Incidence of potato (solanum tuberosum l.) viruses and effect of maize border crop placement on aphids and virus II diseases
A survey was carried out using structured questionnaire in six districts and twelve markets to establish seed potato production practices and incidence of potato viruses in farmers' produced seeds. Samples of potato tubers were also collected for serological analysis of viruses using Double Antibody Sandwich Enzyme-Linked Immunosorbent Assay method. A field experiment was also conducted at National Potato Research Centre, Tigoni over two seasons to determine the effect of maize border crop placement on aphids and aphid-transmitted viruses in Irish potatoes. The maize border was placed at 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 metres. Data collected from the field experiment was on population of aphids, virus disease incidences, virus titre, plant height and tuber yield. Data obtained was analyzed using Statistical Package for Social Science and GenSat software. The survey revealed that all the farmers interviewed had used their own seed potato and only 1.6% of the farmers sourced seed from research stations. Tigoni was the most preferred variety by most farmers (25.8%), while Nyayo was the most preferred variety by the traders. Farmers considered high yields in the choice of a new variety and chemical control was the most preferred method for the control of pests and diseases. Fifty percent and 49.2% of the farmers had seen virus disease symptoms and aphids in potatoes respectively. Majority of the farmers (46.7%) obtained less than 2 tons/acre. The incidence of virus and virus titres in tubers differed among districts and retail markets and the viruses detected were potato leaf roll virus, potato virus A, potato virus M, potato virus S, potato virus X and potato virus Y. Potato virus S was the most prevalent viruses in the farmers' produced seed potato. There were significant differences among the districts in the incidence of all the viruses, except potato virus A and potato virus S. There were significant differences among the districts in the titre of all the viruses except Potato leaf roll virus and Potato virus Y. From the field experiment the aphid species identified were, Myzus persicae, Macrosiphum euphorbiae, Aphis gossypii, Aphis fabae and Rophalosiphum maidis. The most abundant aphid species on the leaves during long rain season was M euphorbiae while, A. gossypii was the most abundant in short rain season. R. maidis was the most abundant species in yellow waterpan traps during both seasons. Placement of maize border up to 1.5m and 1.0m had a significant reduction in virus disease incidences by upto 50% and 60% during short rain and long rain seasons respectively. Lowest virus titre was recorded in tubers from plots with maize border placed at 0.5 m and 1.0 m from potato while the lowest tuber yield was recorded in potato plots with maize border placed at 0.5 m. Maize border crop can be used by farmers to reduce transmission of aphids and aphidtransmitted viruses in Irish potatoes. The effective distance for the placement of maize border is 1.0 m. However, there is need to carry out research to determine the number of seasons a farmer can plant seed potato harvested from plots with maize border crops before yields are reduced to uneconomical level.