Identification of the endophytic bacterial isolates and their in vitro and in vivo antagonism against Ralstonia solanacearum

Seventy-three endophytic bacterial isolates obtained from the rootstocks of Solanum sp., widely distributed in Hanoi, Vietnam, were applied to Vitek32 system for their identification. Out of these, 29 isolates were tentatively identified as Chryseobacterium indologenes, Pseudomonas fluorescens, Chryseomonas luteola, Bacillus pumilis, B. megaterium, B. sphaericus, Sphingomonas paucimobilis, Enterobacter cloacae, Pantoea agglomerans, and Staphylococcus auricularis with the similarity ranging from 97 to 99% to the species covered in the system. Eight isolates with similarity less than 97% were also tentatively put into the relevant genus. However, the remaining 36 isolates could not be identified by this system. Thirty-seven identifiable isolates were evaluated for in vitro antagonism against Ralstonia solanacearum and disease suppression of bacterial wilt of tobacco. Thirteen isolates formed growth inhibition zones around their colonies placed on lawn of R. solanacearum as an indicator. The variation of anti-R. solanacearum activity spectrum within the endophytic bacterial species and isolates suggests that there could be different antibacterial substances participated in the antagonism. Most of the endophytic bacterial isolates have not significantly shown disease suppression. There was no significant correlation between antibiotic activity in vitro and disease suppression. For example, the tobacco plants treated with the isolate KuTox708, which was the least inhibitory to R. solanacearum in vitro, were significantly protected from bacterial wilt infection.