Pseudomonads: major antagonistic endophytic bacteria to suppress bacterial wilt pathogen, Ralstonia solanacearum in the eggplant (Solanum melongena L.)

Endophytic bacteria of eggplant, cucumber and groundnut were isolated from different locations of Goa, India. Based on in vitro screening, 28 bacterial isolates which effectively inhibited Ralstonia solanacearum, a bacterial wilt pathogen of the eggplant were characterized and identified. More than 50% of these isolates were Pseudomonas fluorescens in which a vast degree of variability was found to exist when biochemical characteristics were compared. In greenhouse experiments, the plants treated with Pseudomonas isolates (EB9, EB67), Enterobacter isolates (EB44, EB89) and Bacillus isolates (EC4, EC13) reduced the wilt incidence by more than 70%. All the selected isolates reduced damping off by more than 50% and improved the growth of seedlings in the nursery stage. Most of the selected antagonists produced an antibiotic, DAPG, which inhibited R. solanacearum under in vitro conditions and might have been responsible for reduced wilt incidence under in vivo conditions. Also production of siderophores and IAA in the culture medium by the antagonists was recorded, which could be involved in biocontrol and growth promotion in crop plants. From our study we conclude that Pseudomonas is the major antagonistic endophytic bacteria from eggplants which have the potential to be used as a biocontrol agent as well as plant growth-promoting rhizobacteria. Large scale field evaluation and detailed knowledge on antagonistic mechanism could provide an effective biocontrol solution for bacterial wilt of solanaceous crops.