Yam-Importance and production of yam
Yams are starchy staples in the form of large tubers produced by annual and perennial vines grown in Africa, the Americas, the Caribbean, South Pacific and Asia. There are hundreds of wild and domesticated Dioscorea species. White Guinea yam, D. rotundata, is the most important species especially in the dominant yam production zone in West and Central Africa. It is indigenous to West Africa, as is the Yellow yam, D. cayenensis. Water yam, D. alata, the second most cultivated species, originated from Asia and is the most widely distributed species in the world.
Consumer demand for yam is generally very high in this sub-region and yam cultivation is very profitable despite high production costs.
Yam production is declining in some traditional producing areas due to declining soil fertility, increasing pest pressures and the high cost of labor. Smallholders therefore need access to innovations to reduce labor and improve productivity.
Yams are grown by planting pieces of tuber, or small whole tubers (‘seed yams’) saved from the previous season. Small-scale farmers, the majority of producers, often intercrop yams with cereals and vegetables.
The major pests that affect yams include insects such as leaf and tuber beetles, mealy bugs, and scales; parasitic nematodes; fungi causing anthracnose, leaf spot, leaf blight, and tuber rot; and viruses, especially the yam mosaic virus (YMV).
In West and Central Africa tubers are planted between February and April, depending on whether in humid forest or on the savanna, and are harvested 180 to 270 days later. Care is needed during harvesting to minimize damage to tubers that lead to rot and a decrease in market value. Harvested tubers normally stay dormant (do not develop sprouts) for 30 to 120 days depending on environmental conditions, the date of harvest, and the species. This means that only one crop cycle is possible per year, possibly restricting supply.
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