the breeding of root and tuber crops is primarily done

sexually, and that there are viruses, bacteria, fungi, insects, and mites that attack these crops to

varying degrees. The reality is that each of the pollinating systems and different ploidy levels

brings with it breeding complications, along with specific opportunities for genetic development.

2. Strategies for Genetic Improvement

Strategies for the genetic improvement of root and tuber crops differ significantly, since they

must to take into account the various production systems and end-uses. Some crops (e.g., sweet

potato, potato) may benefit from breeding cultivars adapted to shorter growing seasons, while

other crops (e.g., cassava) may need to fit into different and contrasting growing cycles. Other

considerations (e.g., crop and soil management practices, crop rotation schemes, rainfall

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patterns) mandate that decision making be done in the individual breeding programs. The needs

for improvement are usually unique to the crop, rather than to the group of crops classified as

root and tuber.

3. Farming Systems Perspectives

There are significant differences in the farming systems perspectives of root and tuber crops,

ranging from contrasting systems of production for some crops, to complex systems of

intercropping involving two or more root and tuber crops. All of these aspects are important

considerations, in as much as the transfer of know-how from one crop's farming system to

another is difficult, if not impossible. This means that most farming systems research must be

done for each root and tuber crop, thereby giving the appearance, falsely, of duplication of effort.

4. Pest and Pathogen Systems

The pest and pathogen complexes of root and tuber crops are remarkably dissimilar, in that none

of the viruses of one root or tuber crop can attack another. Knowledge of one pest or pathogen

may be generally applicable to other situations in other root and tuber crops, but the specific

information cannot be directly applied. This is an important consideration, in that the transfer of

developed technology is just as difficult from cassava to potato as it is from sweet potato to

wheat.

5. Off-farm Marketing

Root and tuber crops produced for off-farm markets can have considerable dissimilarities in

transportation, storage, processing, consumption, economics, consumer demand, and other

factors. These differences need to be taken into account when inter-Centre opportunities are

assessed for improving root and tuber crops, and for distinguishing among strategies for their

improvement vis-à-vis/ face-to-face with/ the mission of the CG System. In fact, some individual

root and tuber crops are presently experiencing a segmentation of markets that will undoubtedly

require substantially different types of cultivars to meet divergent market needs. Some examples

of this phenomenon are the emerging uses of cassava as an industrial raw material, as compared

with its traditional uses as a food. Similar differentiation is occurring with potato and sweet

potato.

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6. Starch Properties

Another dissimilarity of root and tuber crops is the properties of the starches that are produced in

the harvested roots and tubers. There has been a limited amount of work on the characterization

of root and tuber crop starches (mostly for potato, and to a lesser extent for cassava and sweet

potato), but work to date has shown considerable variability within and between the crops

evaluated. However, the methods required to evaluate the quality characteristic and assess the

product potential are similar for any starch source. In addition, the required primary processing

technologies (flour/starch) are also similar for all root and tuber crops. This information gap

represents a whole new area of research that needs to be addressed if post-harvest technology of

root and tuber crops is to become a reality.

Cassava= Manihot esculenta

Cassava or manioc is a woody shrub of the

Euphorbiaceae (spurge family) native to South America

and the Caribbean that is extensively cultivated as an

annual crop in tropical and subtropical regions for its

edible starchy tuberous root, a major source of

carbohydrates.

Cassava is the third largest source of carbohydrates for human food in the world, with Africa its

largest center of production. The flour made of the roots is called tapioca. Cassava is classified as

"sweet" or "bitter" depending on the level of toxic cyanogenic glucosides. Improper preparation

of bitter cassava leads to a large number of cases of a disease called konzo. Nevertheless, farmers

often prefer the bitter varieties because they deter pests, animals, and thieves.

Description

Unprocessed cassava root

The cassava root is long and tapered, with a firm homogeneous flesh enclosed in a detachable

rind, about 1 mm thick, rough and brown on the outside. Commercial varieties can be 5 - 10 cm

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in diameter at the top, and 50 - 80 cm long. A woody cordon runs along the root's axis. The flesh

can be chalk-white or yellowish. Cassava roots are very rich in starch, and contain significant

amounts of Ca (50 mg/100g), P (40 mg/100g) and vitamin C (25 mg/100g). However, they are

poor in protein and other nutrients. In contrast, cassava leaves are a good source of protein if

supplemented with the amino acid methionine despite containing cyanide.

Adaptability

Crops such as yam, maize, banana and plantain, cowpea or sorghum and millet are eco-

regionally specific; where as cassava is probably the only crop whose production cuts across all

ecological zones.

