|Traditional Storage of Yams and Cassave and its Improvement (GTZ)|
Yams are widespread in the humid tropics throughout the world and in a wide variety of species. Of particular significance are the white Guinea yam (Dioscorea rotundata Poir), the water yam Dioscorea alata L.), the yellow yam Dioscorea cayenensis Lam.) and the Chinese yam Dioscorea esculenta (Lour.) Burk.)
The white yam originates in West Africa, however, without a wild variety being known of it is the most important variety of yam cultivated for human nutrition not only in this region, but throughout the world.
Most widespread, but not of the greatest economic status, is the water yam. This variety is native to South East Asia and probably originates in Burma, today's Myanmar. The water yam, with the white yam, is the most important variety of yam cultivated in West Africa today.
The appearance of the yellow yam is very similar to that of the white yam Many authors also speak of a subspecies here (ONWUEME, 1978). Apart from some morphological differences, the yellow yam has a longer period of vegetation and shorter dormancy than the white yam. The yellow yam is native to West Africa where wild varieties also exist. Apart from the region of its origin, the yellow yam is only found with economic significance in the West Indies.
The Chinese yam comes from lndo-China. Nowadays it is most widespread in South East Asia, in the South Pacific and in the West Indies The Chinese yam has only recently been introduced to Africa and has only played a subordinate role here so far
The bitter yam (Dioscorea dumetorum (Kunth) Pax) is marked by the bitter flavour of its tubers. Some sorts are highly poisonous. The cultivation of the bitter yam is mainly limited to the West African region where wild varieties cam be encountered
There are many other varieties of yam, some of these are only of regional significance and do not occur in West Africa For this reason, a more detailed description of these can be dispensed with here.