| dc.description.abstract | 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.
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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. | en |