Economic impact

World production of cassava root was estimated to be 184 million tonnes in 2002, the majority of

production is in Africa where 99.1 million tonnes were grown, 51.5 million tonnes were grown

in Asia and 33.2 million tonnes in Latin America and the Caribbean. Nigeria is the world's

largest producer of cassava. However, based on the statistics Thailand is the largest exporting

country of dried cassava with a total of 77% of world export in 2005. The second largest

exporting country is Vietnam, followed by Indonesia and Costa Rica.

Cassava, together with yams and sweet potatoes are important sources of food in the tropics. The

cassava plant gives the highest yield of food energy per cultivated area per day among crop

plants, except possibly for sugarcane. Cassava plays a particularly important role in developing

countries’ farming - especially in sub-Saharan Africa -- because it does well on poor soils and

with low rainfall, and because it is a perennial that can be harvested as required. Its wide

harvesting window allows it to act as a famine reserve and is invaluable in managing labor

schedules. It also offers flexibility to resource-poor farmers because it serves as either

subsistence or a cash crop. Cassava is considered as Africa's Food Security Crop

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Uses

Human food

Cassava-based dishes are widely consumed wherever the plant is cultivated. Some of these

dishes have regional, national, or ethnic importance.

Bio-fuel

In many countries, significant research has begun to evaluate the use of cassava as an ethanol

bio-fuel. Under the Development Plan for Renewable Energy in the 11th Five-Year Plan in

China, the target is to increase the application of ethanol fuel by non-grain feedstock to 2 million

tonnes, and that of bio-diesel to 200 thousand tonnes by 2010. This will be equivalent to a

substitute of 10 million tonnes of petroleum. As a result, cassava (tapioca) chips have gradually

become a major source for ethanol production

Animal feed

Cassava is used worldwide for animal feed as well. Cassava hay is hay which is produced at a

young growth stage, 3–4 months and being harvested about 30-45 cm above ground, sun-dried

for 1–2 days until having final dry matter of at least 85%. The cassava hay contains high protein

content (20-27% Crude Protein) and condensed tannins (1.5-4% CP). It is used as a good

roughage source for dairy, beef, buffalo, goats, and sheep by either direct feeding or as a protein

source in the concentrate mixtures.

Ethno-medicine

The bitter variety of Manihot root is used to treat diarrhea and malaria. The leaves are used to

treat hypertension, headache, and pain. Cubans commonly use cassava to treat irritable bowel

syndrome, the paste is eaten in excess during treatment. As cassava is a gluten-free natural

starch, there have been increasing incidences of its appearance in Western cuisine as a wheat

alternative for sufferers of coeliac disease.

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Environmental conditions for cassava growth

• It does best in warm, moist climate 25-29oC

• It does very poorly under cold climate below 10oC

• Rainfall 1000-1500mm per year

• It is well adapted under conditions of drought 500mm per year

Cassava is a valuable crop

• Low moisture growth will cease and the plant shades some of its old leaves

• When moisture is again available the plant will resume growth and will produce new

leaves

• It is only during the first few weeks after planting the cassava plant can not tolerate

drought

Land preparation for cassava

• Most common are planting on unploughed land

• Planting on mound

Method of planting

• Inserting the cutting vertically

• Planting horizontally

• Planting at an angle

Planting Material

• Length of cutting

• Age of cutting

• Selection and handling of cutting

• Orientation of the cutting

Time of planting

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Field Operations

• Weed Control

• Fertilization

• Harvesting

Harvesting

Cassava is harvested by hand by raising the lower part of stem and pulling the roots out of the

ground, then removing them from the base of the plant. The upper parts of the stems with the

leaves are plucked off /pick off before harvest. Cassava is propagated by cutting the stem into

sections of approximately 15 cm, these being planted prior to the wet season.

Postharvest handling and storage

Cassava undergoes postharvest physiological deterioration, or PPD, once the tubers are separated

from the main plant. The tubers, when damaged, normally respond with a healing mechanism.

However, the same mechanism, which involves coumaric acids, initiates about 15 minutes after

damage, and fails to switch off in harvested tubers. It continues until the entire tuber is oxidized

and blackened within two to three days after harvest, rendering it unpalatable and useless.

PPD is one of the main obstacles currently preventing farmers from exporting cassavas abroad

and generating income. Cassava can be preserved in various ways such as coating in wax or

freezing.

The major cause of losses during cassava chip storage is infestation by insects. A wide range of

species that feed directly on the dried chips have been reported as the cause of weight loss in the

stored produce. Some loss assessment studies and estimations on dried cassava chips have been

carried out in different countries.

