1 Potato and Tuber Crops

Lecture 16

DIOSCOREA CULTIVATION

Plants belonging to genus Dioscorea of family Discoreaceae under Monocotyledons

are commonly known as yams. Dioscorea alata (greater yam) and D. esculenta (lesser yam)
are main yams of India. Another species, D. routundata (white yam or African yam), which
is under extensive cultivation in Western Africa, recently introduced to India is becoming
popular. All species are typical tropical crops grown for carbohydrate rich underground
tubers. They form staple food in many parts of Western Africa. In D. alata, tubers are
peeled, cooked and sued as vegetable. D. esculenta is consumed after boiling and peeling.

Dioscorea Family (Dioscoreaceae): True Yams

Subterranean tuber of a true yam (Dioscorea sp.), the third most important tropical
root crop after cassava and sweet potatoes. The venation and shiny, heart-shaped leaves of
true yams are unmistakable compared to those of sweet potatoes and other root crops.

Botany

Yam tuber is neither a root structure nor a stem, but may have its origin as a
hypocotyl structure. Tuber grows from a small corm structure located at base of stem. In all
yams, tubers are renewed annually. Tubers may be single or two or three. D. esculenta
produces a large number of small and spindle shaped tubers. D. bulbfera and D.alata
produces a large number of small and spindle shaped tubers. D. bulbifera and D.alata
produce aerial bulbs called bulbils from axils of leaves. Whole tubers or pieces of tubers
with stem are used for planting in yams. Bulbils can also used for propagation. Stem is weak
and climbs on trees by twining. In D. rotundata stem remains erect upto one metre height.
Leaves are simple. All species are dioecious. Fruits are dehiscent tri-locular capsules. Seeds
are small and dispersed by wind. Even though all the species have seed dormancy for three
months, D. alata does not exhibit seed dormancy. In D. alata, majority of male clones are
tetraploids (2n = 40) and majority of females have higher ploidy level (2n=60 or 80).

Varieties

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Improved varieties developed at Central Tuber Crops Research Institute (CTCRI),

Sreekaryam, Thiruvananthapuram in Kerala are given below :

Greater yam

(Dioscorea alata)

(Hindi : Ratula) (2n = 20, 30, 40-80)

Sree Keerthi : Tubers are conical with brown skin and white flesh having 20-22% starch. It
yields 25-30 t/ha in 9-10 months.

Sree Roopa : Tubers are digitate in shape with black skin and white flesh. Productivity is 25-
30 t/ha in 9-10 months.

Sree Shilpa : Tubers are swollen, oval and smooth with black skin and white flesh. Yield is
28 t/ha in 8 months.

Indu is a high yielding (39.39 t/ha) variety developed by Kerala Agricultural

University. Tubers are digitate with brownish black skin and white to pale flesh.

White yam (D. rotundata)

Sree Subhra : Tubers are cylindrical with brown and partially hairy skin and white flesh.
Yield is 35-40 t/ha in 9-10 months.

Sree Priya : It produces 2-3 tubers having smooth surface and good cooking quality. Yield
is 35-40 t/ha in 9-10 months.

Sree Dhanya : This is a dwarf and bushy variety with spineless stem and tubers containing
23.3% starch.

Propagation and time of planting

• In greater yam and white yam, tuber pieces of 250-300 g size are used as planting
material.

• For this, tubers are cut longitudinally with a portion of stem end and allowed to dry
under partial shade after dipping in cow dung slurry.

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• Planting is usually done during March-April.

• Plough / dig land to a depth of 15-20 cm.

• Take pits of 45 cm3 at a distance of 1 m.

• Apply 1½ kg compost or well rotten cattle manure in the pit and full up to ¾ with top
soil.

• Plant tubers and mulch with dry leaves.

• Approximately 1800-2700 kg seed material is required to plant one hectare.

Manuring

Apply cattle manure or compost @ 10 t/ha as basal dressing before planting.

A fertilizer dose of 80 kg N, 60 kg P2O5 and 80 kg K2O per hectare in two split doses
is needed for yams.

Half dose of N, full dose of phosphorus and half dose of potash are to be applied
within a week after sprouting.

Remaining nitrogen and potash may be applied one month after the first application.

Top dressing of fertilizers should be followed by weeding and earthing up.

Inter-culture

Vines are allowed to trail on shrubs or trees or props for high productivity. Tubers are
harvested in 9-10 months when leaves turn yellow in colour. Harvesting is done by digging
surrounding, area and exposing tubers.

Lesser Yam (D. esculenta) (2n = 40, 60, 90, 100)

Hindi : (Suthni)

Sree Latha : Tubers are oblong to fusiform in shape with creamy white flesh and greyish
brown skin covered with thin hairs.

It yields 20-25 t/ha in 8-9 months.

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Tubers have 18.4% starch content.

Sree Kala : Tuber is sweet, round and smooth.

Yield is 20-25 t/ha in 8-9 months.

Cultivation of lesser yam is different from that of greater yam or white yam. Plough /
dig the land thoroughly and make small mounds at a distance of 70 cm after incorporating
compost or well rotten cow dung. Plant whole tubers of 100-150 g. Manuring and other
cultivation practices are similar to that of greater yam. Trailing is necessary to expose leaves
to sunlight. It is done within 15 days after sprouting by coir rope attached to artificial
supports in open area. Lesser yam is harvested in 8-9 months after planting. Harvesting is
done by digging out tubers carefully.

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