Evaluation of Pseudomonas fluorescens Isolates as Biocontrol Agents Against Bacterial Wilt Caused by Ralstonia (Pseudomonas) solanacearum

Abstract

A total of 50 fluorescent pseudomonas isolates collected from different potato growing areas in Ethiopia were evaluated on King’s B medium for antibiosis towards Ralstonia solanacearum, the pathogen of bacterial wilt of potato. Only three isolates, Pf S2, Pf Wt3 and PfW1, showed inhibitory effect on the growth of the pathogen. The three isolates were evaluated for their antagonistic effect in a greenhouse experiment. Tubers of potato clone CIP 383031.15 that was susceptible to bacterial wilt were bacteriazed in a 48 hour old culture suspension of the three isolates and Pfri, a reference strain from India, for 2 hr and planted in pots containing sterilized
soil. Plants that were 2 -3 leaves old were inoculated with the pathogen with a concentration of 106 cfu/ml. Non-dipped tubers but inoculated with the pathogen and bacteriazed and inoculated plants were used as controls. Bacteriazation of tubers with Pf S2, Pf Wt3, and PfW1 significantly reduced disease incidence compared to the pathogen-inoculated control and increased plant growth, i.e., plant height and dry weight. There was higher plant growth due to bacteriazation of tubers with PtWt3 (76.9%) followed by PtS2 (59.8%). The study findings indicated the importance of the antagonistic isolates as biological control agents and plant
growth-promoting rhizobacteria.