Yields

Factors Affecting Yield

� Cultivar used

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� Cultural operation � Fertilizer levels � Type of soil � Field spacing � Type of climate

Cassava pests

In Africa the cassava mealybug (Phenacoccus manihoti) and cassava green mite (Mononychellus

tanajoa) can cause up to 80% crop loss, which is extremely detrimental to the production of

subsistence farmers. These pests were rampant in the 1970s and 1980s but were brought under

control following the establishment of the IITA . The Centre investigated biological control for

cassava pests; two South American natural enemies Apoanagyrus lopezi (a parasitoid wasp) and

(a predatory mite) were found to effectively control the cassava mealybug and the cassava green

mite respectively.

The cassava mosaic virus causes the leaves of the cassava plant to wither, limiting the growth of

the root. The virus is spread by the whitefly and by the transplanting of diseased plants into new

fields. Sometime in the late 1980s, a mutation occurred in Uganda that made the virus even more

harmful, causing the complete loss of leaves. This mutated virus has been spreading at a rate of

50 miles per year, and as of 2005 may be found throughout Uganda, Rwanda, Burundi, the

Democratic Republic of the Congo.

Cassava Diseases

• Virus Diseases • Bacterial Diseases • Fungal Diseases

The Future of Cassava

• Its easy cultivation • Propagation is by means of none edible stem portion • High yield per hectare • Cheaper source of food calories than most crops • Population increase

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Sweet potato = Ipomea batatas

History

Scientists believe that sweet potato was domesticated more than years ago. There is still much

debate as to just where in the Americas this took place South America or 5000 Central America

although recent evidence suggests that it was the latter.

Taxonomy

Despite its name, the sweet potato is not related to the potato. Potatoes are members of the

Solanaceae family, which also includes tomatoes, red peppers, and eggplant, while sweet

potatoes belong to the morning-glory family (Convolvulaceae). And unlike the potato which is a

tuber, or thickened stem the sweet potato is a storage root.

It is a dicotyledonous plant which belongs to the family Convolvulaceae. Amongst the

approximately 50 genera and more than 1000 species of this family, only I. batatas is a crop plant

whose large, starchy, sweet tasting tuberous roots are an important root vegetable (Purseglove,

1991; Woolfe, 1992). The young leaves and shoots are sometimes eaten as greens.

The genus Ipomoea that contains the sweet potato also includes several garden flowers called

morning glories, though that term is not usually extended to Ipomoea batatas. Some cultivars of

Ipomoea batatas are grown as ornamental plants.

The edible tuberous root is long and tapered, with a smooth skin whose color ranges between

red, purple, brown and white. Its flesh ranges from white through yellow, orange, and purple.

This plant is a herbaceous perennial vine, bearing alternate heart-shaped or palmately lobed

leaves and medium-sized sympetalous flowers. The edible tuberous root is long and tapered,

with a smooth skin whose color ranges between red, purple, brown and white. Its flesh ranges

from white through yellow, orange, and purple.

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Global production

Because of its versatility and adaptability, sweet potato ranks as the world’s seventh most

important food crop—after wheat, rice, maize, potato, barley, and cassava. More than 133

million tons are produced globally per year. Asia is the world’s largest sweet potato-producing

region, with 125 million tons of annual production. China—at 117 million tons—accounts for 90

percent of worldwide sweet potato production. Nearly half of the sweet potato produced in Asia

is used for animal feed, with the remainder primarily used for human consumption, either as

fresh or processed products.

In contrast, although African farmers produce only about 7 million tons of sweet potato annually,

most of the crop is cultivated for human consumption. African yields are quite low—about a

third of Asian yields—indicating huge potential for future growth.

Facts

Latin America, the original home of the sweet potato, produces 1.9 million tons of sweet potato

annually. Production in North America is about 600,000 tons. The only European country that

produces sizeable quantities of sweet potato is Portugal, at 23,000 tons.

Over 95 percent of the global sweet potato crop is produced in developing countries, where it is

the fifth most important food crop. Sweet potato is currently grown in more than 100 tropical

countries.

In the densely populated, semiarid plains of eastern Africa, sweet potato is called cilera abana,

"protector of the children." This title alludes to the vital role it fulfills in thousands of villages,

where people depend on the crop to combat hunger.

