Abstract:

Field Agricultural and (NAARI) during the rains (LR), and at the 1995LR. systemic experiments were conducted at Namulonge Animal Production Research Institute short rains (SR) The studies and the 1995 long 1994 Kalengyere Research Station (KRS) during efficiency evaluated the insecticide infestation and (dimethoate) infection of in of preventing an aphid aphid-borne viruses in potato (Solanum tuberosum L.). conducted at NAARI in the house experiment was A screen 1995LR to establish the also, onset mature plant resistance to virus infection in potato in order application to critical of to limit insecticide spray periods of potato plants. The response of aphids to dimethoate spray treatment on growth seven Solanum potato varieties varied significantly between Kalengyere and Namulonge and, between aphid species infesting potato, particularly at Namulonge. This affected the ability of dimethoate to prevent aphid infestation and, consequently, the spread of aphid-borne viruses in potato. At Namulonge, dimethoate suppressed all potato infesting aphids except Myzus persicae (Sulz.). This led to heavy M. persicae infestation on sprayed than unsprayed potatoes. In contrast weekly dimethoate sprays effectively controlled aphid colonisation at sprayed potatoes. emergence. Kalengyere, and population Unsprayed potatoes at development Kalengyere in were heavily infested by aphids, with rapid aphid population growth occurring between the fifth and the sixth weeks after plant A comparison between Namulonge and Kalengyere showed that there was higher aphid pressure at Kalengyere than at Namulonge and, a higher aphid pressure at Namulonge during
the long rains than the short rains. The commonest potato aphid species caught in aphid traps we're not the most abundant aphid species from potato plants. In addition, correlations between total trap catches and aphid infestation indices from plants did not reveal significant and correlations consistent insecticide treatments. percentage trapped. of potato within However, plants seasons, locations and pooled data revealed that infested by aphid was significantly correlated with the total number of alate aphids Aphid collections from plants at Kalengyere showed that aptarae aphids adequately determined the proportion Namulonge and of a potato plant infested by aphids. At Kalengyere however, potato infestation by aphids was basically function of potatoes. alate aphids on Seed potato tuber indexing three aphid-borne potato both sprayed and unsprayed for viruses' latent infection with mechanically and one transmitted virus before planting indicated that Kalengyere Research Station has potential of providing seed potato free from aphid-borne viruses. However, seed from three of the seven varieties were infected with a mechanically transmitted virus. Attempt to prevent the spread of aphid-borne viruses in field grown potato using weekly spray of dimethoate spray at both NAARI and Kalengyere gave contrasting results. At NAARI, all the potato varieties used in the study were infected with potato leaf roll virus (PLRV) in the first season of introduction from Kalengyere to Namulonge, irrespective of them insecticide treatment. All the varieties were, however, free from potato virus Y (PVY) and potato virus S (PVS) infection. Kalengyere, the total effectiveness of dimethoate against all potato infesting aphid species and, the absence of aphid-borne viruses in field grown potatoes, probably indicate the ability of dimethoate to control aphids and aphid-borne viruses in Solanum potato at this site. It was also observed higher aphid pressure at Kalengyere there was then that whereas Namulonge there at was a Namulonge than at Kalengyere. greater virus pressure at Virus inoculation of screen house grown potato plants at ten-day intervals after plant emergence using potato leaf roll virus infected aphids showed that potato plants inoculated after flowering may produce seed tubers which are free from aphid-borne viruses. It was concluded from these studies that use aphicides in field grown potato, differences of various potato cultivars in susceptibility to both aphid and virus attack, and the on-set of mature plant resistance can reasonably reduce infection and spread of aphid-borne viruses in Solanum potato.