A potato wilt disease in South Africa caused by Erwinia carotovora subspecies carotovora and E. chrysanthemi

Abstract

In South Africa during the 1988 season, a wilt disease appeared in seed-potato crops. The disease was initially characterized by a one-sided wilt of the upper leaves, and in its advanced stage was indistinguishable from verticillium, fusarium and pseudomonas wilts. A basal stem rot was occasionally associated with wilted plants when wet, humid conditions prevailed. Erwinia carotovora ssp. carotovora and E. chrysanthemi were isolated from wilted plants, but E. carotovora ssp. carotovora was the predominant pathogen. Stem inoculations in the glasshouse showed that both pathogens were capable of causing wilt symptoms. An indication was found that E. chrysanthemi was more virulent at a higher temperature range (28-32°C) and E. carotovora ssp. carotovora at a lower temperature range (20-25°C). It was found that the potting compost, irrigation water and some parent tubers used for the propagation of plantlets at the Foundation Seed Scheme, Eastern Transvaal, were contaminated with E. carotovora ssp. carotovora.