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Disaster relief

Sweet potato has a long history as a lifesaver. The Japanese used it when typhoons demolished

their rice fields. Sweet potato kept millions from starvation in famine-plagued China in the early

1960s, and in Uganda, where a virus ravaged cassava crops in the 1990s rural communities

depended on the sweet potato to keep hunger at bay.

Nutrition

Sweet potato is high in carbohydrates and vitamin A and can produce more edible energy per

hectare per day than wheat, rice or cassava. It has an abundance of uses ranging from

consumption of fresh roots or leaves to processing into animal feed, starch, flour, candy, and

alcohol.

Diseases

Bacterial diseases

o Bacterial stem and root rot Erwinia chrysanthemi

o Bacterial wilt Ralstonia solanacearum

Fungal diseases

o Alternaria leaf spot and stem blight Alternaria spp.

o Alternaria storage rot Alternaria spp.

Nematodes

o Burrowing Nematode Radopholus similis

Nutrition and health benefits

Besides simple starches, sweet potatoes are rich in complex carbohydrates, dietary fiber, beta

carotene (a vitamin A equivalent nutrient), vitamin C, and vitamin B6.

Sweet potato varieties with dark orange flesh have more beta carotene than those with light

colored flesh and their increased cultivation is being encouraged in Africa where Vitamin A

deficiency is a serious health problem.

Despite the name "sweet", it may be a beneficial food for diabetics, as preliminary studies on

animals have revealed that it helps to stabilize blood sugar levels and to lower insulin resistance.

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Uses

The roots are most frequently boiled, fried, or baked. They can also be processed to make starch

and a partial flour substitute. Industrial uses include the production of starch and industrial

alcohol.

Culinary uses

Although the leaves and shoots are also edible, the starchy tuberous roots are by far the most

important product. In some tropical areas, they are a staple food-crop.

Sun dried slices of storage roots and sun dried crushed storage roots are a staple food for people

in north-eastern Uganda.

Sun dried slices of storage roots are mainly for breakfast, eaten with peanut sauce. People

generally eat this food while they are drinking a cup of tea in the morning, around 10 am.

Sun dried crushed storage roots will be mixed with cassava flour and tamarind, to make food

called "atapa". People eat "atapa" with smoked fish cooked in peanut sauce or with dried cowpea

leaves cooked in peanut sauce.

Candied sweet potatoes

Baked sweet potatoes

Sweet potato fries or chips

Sweet potato pie

Non-culinary uses

In South America, the juice of red sweet potatoes is combined with lime juice to make a dye for

cloth. By varying the proportions of the juices, every shade from pink to purple to black can be

obtained.

All parts of the plant are used for animal fodder.

Several selections are cultivated in gardens as ornamental plants for their attractive foliage,

Taiwanese companies are making alcohol fuel from sweet potato.

Cultivation

The plant does not tolerate frost. It grows best at an average temperature of 24 °C (75 °F),

abundant sunshine and warm nights. Annual rainfalls of 750-1000 mm are considered most

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suitable, with a minimum of 500 mm in the growing season. The crop is sensitive to drought at

the tuber initiation stage 50–60 days after planting and is not tolerant to water-logging, as it may

cause tuber rots and reduce growth of storage roots if aeration is poor (Ahn, 1993).

Depending on the cultivar and conditions, tuberous roots mature in two to nine months. With

care, early-maturing cultivars can be grown as an annual summer crop in temperate areas, such

as the northern United States. Sweet potatoes rarely flower when the daylight is longer than 11

hours, as is normal outside of the tropics. They are mostly propagated by stem or root cuttings or

by adventitious roots called "slips" that grow out from the tuberous roots during storage. True

seeds are used for breeding only.

Under optimal conditions of 85 to 90 % relative humidity at 13 to 16 °C (55 to 61 °F), sweet

potatoes can keep for six months. Colder temperatures injure the roots.

They grow well in many farming conditions and have few natural enemies; pesticides are rarely

needed. Sweet potatoes are grown on a variety of soils, but well-drained light and medium

textured soils with a pH range of 4.5-7.0 are more favorable for the plant (Woolfe, 1992; Ahn,

1993). They can be grown in poor soils with little fertilizer. However, sweet potatoes are very

sensitive to aluminium toxicity and will die about 6 weeks after planting if lime is not applied at

planting in this type of soil (Woolfe, 1992). Because they are sown by vine cuttings rather than

seeds, sweet potatoes are relatively easy to plant. Because the rapidly growing vines shade out

weeds, little weeding is needed, and farmers can devote time to other crops. In the tropics the

crop can be maintained in the ground and harvested as needed for market or home consumption.

In temperate regions sweet potatoes are most often grown on larger farms and are harvested

before frosts set in.

