Environmental Engineering Reference
In-Depth Information
from the other species by its pink or green angular, winged stem. This yam is very
popular among farmers owing to its long shelf life of over one year in some culti-
vars, the ease of cultivation, and the commercial value. Tuber cuttings from water
yams sprout easily; even the peel exhibits sprouting potential. In addition to the
tubers, some water yam varieties produce aerial bulbils that are also used as “seed”.
Different varieties vary in texture, taste, and keeping qualities; hence farmers
usually plant several varieties to cater for their needs. Up to 10 different varieties
may be grown by a single farmer.
Bush yam (D. praehensilis; Plate 9) and cultivated yam (D. rotundata)
The second most popular yam type in terms of frequency of occurrence is the
bush yam (wild progenitor of
D. rotundata
), locally known as
Kookooase
bayere
(Twi language) and cultivated white yam (
D. rotundata
). These are
grown under permanent trees, mainly cocoa, in the cocoa-growing areas,
hence the name. The bush yams have rounded stem with varying pigmenta-
tions and various levels of thorniness, often bearing cataphylls. Owing to their
occurrence under the canopy of tall trees, they are very vigorous climbers with
very long internodes. In the Krobo area, the
Newbouldia
sp., locally known
as
nyabatso
, with its deep, soft tap-root system and low canopy shade is com-
monly used as a live stake for the yams. The bush yam (
Kookooase bayere
)
derives its popularity from the ease of cultivation, and the fact that it can be
managed as a perennial. The tubers are frequently left in the ground and har-
vested piecemeal as needed. Tubers left unharvested in the mounds remain
palatable even after dormancy is broken, until leaves are fully developed. New
plants developed from such tubers produce multiple yields with time. Bush
yam tubers do not store well and must be consumed within a couple of weeks
after harvest. This makes them relatively unimportant commercially. The com-
parative advantage of bush yams is the ease of perenniation and, hence, its
food security value.
Between 78 and 92 per cent of farmers in southern Ghana cultivate four to 10
different varieties of bush yams.
Yellow yam (D. cayenensis)
Of the remaining four species, the yellow yam or
nkani
(Akan-Twi name) is the
most important. This species has a round, often smooth stem and produces a char-
acteristic yellow-pigmented tuber that is revered by members of the Akuapem
tribe. Unlike the trifoliate yam, the yellow yam tuber is not bitter and does not nor-
mally form tuber clusters. It is also easily distinguishable from the trifoliate yam
by its cordate leaves and glaborous stems. Four cultivars of yellow yams were
encountered in the southern Ghana demonstration sites.
