Dioscorea spp.

Dioscorea is a genus with more than 600 species native to the Pacific Islands, Africa, Asia and America. Many Dioscorea species are cultivated and known as yams. Yams are an important source of carbohydrates, minerals, vitamins and dietary fiber for more than 100 million people in the humid and sub-humid tropics. Yams are also used to produce insecticides, to prepare poisons for hunting, and to produce birth control compounds and treatments for asthma and arthritis. Almost 90% of the global yam cultivated area and production is concentrated in Nigeria, Côte d’Ivoire, Ghana and Benin.

Three independent areas of domestications have been proposed, each of them bringing several Dioscorea species into cultivation: in Southeast Asia (D. alata, D. esculenta, D. bulbifera, D. hispida, D. pentaphylla, D. nummularia, D. opposita and D. japonica); in West Africa (D. rotundata, D. cayenensis, D. bulbifera, D. preussii, D. praehelensis, D. sansibarensis and D. dumetorum); and in pre-Columbian tropical America (D. trifida and D. convolvulacea). The earliest archeological remains of yams (D. hispida) date back to 20000 BP, and were found in Sarawak, Malaysia. Portuguese and Spanish navigators dispersed Asian yams to America. Today, yams of Asian origin (D. alata) are extensively grown in Africa and the Caribbean.

Farmers in mainland Africa and Madagascar continue to utilize wild yams, including by selecting plants from forests and bringing them into cultivation. These plants may be exposed to recurrent selection processes and hybridization with cultivated species.

Genesys displays information for almost 7,600 yam accessions, 92% of them traditional cultivars. Most of the accessions in Genesys are held at the genebank of the International Institute of Tropical Agriculture (IITA).

In 2010, a group of experts prepared the yam global conservation strategy. The strategy highlights the need to increase the representativeness of Dioscorea collections from the Americas and Asia and of minor cultivated species (other than D. alata and D. rotundata). The document also identifies yam ex situ collections that were not previously recorded, remarks on the urgency to improve in vitro and field conservation standards, and emphasizes the potential benefits of cryopreservation.

The yam global conservation strategy was revisited in 2021. The updated strategy proposed a network of ex situ collections dedicated to preserving maximum edible Dioscorea species diversity. The three main components of this strategy are: stratifying germplasm and detecting duplicates, creating elite subsets from 11 species, and broadening genetic diversity by preserving true seeds. The document also discusses challenges faced by curators and presents a project proposal with details on implementation, governance, and funding.

Given the importance of yams for food security and income generation in Africa, IITA and its partners are leading research efforts to improve two major cultivated yam species: white yam (D. rotundata) and water yam (D. alata). This initiative aims to produce high-yielding varieties of good quality and resistant to important diseases such as anthracnose and yam mosaic virus.