China is the largest grower of sweet potatoes; providing about 80% of the world's supply, 130

million tons were produced in one year (in 1990; about half that of common potatoes).

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Enset = Ensete ventricosum (Welw.) Cheesman

Given the restricted geographic distribution of

domesticated enset agronomists and bio-

geographers have long considered the Ethiopian

highlands to be the primary center of origin for

enset agriculture. Anthropologists, archaeologists,

historians, and other scholars have also developed

theories that argue for the domestication of enset

in Ethiopia as early as 10,000 years ago.

Enset [Ensete ventricosum (Welw.) Cheesman] is a major multi-purpose crop in Ethiopia, which

has been identified as the center of origin and diversity of enset

Enset is a perennial monocarpic crop belonging to the Musaceae family. For thousands of years

it has been used as a food crop in Ethiopia where it was once domesticated. Enset is an important

co-staple crop for >20% of the Ethiopian population living in the southern and southwestern

parts of the country, including many ethnic groups

Enset (Ensete ventricosum) is the main crop of a sustainable indigenous Ethiopian system that

ensures food security in a country that is food deficient. Enset is produced primarily for the large

quantity of carbohydrate-rich food found in a pseudostem and an underground corm called

“Hamicho”

Environmental adaptation

Domesticated enset is planted at altitudes ranging from 1,200 to 3,100 meters. However, it grows

best at elevations between 2,000 and 2,750 meters. Most enset-growing areas receive annual

rainfall of about 1,100 to 1,500 millimeters, the average temperature of enset growing areas is

between 10 and 21 degrees centigrade, and the relative humidity is 63 to 80 percent.

Does enset affect the environment?

• Observations in areas that have been planted with enset for many years suggest that

native soils have been altered positively by the long-term application of manure.

• Enset's perennial canopy of leaves and the abundant accumulation of litter also reduce

soil erosion

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• Because enset production improves soils, particularly with adequate manure, many enset

fields have been in continuous production for decades, if not centuries. because of the

multiple roles that manure plays in improving soils biologically, chemically, and

physically

• What does the current situation looks like today.

Enset affects the physical environment around houses where it is most commonly grown. Enset

serves the same role as trees, providing people, other plants, and animals with protection from

wind and sun. Having a field that partially encompasses the homestead is considered

aesthetically desirable by enset-based societies; enset beautifies the Ethiopian landscape by its

thick, dark green foliage.

Enset also affect the macro-environment of an area, enset, with deep roots and leaf canopies of

long duration; improve the hydrological dynamics of an area, As the proportion of enset

increases with respect to annual species, water infiltration increases and surface runoff decreases,

resulting in more water in the soil and aquifers. The result is increased water availability and

greater volume and duration of discharge to springs, decreasing the effective length of the dry

season.

The food uses of enset

The major foods obtained from enset are kocho, bulla and amicho. Kocho is the bulk of the

fermented starch obtained from the mixture of the decorticated (scraped) leaf sheaths and grated

corm. Although many different dishes are prepared from kocho, a pancake-like bread is the most

common

Bulla is obtained by:

1) Scraping the leaf sheath, peduncle, and grated corm into a pulp;

2) Squeezing liquid containing a starch from the pulp;

3) Allowing the resultant starch to concentrate into a white powder; and

4) Re-hydrating with water. It is considered the best quality enset food and is obtained

mainly from fully matured enset plants. Bulla can be prepared as a pancake, porridge, or

dumpling.

Amicho is the boiled enset corm, usually of a younger plant. Enset plants may be uprooted for

preparing meals quickly if the amount of enset harvested is insufficient, or for special occasions.

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The corm is boiled and consumed in a manner similar to preparation methods for other root and

tuber crops. Certain clones are selected for their amicho production.

Non-food uses of enset

Enset provides fiber as a byproduct of decorticating the leaf sheaths. Enset fiber has excellent

structure, and its strength is equivalent to the fiber of abaca, a world-class fiber crop. About 600

tons of enset fiber per year are sent to factories. The fiber is used to make sacks, bags, ropes,

cordage, mats, construction materials (such as tying materials that can be used in place of nails),

and sieves.

Fresh enset leaves are used as bread and food wrappers, serving plates, and pit liners to store

kocho for fermentation and future use. During enset harvesting enset leaves are used to line the

ground where processing and fermentation take place.

Particular clones (or varieties) and parts of enset plants are used medicinally for both humans

and livestock to cure bone fractures, broken bones, childbirth problems (i.e., assisting to

discharge the placenta), diarrhea, and birth control (as an abortifacieant).

