The Effect of Temperature, Storage Period and Inoculum Concentration on Symptom Development and Survival of Ralstonia solanacearum in Inoculated Tubers

Abstract

Bacterial wilt is a devastating disease in South Africa and causes financial losses for producers of a number of crops like potato, tomato, pepper, and tobacco (Swanepoel, 1988). Every year valuable farmland is withdrawn from potato production as a result of new infections, probably arising from latently infected potato tubers. It is commonly believed that cold storage of tubers infected with Ralstonia solanacearum, renders the organism non-viable. However, Nielsen (1963), found that the pathogen survives in potato tubers and in culture at low temperature. Ciampi et al., (1980) and Ciampi-Panno et al., (1981) reported that storage at 4 °C did not eliminate the pathogen from inoculated tubers even after 40 days. Ciampi et al., (1980) found that the bacterial population declined drastically after one day in tubers stored at 4 °C, (compared to those stored at higher temperatures) and reached a level of only a few or no viable cells after three weeks. The movement of R. solanacearum has been monitored in resistant potato plants, but not in potato tubers (Ciampi-Panno et al., 1981). Skoglund et al. (1993) after personal communication with El-Nashaar, reported that the location of the bacteria inside the tuber changes during storage. No literature describes disease development inside tubers at different temperatures, or how different inoculum concentrations affect symptom development over time. The aim of this study was to investigate the concept of cold storage as a possible method of eliminating latent infections.