• Yam is a tropical tuber crop that is cultivated in Africa, Asia
and South America.
• After cassava, yam is the second most important tuber crop
• In West Africa,50 million tons are cultivated on about 4
million hectares annually, accounting for more than 90% of
the world’s production.
Origin and distribution
• Dioscorea rotundata was first domesticated in West Africa in
about 5000 BC.
• Three main centers of origin of yams have been identified:
Different species of the genus Dioscorea may have different
regions of origin.
Types of yam
White yam (D. rotundata) and yellow yam (Dioscorea
• These are native to Africa and are the most widely cultivated
types of yams in this region.
• They can grow large with vines reaching lengths of up to 12m.
• The tubers usually weigh between 2.5 and 5 kg each, but can
attain weights of as much as 25 kg.
Water yam (Dioscorea alata)
• Also called as ‘winged yam’ or ‘purple yam’
• It is perennial, vigorously twining vine with winged stems.
• The vines grow to 10m and are freely branching.
• The tubers are large with purple flesh.
• The plants normally grow for 8–10 months, and then go
dormant for 2–4 months.
• During dormancy the aerial stems die back.
Lesser yam (Dioscorea esculenta)
• It was one among the first yam species cultivated.
• It is native to Southeast Asia and is among the most
commonly cultivated species there.
• Its vines seldom grow longer than 3 m and the tubers are
• It is easily prepared and have good flavor.
• The small size of the tubers allows for mechanical
Air potato (Dioscorea bulbifera)
• It forms bulbils at the base of the leaves.
• The bulbils are more important food product compared with
• The name ‘air potato’ is derived from the size of the bulbils
equaling those of potatoes (0.5–2 kg).
• Air potato is hardly grown commercially.
• But, it is popular in home gardens as it starts yielding after 4
months and continues producing for the entire life of the vine
Chinese yam (Dioscorea opposita)
• As the name suggests, it is native to China
• The plant is smaller than the African yams.
• Its tolerance to frost enables cultivation in much cooler
• It is mostly being grown in China, Korea, and Japan.
• The tubers are harvested about 6 months after planting
Bitter yam (Dioscorea dumetorum)
• The cultivation of this species requires less labor
than other yams.
• Its wild forms may be highly toxic.
• They are used as bait and subsequently used to
• A high Yielding variety of Greater yam( Dioscorea alata ) with
large sized tubers, good cooking quality and excellent taste.
• It is a clonal selection from germplasm.
• They Climb to a height of 4-5 m.
• Starch content is 20-22 % on fresh weight basis and maturity
duration is 9-10 months.
• Average Yield is 25-30 T / Ha.
• They are suitable for intercropping with banana and can be
grown in mature coconut gardens.
• It is the first hybrid released in Dioscorea alata.
• Inter varietal hybrid between Da-140 & Sree Keerthi
• Tubers are medium sized, oval and has good cooking quality.
• It has cordate leaves with overlapping lobes, lamina slightly
cupping, and petiole purple at both ends.
• Swollen oval tubers with white flesh.
• Yield potential is 40 t/ ha. and average yield is 28 t/ ha.
• They are easily harvestable.
• It is a variety of Greater yam
( Dioscorea alata )
• Tubers are medium sized and
excellent cooking quality.
• It is also a clonal selection from
• Starch content 16-18 % and
protein 1-2 % on fresh weight
• Duration is 9-10 months and
average yield is 25-30 T / Ha.
• High yielding greater yam
• Tubers long, oval with
excellent cooking quality.
• Maturity period is 9 months
• Average yield is 30 T/Ha.
• A high yielding and widely adaptable variety of Lesser yam
(Dioscorea esculenta ).
• It is a selection from indigenous germplasm.
• They climb to a height of 2.5-3 m.
• Duration is 7.5- 8 months and average yield is 25 T/ Ha.
• Cooking quality fair, non bitter with good flavor and
• Starch content is 24.4 % and shelf life of tuber is 2-3
• Early maturing variety of lesser yam.