Enset propagation

Suckers are usually produced from the two- to three year-old corms (10 to 20 centimeters in

diameter) and the true stem. These mother corm pieces are obtained by harvesting healthy plants,

cutting off the pseudo stems, removing the roots, and removing out the center or apical bud, once

the apical bud is removed, these lateral buds form suckers around the periphery of the mother

corm piece.

20 to 200 suckers will be obtained per corm piece. These suckers are usually allowed to grow for

one year before transplanting

Diseases of enset

Diseases are caused by bacteria, nematodes, fungi, and viruses. Bacterial wilt, caused by the

bacteria Xanthomonas campestris pv musacearum, is the most threatening to the enset system.

Bacterial wilt attacks plants at any stage, including full maturity.

Enset is attacked by numerous diseases in addition to bacterial wilt. These include enset corm

rot, enset sheath rot, as well as root-knot, lesions, nematodes, and virus diseases.

Harvesting and processing

The preferred harvesting time is before flowering. The time duration required to flowering time

depends upon climatic conditions, clone type, and management. Hence, the flowering time varies

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from 3 to 15 years but is optimally around 6 or 7 years. Enset processing is carried out by

women using traditional tools and the process is laborious, tiresome, and unhygienic.

How do enset-based farming systems contribute to food security in Ethiopia

Enset-based farming systems play an important role in food security in Ethiopia. The exact role

and value relative to other farming systems cannot be addressed without examining enset

production and consumption in relation to the concept of food security. Food security can be

explained in terms of:

1) Adequate availability of food in line with present population and demographic growth;

2) The nutritional adequacy of food intake;

3) Annual stability of the food supply;

4) Access to food (through production or the market) and

5) The sustainability of the food production capacity over the long term. Each of these five

features relating to food security is discussed briefly.

Some of the most dense rural populations of Ethiopia are located in regions practicing enset-

based farming in the southwestern highlands. Rahmato (1996) notes that; among the Wolayta as

landholding size declines, there is an increase in the cultivation of enset. These observations

indicate that the human carrying capacity (i.e., the number of people per unit of land area that

can be adequately fed by the food produced on the same land area) of enset and enset-based

farming systems is high and is likely greater than other crops and cropping systems for the same

agroecology and inputs.

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Colocasia and Xanthosoma (Cocoyams)

Kinds of Edible Aroids

The monocotyledonous Family Araceae (the aroids) contains several plants which are cultivated

and used for food in various parts of the tropics.

The most widely cultivated once are the following

A. Colocasia esculenta (taro, old cocoyam, eddoe, dasheen

B. Xanthosoma spp.(tannia, new cocoyam)

Classification of taro

Taro originated in south central Asia, probably in Malaysia. Apparently cultivation of taro as a

crop is also originated in this region. Numerous botanical varieties exist, but they fall generally

into two main groups:

• the eddo and

• the dasheen types

In the eddo types the corm is small and the cormels are large and in the dasheen type it is

opposite.

Classification of tannia Tannia originated in tropical America and was first brought under cultivation there. It is belongs

to the genus Xanthosoma, which is also a member of the family Araceae.

Major differences between tannia and taro

• The attachment of the petiole to the lamina is not at the edge of the lamina but in the

middle of the lamina on taro while the attachment of the petiole to the lamina is at the

edge of the lamina on tannia

• Tannia is more robust plant than taro

• The root system of tannia is like that of taro. The corm is more or less spherical and the

cormels are flask shaped and usually larger than those of taro

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Tannia Taro

Tannia

Tannia

Taro is a tropical plant grown primarily as a vegetable food for its edible corm, and secondarily

as a leaf vegetable. It is considered a staple in oceanic cultures. It is believed to be one of the

earliest cultivated plants. In its raw form the plant is toxic due to the presence of calcium oxalate,

although the toxin is destroyed by cooking or can be removed by steeping taro roots in cold

water overnight. Taro is closely related to Xanthosoma

Names and origin

Taro was probably first native to the lowland wetlands of Malaysia (taloes). Estimates are that

taro was in cultivation in wet tropical India before 5000 B.C., presumably coming from

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Malaysia, and from India further transported westward to ancient Egypt, where it was described

by Greek and Roman historians as an important crop.

Taro's scientific name is Colocasia esculenta (synonym C. antiquorum); esculent is an English

word taken directly from Latin and means edible. The Xanthosoma genus is closely related, and

several common names including cocoyam are used to refer to either Taro or domesticated

Xanthosoma species which share substantially the same uses. Taro may be distinguished as "taro

cocoyam" or "old cocoyam", with the term "new cocoyam" referring to species of Xanthosoma.

