Abstract:

Seven potato (Solanum tuberosum Lin.) varieties previously indexed against potato leaf roll virus (PLRV), potato virus Y
(PVY), potato virus S (PVS) and potato virus X (PVX) were grown in the field for two seasons at Namulonge representing
warm, mid-altitude tropics and, for one season at Kalengyere representing cool highland areas. One set of the seven potato
varieties was sprayed with dimethoate at a rate of 1.19 kg a.i. ha'1 at weekly intervals to prevent aphid infestation and
spread of aphid transmitted viruses. The second set was not treated. Seed tuber indexing before planting showed the
absence of aphid transmitted viruses (PLRV, PVY and PVS) in seed potato obtained from Kalengyere during both seasons.
Weekly collection of aphids at both sites showed a predominance of Myzus persicae (SuL), the principle vector of most
potato viruses. Dimethoate controlled aphids at Kalengyere but not at Namulonge. As a result, seed potatoes obtained
from Kalengyere and grown at Namulonge acquired the aphid-transmitted PLRV in the first season of growth whether
they were treated with the insecticide or not. However, all the varieties were free from PVY and PVS. At Kalengyere, all the
varieties grown in the field were free from aphid-borne viruses irrespective of the insecticide treatment. These results
indicate that there'is probably M. persicae resistance to dimethoate at Namulonge.