• It is a selection from exotic germplasm named Kombi.
• It matures in 7 months.
• oval tuber shape and has excellent culinary quality.
• Average yield is 20 T/Ha.
• A high Yielding variety of white yam ( Dioscorea rotundata)
• It is a seedling selection from the African variety Umidika
• Cylindrical tubers and excellent cooking quality.
• They are drought tolerant with novel flavored
• Suitable for intercropping in mature coconut gardens as well
as with banana.
• Starch content is 20 - 21 % and protein content is 2- 3 % on
fresh weight basis.
• Maturity duration is 9 - 10 months and average yield is 35 -
40 T / Ha.
• A high yielding variety of white yam (Dioscorea rotundata )
with cylindrical tubers.
• It is the first dwarf bushy variety and it does not require
• It is accommodated in closer spacing.
• Duration is 9 months. Average yield is 20 T / Ha.
• It is a selection from the African variety lwo.
• Tubers are brown skinned and partially hairy with cylindrical
• They are drought tolerant.
• Starch content is 21-23 % on fresh weight basis and average
yield 35-40 T / Ha.
• Duration is 9 - 10 months.
• It is a high yielder (35 / ha)
• Has good culinary and
• Tuber light purple flesh
• It is a greater yam variety
released for its high
yield(30 t /ha)
• Moderate tolerance to
• It is a clonal selection of
greater yam with long
• They have excellent
• They are field tolerant to
leaf spot, scales and mealy
• Avarage yield is 25 T/Ha.
• Released from KAU
• It is grown as pure crop as
well as intercrop.
• Suitable for the alluvial soil
• A popular product made from white and yellow yam named
‘Fufu,’‘Foutou,’ or ‘Iyan’ or ‘Pounded yam’ which is usually
eaten with different sauces and a source of animal protein.
• ‘Ube,’‘Ubi,’ or ‘Uhi is a product prepared from water yam
which is popular in west Africa.
• It contains abundant amounts of thiocyanate, which is an
agent counteracting sickle cell anemia in humans.
• Dioscorea batatas, a species cultivated in China (locally
called ‘Shanyao’) only for medicinal purposes are used in
• Dioscorea villosa, a species rich in diosgenin(steroid)which
is used in estrogen replacement therapy
• Yam tuber has its origin in a hypocotyl structure.
• Tuber grows from a small corm structure located at base of
• 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, Dioscorea alata does not exhibit seed dormancy.
• In Dioscorea alata, majority of male clones are tetraploids (2n
= 40) and majority of females have higher ploidy level(2n=60
• The climate of is of two wet seasons: the main wet
season begins in March and ends in July, and a shorter
one occurs in September and October.
• It is characterized by a mean air temperature of around
• a relative humidity of about 70%, and an annual rainfall
of 1000–1200 mm.
• Yam is grown in fertile forest soils and also cultivated
in sandier savannah types of soils.
• This is the most important method of propagation in the
• The planting material is called a ‘set’ and the size of each set
should be between 400 and 500 g.
• The sets are pregerminated in moist sawdust or coconut coir.
• There are three types of sets that can be obtained from whole
tuber– head sets ,middle sets, and tail sets.
• Head sets are the best to plant because of the presence of
eyes, which give rise to the new plants.
• Whole small tubers can also be planted.
• Minisets are small pieces of tubers of 25–50 g size that are
dipped into a fungicide/insecticide.
• The cut surfaces are then allowed to dry before planting to
produce seed yams (planting material)
• The miniset technique produces both healthy and high-
yielding planting material while reducing costs of seed yam
production and improving availability of planting material.
• Vine cuttings are another way to produce plants that form
healthy mini tubers to be used as seed material.
• 6- to 8-cm-long basal vine cuttings are dipped into a rooting
hormone and placed into a propagating bin.
• If successful, vine cuttings give a high multiplication rate
without the use of tubers,which can limit the costs for
• This method is still poorly adopted by farmers.
• However, with the expected simpliﬁcation of this
technology, farmers could apply it in order to produce
healthy seed tubers.