In Kenya, taro root is referred to as arrow root, in some Caribbean countries, it is sometimes

known as dasheen, the leaves are used to make a soup popular in the West Indies, called

callaloo soup. Taro is also known as dalo In the Fijian Islands and in Japan. Eddoe is another

name for taro.

Uses

The small round variety is peeled and boiled, sold either frozen, bagged in its own liquids, or

canned. The plant is actually inedible when raw because of needle-shaped raphides (calcium

oxalate) in the plant cells.

Typical of leaf vegetables, taro leaves are rich in vitamins and minerals. They are a good source

of thiamin, riboflavin, Fe, P, and Zn, and a very good source of vitamin B6, vitamin C, niacin, K,

Cu, and Mn. Taro corms are very high in starch, and are a good source of dietary fiber. Oxalic

acid may be present in the corm and especially in the leaf, and these foods should be eaten with

milk or other foods rich in calcium so as to remove the risks posed by ingesting the oxalate ion,

especially for people with kidney disorders, gout, or rheumatoid arthritis. Calcium reacts with the

oxalate to form calcium oxalate which is very insoluble, and is suspected to cause kidney stones.

Cultivation

Taro can be grown under flooded (lowland) or unflooded (upland) situations. Yields are

generally higher under flooded conditions, but the time required and the amount of effort

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expended in land preparation is greater. Tannia is grown almost exclusively under upland

conditions.

Planting Material

The commercial planting materials used for cocoyam production are:

a) Small corms or setts cut from large corms

b) Cormels or setts cut from large cormels

c) Stem cuttings consists of the apical portion of the corm and the lower 15-25 cm of the

petioles the later one the most preferred planting material.

Time of Planting

• In the tropics the major determinant of the time of planting for cocoyam is the availability

of moisture. Where there are distinct rainy and dry season, planting is done shortly after

the rains have become regular.

• Where irrigation facilities are available planting can be done any time.

Harvesting and Yield

• Cocoyams are ready for harvesting when most of the leaves begin to turn yellow.

Apparently, there are no morphological changes indicating maturity, but physiological

maturity corresponds to the time when sugars in the corms are at a minimum.

• The time from planting to harvesting varies with cultivars, regions as well as the method

of cultivation.

• Generally it is about 12 months for upland taro, and 15 months for flooded taro and 9-12

months for tannia.

Yield

• Yields of cocoyams vary greatly from place to place, depending on the conditions under

which they were produced, and the methods used for production. Taro average yield is

about 6 t/ha. For tannia average yields are 12-20t/ha.

26

Yams (Diocorea Spp)

Y A M

Botany Dioscorea is a large genus of over 600 species with subterranean tubers or rhizomes. The tubers

are storage organs and often grown to a considerable size; they produce short, fibrous roots and

annual shoots, which are twining (except in dwarf species), the direction of twining being

specific.

The genus Dioscorea is divided into a number of taxonomic sections; the important food yams

are grouped in the following: Enantiophyllum-D. alata, D. rotundata/D. cayenensis complex, D.

opposita and D. japonica; Lasiophyton-D. dumetorum and D. hispida; Combilium-D. esculenta;

Macrogynodium-D. trifida; Opsophyton-D. bulbifera. There are some 60 species that have been

used for food, but most are of little importance; the above (with the exception of D. japonica) are

described in the chapters following this general chapter.

Origin and distribution

The occurrence of Dioscorea spp. in southern Asia, Africa and South America long pre-dates

human history and domestication of the different species in these areas appears to have been by

aboriginal man. Wild yams and domesticated cultivars occur throughout the tropical and

subtropical world.

West Africa is the most important cultivation zone, where yam is a major staple, producing about

93 per cent of the world's edible yams, but the crop is also of considerable importance in parts of

eastern Africa, the Pacific area (including Japan), the Caribbean and tropical America.

Cultivation conditions

Temperature-most edible yams cannot withstand frost and make poor growth below 20°C.

Optimum growth occurs at about 30°C; temperatures much above this have an adverse effect,

especially if associated with drought. An exception is D. opposita (see Chinese yam).

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Rainfall-although generally considered drought resistant, yams require adequate moisture

throughout their growing period and there is a positive correlation between high and regular

rainfall, vine growth and tuber yield. For optimum yields adequate moisture between the 14th

and 20th weeks of growth is of great importance. The major areas of production are centered

where there is a sharply demarcated dry season of 2-5 months and a rainfall of 120-150 cm or

more during the growing season. In parts of West Africa yams are grown where the rainfall is as

low as 60 cm per year, but yields are very poor, while crops are also obtained where the annual

rainfall reaches 300 cm.

