Biological control of potato bacterial wilt caused by Ralstonia solanacearum in Ethiopia: Determination of biovars of Ralstonia solanacearum

Ralstonia solanacearum is a very destructive pathogen that causes wilt in potato and many other solanacean crops in Ethiopia. In order to select effective antagonistic biocontrol agents for R. solanacearum strains, it is necessary to characterize the population of pathogenic strains. Therefore, 62 strains collected from wilted potato, tomato and pepper plants and potato tubers from the major potato producing regions of Ethiopia were characterized culturally and classified physiologically, based on their capacity to oxidize 3 disaccharides (lactose, maltose and cellobiose) and 3 hexose alcohols (mannitol, sorbitol and dulcitol). The results of this study indicated that all virulent strains from Ethiopia produce fluidal and irregular colonies with red centre and whitish periphery on triphenyl tetrazolium chloride (TZC) medium and irregular, fluidal, and creamy white colonies on casamino acids-pepton-glucose (CPG) medium. Physiologically, 19 strains were grouped to biovar I and 43 strains to biovar II. Previous studies from Ethiopia reported the availability of only biovar II of R. solanacearum. Thus for biovar I this is the first report concerning the Ethiopian R. solanacearum population.