Factors affecting diversity of Dioscorea species in Uganda

Abstract

The effects of drought, famine, distribution of land races, pests and diseases, deforestation, over-cultivation, introduction of new high yielding Dioscorea varieties, change in economic base, change in consumer preference, change in land use, status of transmission of indigenous knowledge and agricultural modernization on the diversity of Dioscorea were investigated in nine districts of Uganda. Three approaches were used: extensive eco-geographical survey, exploration and physical assessment. A structured questionnaire was used to capture information from the farming communities, government offices and local opinion leaders on the status of the yam in relation to farmlands, open countryside, protected areas and government departments in the nine target districts. Out of the 14 species recorded in Uganda the study showed that only seven species were available in the target areas. These included D. alata, D.dumetorum, D. odorotissima, D. bulbifera, D. rotundata, D. quartiniana, and D. schitnperianana. Reduction in the diversity of the yam was due mainly to serious genetic erosion at both inter- and intra-specific levels. Genetic erosion was mainly caused by lack of efficient propagation techniques, famine, pests, diseases, deforestation and lack of adequate promotion of the crop by the formal sector. The role played by the factors identified is discussed and recommendations for minimizing genetic erosion are given.