Soil-good drainage is essential and for optimum yields a deep well-drained sandy loam is

required. On heavy, waterlogged soils the tubers are liable to rot, while on poor soils the weak

root system is unable to obtain sufficient water or nutrients to produce reasonably-sized tubers.

Most yams are grown on land after it has been cleared from bush.

Planting procedure

Material-edible yams are normally propagated by the use of small tubers (seed yams), cuttings

off the tubers, setts (pre-sprouted tubers or pieces of tuber), or bulbils. It is possible to use vine

cuttings, but tuber production by this method is generally uneconomic. The best planting

material is the small whole tuber.

Species such as D. esculenta and D. trifida, which produce a fairly large number of tubers, can be

propagated very easily by reserving a few of the tubers and planting these at the beginning of the

next season. Other species such as D. bulbifera and some forms of D. alata produce aerial

bulbils, which can be used, but the majority of the more important food yams only produce 1-3

tubers a season and in this case setts cut from the tuber are often used and are referred to as tops

or 'heads' (proximal), middles, and bottoms or 'tails' (distal). In general, tops are preferred and

the larger the sets, the earlier and greater is the rate of germination

A recent development has been the production in Barbados of virus-tested planting material, in

which yams grown from virus-free meristem tip cultures are being multiplied in the field and,

after inspection, distributed for planting. This material has been tested in a number of Caribbean

islands and has given approximately double the yield obtained when conventional seed yams are

planted, and the operation is now commercial.

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Time of planting-yams

Time of planting-yams are not normally grown under irrigation and in areas where the rains last

8-10 months planting normally takes place just before or at the beginning of the rains. Where the

rainy season is less than 8 months it has been found that early planting, up to 3 months before the

rains, can give a 30 per cent increase in yield.

Seed rate-the number of setts used obviously varies according to the species and the cultivar, but

for most large-tubered yams 10 000-15 000/ha are used, requiring at least 2.5 t/ha of setts.

Growth period

Most edible yams normally reach maturity 8-11 months after planting, though in certain species

a first harvest may be obtained after 5 months. The growth period usually comes to an end at, or

shortly after, the end of the rainy season: neither late planting nor subsequent irrigation will

prolong growth beyond the normal annual periodicity for the particular species

Harvesting and handling

Harvesting and handling at the start of the dry season yam plants normally die back and the

tubers are ready for harvesting, though in most cases they may be left in the ground for several

weeks as deterioration is usually not rapid. In some species, example D. rotundata and D. alata,

an early crop may be taken as well as the main harvest; in this case the tuber is carefully cut

below the head and removed, leaving the top to grow again and produce another tuber, or tubers.

Yield

Under optimal conditions yams are among the most efficient producers of human food: yields of

70 t/ha (D. esculenta) have been recorded from West Iran and 58 t/ha (D. alata) from St. Vincent.

Under normal farming conditions, however, yields are considerably lower, the normal range for

yams in pure stands being: West Africa 7.5-18 t/ha; South-East Asia 12.5-25 t/ha; the Caribbean

20-30 t/ha. These yields are gross, and because a substantial quantity is used for propagation, net

yields are generally about 2.5 t/ha less.

Main use

Yams are a staple carbohydrate food, commonly eaten as a vegetable, either boiled, baked or

fried. In West Africa a major proportion of the yam crop is eaten as 'fufu', a stiff, glutinous

dough.

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Subsidiary uses

Yams are sometimes dried and made into flour; this is often the case with damaged yams or with

yams that are surplus to requirements, essentially as a method of storage. In recent years there

have been attempts at more sophisticated processing for export, example fufu from Nigeria,

canned yams and yam soup from Puerto Rico, and yam flakes from Barbados. In general these

attempts have not been commercial successes, largely owing to the high cost of the raw material.

Secondary and waste products

Peelings and waste from yams are often used for feeding poultry and livestock. The possibility of

using yams for the production of starch or of alcohol has been considered, but not developed, as

there are many cheaper sources of both these products in the countries where yams are grown.

Production and trade

Production-despite the increasing consumption of introduced foods such as cassava and rice in

the main yam-consuming area of the world (West Africa), it appears that yam production is

remaining constant at about 20 million tonnes per year. Some 97 per cent of the world's

production is from Africa (over 90 per cent from West African countries).