Bacterial wilt caused by Ralstonia solanacearum has affected the potato industry in South Africa since 1914. Control of bacterial wilt is difficult and depends greatly on integrated management strategies. Little information is available on the longevity of R. solanacearum in soil under South African conditions and how it is influenced by cultural practices. Information regarding local weeds which can serve as alternative hosts is limited. Soil survival of R. solanacearum biovar 2 (race 3) was investigated in an artificially infested field managed by either one of four cultural practices, namely maize and potato monoculture, bare and weed-fallow. After a five-year period wilting of indicator plants was observed in all treatments with potato the highest, followed by bare-fallow, maize monoculture and lastly weed-fallow. Results demonstrated a greater ability of biovar 2 to survive in soil than generally accepted. Subsequently, the susceptibility of 22 weed and three grass species was investigated in the greenhouse. Five species were susceptible to biovar 2 and 13 to biovar 3. Preliminary in vitro studies conducted to determine suppressiveness of some weeds/grasses, indicate that microbial activity associated with some weeds could be involved in suppression of the wilt organism. Further studies are however required. The effect of maize on Ralstonia solanacearum populations was evaluated in a pot trial as well as in hydroponic culture. Results indicated that microbial populations present in the maize plant, could play a role in the susceptibility of maize to bacterial wilt infection. Antagonistic bacteria associated with some maize plants or with the maize rhizosphere could be partly responsible for suppression of wilt.
Dissertation (MSc Agric (Agronomy))--University of Pretoria, 2006.