On-farm successes and challenges of producing bacterial wilt-free tubers in seed plots in Kenya

Shortage, unavailability and high cost of disease-free seed potato and Ralstonia solanacearum-infested soils have remained key limitations in the management of potato bacterial wilt in Kenya. Attempts to reduce yield losses caused by the disease have been made through on-farm development and promotion of a seed-plot technique which enhances availability of disease-free seed tubers and acts as a window for the introduction of other bacterial wilt management practices to small-holder farmers. Two major potato-producing regions in Kenya, South Kinangop and Meru, which have differences in farmer preferences to potato varieties, disease constraint levels, land use, weather and cropping patterns, were used for evaluation of the seed-plot technique. Certified potato tubers were planted at a spacing of 20 cm by 20 cm in seed plots and at 75 cm by 30 cm in ware plots, the latter simulating farmers' management practices. Data collected included tuber yields and disease incidences. High density planting in seed plots significantly increased land productivity for total tubers per unit area in comparison with low planting density in both experimental regions. In South Kinangop, varieties Tigoni and Roslin Tana produced 2.54 and 2.36 times more tubers per unit area, respectively, in seed plots than in ware plots; in Meru, land productivity was increased 2.08 and 6.75 times for varieties Asante and Kerr's Pink, respectively, planted at seed-plot density. Increases in land productivity were a function of both the planting density and disease pressure. Within five consecutive plantings, bacterial wilt in South Kinangop declined to insignificant levels on farmers' fields. However, seed plots and ware plots alike were infested with the disease in Meru within the first season after planting certified, disease-free seed tubers; in some cases, the disease was introduced by farmers through contaminated feet/shoes as evidenced by occurrence of diseased plants at the seed plot edges. Key Words: Bacterial wilt control, disease-free tubers, multiplication, seed availability, small-holder farms (African Crop Science Journal 2001 9(1): 279-286