University of Reading, Reading, UK

Background and objectives
Yam production in West Africa, the Caribbean and the other yam-growing countries is constrained by several problems. One of the main production limitations is the scarcity of planting material caused by pest and disease attack [1]. In Ghana there is a paucity of information on the primary yam pathogens causing economic losses. The work presented here concerns the activities of a DFID-funded collaboration between UK and Ghanaian research institutes to investigate the nature and impact of yam diseases in Ghana. The research covers all the economically important yam pathogens, including fungi, nematodes and viruses. In particular, current work is investigating the relationship between the disease status of yam vines growing in the field and subsequent post-harvest diseases.

Results and conclusions
During a participatory rural appraisal, farmers identified anthracnose as the most important biotic constraint to yam production. The pathogen which causes yam anthracnose, Colletotrichum gloeosporioides, was found in over 95% of all yam foliage sampled in surveys throughout the yam-growing regions of Ghana. In around 10% of farms sampled, anthracnose levels on yam vines were sufficiently high to significantly reduce yield. In addition, viral diseases were present in over 90% of yams grown in the survey area. The three most common viruses identified during the survey were: yam mosaic potyvirus, yam potyvirus and Dioscorea alata badnavirus. Several parasitic nematodes on yam were also frequently associated with tuber tissue. The most commonly isolated nematode, Scutelonema bradys, was found in 59% of farms throughout Ghana.

1. Nwankiti AO, Arene OB, 1978. PANS 24, 486-494.