Environmental Engineering Reference
In-Depth Information
bush yams are regenerated from volunteer seeds and new volunteer plants are also
produced from bulbils of bulbil-bearing yams or from tuber pieces of yams that are
inadvertently left in the ground.
Many species- or type-specific cultural practices have been developed to opti-
mize the yields of the different yam types. For example, in the case of mounding,
both yam type and soil structure are considered. On deep, friable soils where
moisture is not limiting, bush yams are planted in planting holes without mound-
ing, or with small mounds. On less favourable soils larger mounds are used.
Yellow yams are typically grown in very large mounds.
Farmers have of their own volition developed various strategies for maintaining
the diversity of yams cultivated. Sometimes methods of farm management such as
the use of group labour (the Nnoboa system) expose farmers to the different vari-
eties grown by different farmers and permit the exchange of germplasm. Other
practices, such as exchange of planting material for farm labour, also help to dis-
seminate and thereby maintain yam diversity.
Despite the various strategies adopted by farmers for the maintenance of yam
diversity, erosion of diversity is still a major problem. Many factors contribute to
this. For instance, planting material distribution is not well organized. The bulk
of it is constituted of heirloom or other common varieties that are under total con-
trol of the farmers who replant and maintain them. As commonly occurs in many
asexually propagated plants when improperly handled, viruses and other disease
organisms accumulate in them, leading to a decline in performance with con-
comitant loss of planting material.
There is the need to assist farmers in the maintenance of clean planting material.
Research organizations may participate in the cleaning and maintenance of buffer
stocks of the heirloom varieties for replenishing farmers' stocks when necessary.
Also, the rich experience gained by the farmers in the cultivation of the vari-
ous yam types may be exploited for the maintenance of yam agrodiversity by
forging partnerships between farmers and scientific institutions engaged in
germplasm conservation to enhance in situ conservation. Such a practice is
already in existence between the PLEC farmers of southern Ghana and the Plant
Genetic Resources Centre of Ghana.
REFERENCES
Abbiw, D. K., Useful Plants of Ghana: West African Uses of Wild and Cultivated Plants ,
London: Intermediate Technology Publications, Kew: Royal Botanical Gardens, 1990.
Blay, E. T., “Diversity of yams in PLEC demonstration sites in Southern Ghana”, PLEC
News and Views , No. 20, 2002, pp. 25-35.
Degras, L., The Yam. A Tropical Root Crop , London and Basingstoke: Macmillan Press 1993.
Kranjac-Berisavljevic, G. and B. Z. Gandaa, “Sustaining diversity of yams in northern
Ghana”, PLEC News and Views , No. 20, 2002, pp. 36-43.
Irvine, F. R., West African Crops , London: Oxford University Press, 1979.
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