Effect of cultivar and thermotherapy combined with meristem-tip culture on eliminating prevalent viruses infecting potato in Uganda
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Potato (Solanum tuberosum) is an important crop in eastern and south-western highlands agro-ecological zone of Uganda where it is suitable for bridging periods of food shortage. However, production is constrained by viruses which reduce yield through accelerating tuber degeneration. Current management practices include serological indexing of mother plants to identify virus free plants for initiating in tissue culture. Healthy tissue culture plantlets are subsequently used to produce clean mini-tubers which are bulked in open fields to obtain sizeable amounts of pre-basic and basic seed. This process is characterized by low multiplication rates, requiring several generations of field multiplications to produce sizable amounts of seed. Repeated multiplications result in progressive virus infections leading to seed degeneration and subsequently dropping high yielding cultivars from the seed system. This process can be reversed by efficient virus elimination methods whose success depends on type of virus, plant species and cultivar type. Therefore this study generally aimed at evaluating and determining appropriate procedures for virus elimination from selected potato cultivars in Uganda. Specific objectives of the study were: (i) to establish the incidence and distribution of major potato viruses in key potato producing districts of Uganda and then (ii) establish the optimum temperature exposure period for maximum virus elimination from selected virus-infected potato cultivars. Leaf Samples were collected from farmers’ fields and assayed for viruses using double antibody sandwich-enzyme linked immunosorbent assay (DAS-ELISA) aided by a plate reader at 405 nm wavelength. Prevalent viruses were eventually subjected to thermotherapy for 0, 2, 3 or 4 weeks at 37-400C; 16 hours of light and 30-340C; and 8 hours of darkness. The study identified four of the six most important viruses; Potato virus X (PVX), Potato virus S (PVS), Potato virus M (PVM) and Potato leafroll virus (PLRV) at 64.9, 78.9, 3.1 and 21.2 % incidencies respectively across districts. Results indicated that virus elimination efficiency significantly (P≤0.05) varied between the four virus elimination treatments, cultivars and viruses.