Occurrances and distribution of some tobacco viruses in Southern,Central and Lusaka provinces in Zambia

Abstract

Nine tobacco fields of small and large scale farmers in Southern,Central and Lusaka provinces of Zambia were surveyed for the occurrence and distribution of virus diseases during tobacco growing season in 1997.Three tobacco fields in each province were selected for virus detection and sample collection.During this survey,infected tobacco plants were examined and disease symptoms recorded.Virus infected weed occurring in or near the tobacco crop were included to determine if they served as virus reservoir along with potential insect vectors.Virus infected tobacco leaf samples were inoculated on a panel of differential hosts to identify the commonly occurring viruses on tobacco in Zambia.Sap from field infected and symptomatic greenhouse plants were tested serologically using DAS-ELISA.Viruses were identified if they gave positive reaction against antisera from Agdia Inc.,USA.Virus particle morphology was also studied in some cases by electron microscopy. The results indicated that at least four viruses-tobacco mosaic(TMV),potato virus Y(PVY),alfalfa mosaic(AMV) and tobacco ringspot(TRSV)occur in tobacco in Zambia. Tobacco mosaic virus(TMV) was recovered in 77% of diseased samples while PVY was recovered in 66.6% and TRSV in 22%. Obviously TMV and PVY are the more common occurrence.The prevalence of TMV and PVY in all the three provinces indicate that these viruses could be responsible in limiting tobacco production in Zambia. It is therefore important that the scope of the virus disease occurring in Zambia should be broadened to identify all the viruses and their impact on tobacco if satisfactory management strategies are to be worked out.