Effect of aphids and aphid transmitted viruses in seed potato (solanum tuberosum l.) production by small scale farmers in Kenya
Small scale fanners contribute 99% of the seed potato produced and used in Kenya. Virus diseases cause degeneration of seed potatoes leading to low yields and low incomes to farmers. The study was carried out to determine the levels of aphids and viruses in fannerproduced seed potato system and to evaluate the associated yield losses. A survey was carried out to determine the seed potato practices among small scale fanners and the incidence of aphid transmitted potato aphid viruses in the fanner produced seed potato. Samples of potato tubers were collected from each fanner and analyzed for presence of viruses using DASELISA test. On farm monitoring studies were carried out among fanner-based seed potato producers in Njabini and Limuru where 120 seed potato fanners from four seed potato producer groups were trained on identification and management of aphids and virus diseases in seed potato production. Results of the study showed that 70% of fanners obtain seed potato from local markets and seed potato producing fanner groups. The main potato varieties grown in order of decreasing frequency in Njabini were Tigoni, Changi, Kimande and Mwezi Moja while in Limuru, Tigoni, Nyayo, Asante and Mwezi moja. Majority of the farm sizes are 1-5 acres and the area under potato was less than an acre per fanner. Most fanners applied fungicides for control of late blight but none had any knowledge 6f virus diseases and very few applied pesticides to manage insect pests. Only 22% of fanners in Njabini knew about existence of aphids in potato and none in Limuru. Most of the potato tuber samples were infected with potato leaf roll virus (PLRV) and potato virus S (PVS). Other potato viruses detected were potato virus M (PVM), potato virus X (PVX), potato virus Y (PVY) and potato virus A (PVA). Aphid species identified were Myzus persicae, Macrosiphum euphorbiae, Aphis gossypii, Aphis fabae and Rhopalosiphum maidis. The most prevalent was A. gossypii and M euphorbiae. Higher aphid population was detected using water traps. (xiii) Virus disease incidence was higher in Limuru than Njabini and the most prevalent virus was PVS followed by PLRV and PVM while the least prevalent was PVY. Healthy looking plants had a latent virus infection rate of 57.2% compared to 76.6% for plants showing virus symptoms. Healthy-looking plants yielded more and heavier tubers and virus infection reduced the number of tubers by between 10.0 to 35.5% while tuber weight was reduced by up to 63.0%. Training improved farmers' knowledge in management of aphids and potato Viruses. The results indicated that most farmers use virus-contaminated seed potato and that knowledge on potato aphids and virus diseases was non-existent. The results indicated high virus disease prevalence levels in the farmers' fields.,Given that most farm holdings are less than 5 acres and that aphid management is not practiced, the spread of virus diseases among different farms could be very high. There is need to train farmers and agricultural extension staff in management of aphids and aphid transmitted viruses for increased potato yields. In addition, more studies on the rate of seed potato degeneration would be needed to determine the number of seasons a clean stock can be re-used for seed production without significant yield reduction.