Glossary of Yam Terms #

This glossary defines key terms used throughout the YamBook. Understanding these terms builds the vocabulary needed to read, study, and communicate about yams with precision.

C #

Curing #

The post-harvest process of holding harvested yams at warm temperature (25–30°C) and high relative humidity (85–95%) for 4–7 days to allow wound healing and skin hardening before long-term storage. Skipping curing dramatically reduces storage life. Also called hardening in some regions.

Cyanogenic Glycosides #

Natural plant compounds that release hydrogen cyanide when damaged or consumed. Found in some yam species (especially Dioscorea dumetorum). Proper preparation (soaking, boiling, fermentation) is required to render these safe.

D #

Dioscorea #

The genus that contains all true yams. Named after the ancient Greek physician Dioscorides. Includes over 600 species, of which approximately 10 are widely cultivated for food. Dioscorea alata (white yam) and D. rotundata (Guinea yam) are the most important food species.

Dormancy #

The period after harvest during which a yam tuber will not sprout even under favorable conditions. Dormancy breaks naturally over time and is influenced by species, storage conditions, and whether the tuber was cured. Breaking dormancy prematurely (such as by cutting) results in rapid sprouting and weight loss.

Dry Matter Content #

The proportion of a yam tuber that is solid material (mostly starch) rather than water. Higher dry matter means a denser, heavier tuber that is better for certain preparations (frying, pounding) but may cook differently than lower dry matter varieties. Typically 20–35% in food yams.

F #

Fufu #

A West African staple food made by pounding cooked yam (or cassava) with a mortar and pestle until a smooth, elastic dough is formed. The word refers to the process as much as the product. Fermented fufu has a sour tang from natural lactic acid fermentation.

Fusarium #

A genus of fungi that causes storage rot in yams. Fusarium species enter through wounds and bruises sustained during harvest and can spread through a storage pile rapidly in warm, humid conditions.

G #

Garri #

A granulated fermented cassava product (not yam, but similar processing applies). The name is sometimes applied loosely to processed yam products in West African markets. Represents the broader category of value-added root and tuber products in the region.

Germplasm #

The genetic material—seeds, tubers, plant tissue—held in conservation collections. Yam germplasm banks (such as those at IITA in Nigeria) preserve the genetic diversity of cultivated and wild yam species against disease, climate change, and the loss of traditional varieties.

Guinea Yam #

Common name for Dioscorea rotundata, the most important food yam in West Africa. Called “Guinea” for the Guinea Coast region. Distinguished by its round to cylindrical tubers with white to cream flesh. The primary yam of Nigerian and Ghanaian cuisine.

M #

Mounding / Ridge #

The agricultural practice of piling soil into mounds or ridges before planting yams. Mounds improve drainage, make harvesting easier, reduce soil compaction around developing tubers, and allow the farmer to monitor tuber development. Spacing and mound size are determined by species expected tuber size.

Mucilage #

A sticky, slimy substance produced by some yam species when cut or cooked. Contains complex polysaccharides. More pronounced in some species (D. bulbifera) than others. Can be reduced by proper preparation methods.

P #

Polyploidy #

The condition of having more than two complete sets of chromosomes. Many yam species are polyploid (triploid, tetraploid, hexaploid), which complicates breeding because trait inheritance becomes unpredictable and generation cycles lengthen.

Propagation (Vegetative) #

Reproduction of yam plants from tuber pieces (setts) rather than seeds. Setts are cut from a mature tuber and planted; each sett produces a genetically identical plant. This is the dominant method of yam cultivation because it preserves desirable traits and produces uniform crops, but it also propagates diseases and limits genetic diversity.

S #

Senescence #

The natural aging process of the yam vine, signaled by yellowing and death of the above-ground foliage. Senescence marks the end of the growing season and the point at which tubers reach maximum size. Delayed harvest after senescence increases fiber development and rot risk.

Sett #

A cut piece of yam tuber used as planting material. A sett typically weighs 200–500g and is cut from the head (crown) portion of the tuber, which has more eyes/sprout buds. The practice of using setts is the foundation of yam vegetative propagation.

Staking / Trellising #

The practice of providing support (stakes, poles, strings, trellises) for yam vines to climb. Staking improves air circulation (reducing disease), makes harvesting easier, can increase tuber size, and facilitates farm operations. In some systems, yams are left to trail on the ground.

Starch Granules #

The microscopic crystalline structures inside yam cells where starch is stored. Granule size, shape, and composition affect how the yam behaves during cooking—gelatinization temperature, thickening power, and texture all derive from granule properties.

V #

Vine Senescence #

The death and drying of the yam’s above-ground vine at the end of the growing season. The most reliable field indicator that tubers have reached physiological maturity and are ready for harvest. The vine drying out is not the same as the vine dying back—it must dry completely.

Virus (Yam Mosaic Virus, Yam Mild Spotted Virus) #

A range of viruses infect yams, causing mosaic patterns on leaves, stunting, and reduced tuber quality. Viruses are transmitted through vegetative propagation (setts carry them from generation to generation) and by insect vectors. Virus elimination through tissue culture is an important breeding tool.