Dioscorea
Dioscorea Cultivation (Yam Cultivation)
Introduction: Dioscorea, commonly known as
yam, is a tuber crop grown for its starchy
underground tubers. It belongs to the family
Dioscoreaceae and is native to Africa, Asia, and
tropical America. The most commonly cultivated
species include Dioscorea rotundata (white
yam), Dioscorea alata (water yam), Dioscorea
esculenta (lesser yam), and Dioscorea bulbifera
(aerial yam)
Economic Importance:
Yams are a staple food in many tropical regions and provide a
significant source of carbohydrates. They are also rich in vitamins,
particularly vitamin C, and have good storage potential. Yams can
be processed into flour, chips, and other food products.
Origin of Dioscorea (Yam):
Dioscorea, commonly referred to as yam, is believed to have
originated in several regions across the tropical and subtropical
world. Its primary centers of origin include:
West Africa: This region is considered the primary center of
diversity for Dioscorea rotundata (white yam) and Dioscorea
cayenensis (yellow yam). These are the most important cultivated
species and are staples in West African diets.
Southeast Asia and Oceania: Dioscorea alata (water yam) is native
to Southeast Asia and Oceania. It is one of the oldest domesticated
species and has been widely cultivated throughout Asia and the
Pacific Islands.
South and Central America: Some lesser-known species, such as
Dioscorea trifida (cush-cush yam), originated in tropical regions of
South and Central America.
Yam cultivation and consumption have a long history, with evidence
of its use dating back thousands of years. The crop was
domesticated independently in different regions, reflecting its
cultural and agricultural significance across the world.
Here is an illustration depicting the origin of Dioscorea (yam) across
its primary regions of cultivation, including West Africa, Southeast
Asia, and Central America, alongside the different species of
Dioscorea and their characteristics. This visualization highlights the
diverse tropical regions where yams are grown.
Botanical Name of Dioscorea
The botanical name of the yam plant is Dioscorea. There are many
species within this genus, each with its specific botanical name.
Some of the most common ones include:
Dioscorea rotundata – White yam
Dioscorea alata – Water yam or Greater yam
Dioscorea esculenta – Lesser yam
Dioscorea cayenensis – Yellow yam
Dioscorea opposita – Chinese yam
Each species has its own unique characteristics, but they all fall under the Dioscorea genus
Classification of Dioscorea
Dioscorea, commonly known as yams, is a genus of flowering plants with
many species cultivated for their starchy tubers. Here's the botanical
classification of Dioscorea:
1. Kingdom:
Plantae
This places yams within the plant kingdom, which includes all multicellular
organisms that produce their own food through photosynthesis.
2. Division (Phylum):
Angiosperms (Magnoliophyta)
Dioscorea is part of the division of flowering plants, characterized by having
seeds enclosed within a fruit.
3. Class:
Monocots (Liliopsida)
Monocots are flowering plants that typically have one cotyledon (seed leaf)
in their seeds. This class includes grasses, orchids, lilies, and palms.
4. Order:
Dioscoreales
This order includes a small group of tropical plants known for their climbing
vines and starchy tubers.
5. Family:
Dioscoreaceae
This family includes the true yams, consisting of over 600 species of
twining vines, which produce underground tubers.
6. Genus:
Dioscorea
This is the genus under which all yams fall. Dioscorea species vary in size
and habitat and are known for their tuberous roots, which are edible in
many species.
7. Species:
There are over 600 species within the Dioscorea genus. Some of the most
notable species include:
Dioscorea rotundata: White yam, commonly cultivated in Africa.
Dioscorea alata: Greater yam or water yam, found in Southeast Asia.
Dioscorea esculenta: Lesser yam, found in Southeast Asia and the Pacific.
Dioscorea cayenensis: Yellow yam, often grown in West Africa.
Dioscorea opposita (syn. D. batatas): Chinese yam, grown in East Asia.
Each species has unique growing conditions, uses, and culinary importance
depending on the region.
Climatic Requirements:
Temperature: Yams require a warm tropical climate, with temperatures
ranging from 25-30°C (77-86°F).
Rainfall: Yams grow well in areas with an annual rainfall of 1000-1500 mm.
Well-distributed rainfall during the growing season is crucial for good tuber
development.
Soil: They prefer well-drained, loamy soils rich in organic matter.
The pH should be between 5.5 and 6.5. Yams do not thrive in
waterlogged or heavy clay soils.
Sunlight: Full sunlight is essential for proper growth and
tuber formation
Propagation: Yams are generally propagated vegetatively using
seed yams (small tubers) or pieces of mature tubers called setts.
Setts should weigh between 150-300 grams and be treated with
fungicide to prevent rot before planting
Land Preparation:
Clearing: Clear the land of any previous vegetation or weeds.
Tillage: Plow and harrow the soil to a fine tilth to create a loose soil
structure, which is ideal for tuber formation.
Mounding or ridging: Yams are often planted on mounds or ridges
to promote good drainage and facilitate tuber expansion.
Planting:
Timing: In tropical regions, planting is done at the onset of the
rainy season. It is typically carried out between March and June,
depending on the local climate.
Spacing: The recommended spacing is 1 meter between rows and
1 meter between plants. For smaller varieties, the spacing can be
slightly reduced
Depth: Setts should be planted at a depth of 10-15 cm (4-6
inches).
Crop Management:
Staking: Yams are climbers, and most varieties need staking to
support vine growth. Staking improves exposure to sunlight, reduces
pest attacks, and increases yield.
Weeding: Regular weeding is necessary, especially during the early
stages of growth. Mulching can help reduce weed competition and
retain soil moisture.
Irrigation: In areas with irregular rainfall, supplemental irrigation is
necessary to ensure consistent moisture during tuber formation.
Fertilization: Organic manure or compost should be applied
during land preparation. A balanced fertilizer containing
nitrogen, phosphorus, and potassium (NPK) can be applied at
various stages of growth to enhance yield.
Pest and Disease Control:
Pests: The common pests include yam beetles, aphids, and nematodes.
Pesticides or natural pest management practices like crop rotation can help
control them.
Diseases: Yams are susceptible to fungal diseases such as anthracnose, tuber
rot, and leaf blight. Proper field hygiene, use of disease-resistant varieties, and
fungicide application help in disease control.
Harvesting:
Yams are usually ready for harvest 6-10 months after planting,
depending on the variety. When the leaves and vines start turning
yellow and drying out, it is a sign that the tubers are mature.
Harvesting should be done carefully using tools like spades or forks
to avoid damaging the tubers.
Post-Harvest Handling:
After harvesting, tubers should be cured by storing them in a well-ventilated area
for 7-14 days to allow the skin to toughen and reduce water loss. This also helps
heal minor wounds and prolongs storage life.
Proper storage conditions (cool, dry, and dark) are important to prevent tuber
spoilage.