• When cultivating as monocrop, yam is planted with
a spacing of 50-100 cm X 100cm.
• In intercropping the distance between yam plants is
determined by the number and types of associated
• Yams are planted using four main methods, namely
• 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 .
• 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.
• At weekly intervals in the initial stage and later at about 10
• During rainy season no irrigation is needed.
• Intercropping with legumes like cowpea, horsegram, cluster
bean and French bean has been found to smother weeds.
• Provide an extra income without adversely affecting the
tuber yield and diosgenin content.
Staking of yam
• It is necessary to optimally expose the leaves to the sunlight
throughout its growth, especially in the climbing yam.
• The larger the surface area of the plant exposed to sunlight,
the higher are the yields that are obtained.
• Nonstaked cultivation is also practiced.
• It suppresses weeds better, but gives lower yields.
• Yam plants are usually staked soon after emergence.
• Different methods of staking include
(1) individual staking (one stake per plant)
(2) pyramidal staking (tops of several stakes
are slanted to form a peak),
(3) trellising (string wire between two strong
• Weed control is most important during the ﬁrst 12– 16
weeks after planting for seed yam i.e. until the yam foliage
will start covering the soil.
• The critical period for table yam is 4–16 weeks after
• Weeding is done 3–4 times during the season.
• Yield reduction of upto 90% due to heavy weed infestations
have been reported.
• Yams mature 7–9 months after planting, indicated by the
yellowing of the leaves and natural dieback of the vines.
• In order to maximize yield, harvesting must be done when
the yam reaches full maturity and before the soil becomes
• Yields about 20-25t/ha.
• yams with bruises must be cured, and dipped in wood ash, in
order to avoid fungal rot.
• Good storage is best achieved in shaded, cool conditions
(29–32⁰C) with relative humidity of 90–95%.
• Traditionally, yam is stored in barns of vertically arranged
wooden poles and palm leaf midribs.
Pest of yam
NEMATODES (Scutellonema bradys and Meloidogyne spp.)
• Early nematode attack endangers seedling emergence due to
rotting of the sets in the soil.
• Important preventive measures include proper clearance and
• Nematodes can be controlled by crop rotation.
• Staggered planting is also effective.
• Intercropping of Crotalaria spp. alone, or in combination
with pigeon pea(Cajanus cajan)has also shown to be an
effective control measure.
• Attack occurs just before harvest when the beetles feed
• The holes the beetles drill into the tubers reduce their market
• Incidences of yam beetle can be controlled by growing the
crop far away from water bodies.
• Spraying with botanicals such as neem preparations
• Mulching with Cymbopogon citrates and Ocimum viride
reported as effective control strategies.
MEALY BUGS (Planococcus dioscorea) and SCALE
INSECTS (Aspidiella hartii)
• Mealy bugs and scale insects form whitish colonies, which
may cover the entire tuber.
• The sucking insects cause a certain weight loss of the tuber.
• Infested tubers are not suitable for sale.
Diseases of yam
TUBER ROTS (Botryodiplodia theobromae, Rhizopus
nodosus, Fusarium oxysporum, Fusarium solani)
• Tuber rots mainly affect tubers of white yam, especially in
• Tubers having suffered damage to their epidermis must not
be stored in the same lot as unaffected tubers.
• yam sets may be dipped in ash solution and air-dried before
• Fungal incidences can also be controlled by a proper crop
YAM MOSAIC VIRUS
• Transmitted by aphids.
• Typical symptoms on yams include mosaic, shoestring,
green vein banding on leaves, and stunting.
• Effective preventive measures involve planting of resistant
varieties and the use of healthy planting material
• Anthracnose is a serious disease, which can have devastating
impacts in early stages.
• Attacks results in blackening between leaf veins and dieback
• The disease is favored by wet, humid, and warm weather
• It is most severe on white yam than on other edible yams.
• Anthracnose spreads by infected seed, rain splash, and moist
• Use of resistant variety is the best way to control.