Aggressiveness of Ralstonia solanacearum Strains and Evaluation of Tomato Genotypes for Resistance

Abstract

Twenty-nine Ralstonia solanacearum strains collected from tomato, potato and pepper in Ethiopia were evaluated for their aggressiveness on four tomato cultivars differing in level of bacterial wilt resistance. The strains evaluated were categorized into three aggressiveness groups namely Aggl, Agg2 and Agg3 with proportion of 7, 41 and 52 % of tested strains respectively in an increasing virulence pattern. The most aggressive strain group (Aggl) consists of biovar 1 and racel strains and the other groupings did not show correlations to biovar, host or geographical origin. Sources of resistance against the highly aggressive strain, TomNa3 (biovar 1/race 1) was evaluated in growth chambers in comparison to Toudk2 (race 1 biovar 3) originated from Thailand. Wilt incidence, percent severity index and corresponding areas under disease progress curves were used to evaluate level of resistance. Among thirty-three tomato genotypes, six genotypes were identified as resistant and eleven as moderately resistant to the Ethiopia highly aggressive strain (TomNa3). Differential reactions were observed with some genotypes based on the strain of R. solanacearum used. All tomato cultivars commonly grown in Ethiopia were found either susceptible or highly susceptible to the most aggressive strain of R. solanacearum of Ethiopia and Thailand. The study recommends a breeding program incorporating resistant sources into existing tomato cultivars or evaluating the identified resistant sources for desirable agronomic traits.