Impact of yam mosaic virus (YMV) on tuber yield of white yam ( Dioscera rotundata Poir ) in Ghana

The impact of Yam mosaic virus (YMV) on tuber yield of white yam (Dioscorea rotundata Poir) in the forest zone of Ghana was assessed under controlled environment and in the field at Kumasi, Ghana. Two field trials were carried out in 2001 and 2002. The experiment under controlled environment was conducted in 2003. In the controlled environment, white yam developed from tissue culture were mechanically inoculated with sap extracts of YMV infected leaves. The inoculated plants were grown alongside known YMV infected white yams not cleaned with tissue culture as well as non inoculated healthy controls cleaned with tissue culture and virus indexed. In the field trial, data taken were disease severity and yield per plant after harvest. Plants raised from non tissue culture cleaned seed yam showed severe symptoms of YMV with a yield loss of 53% as against 28% for the inoculated plants. In the two field trials in 2001 and 2002, mean yield losses of between 26.0% and 89% were recorded depending on disease severity. This implies YMV on white yam is economically important. This study is the first of such in Ghana. Efforts to control yam mosaic virus disease through the application of biotechnology to produce virus-free planting materials as well as the use of resistant varieties should be intensified to improve yield, thereby increase income of resource-limited yam farmers. Key words: Dioscorea rotundata, Yam mosaic virus, disease severity, tissue culture, yield