Identification of the Endophytic Bacterial Isolates and their in vitro and in vivo Antagonism against Ralstonia solanacearum

Abstract

Seventy-three endophyiic bacterial isolates obtained from the rootstocks of Solawam 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 sirnilarity ranging from 97 to 990/0 to the species covered in the system. Eight isolates with sirnilarity less than 970/0 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 i7~ vitro antagonism against Ralstonia solanacearum and disease suppression of bacterial wllt of tobacco. Thirteen isolates formed growih inhibition zones around their colonies placed on lawn of R. sola7~acearum as an indicator. The variation of anti-R. solauacearum activity spectrum within the endophytic bacterial species and isolates suggests that there could be different antibacterial substances participated in the antagonism. Most of the endophyiic bacterial isolates have not significantly shown disease suppression. There was no significant correlation between antibiotic activity i?e vitro and disease suppression. For example, the tobacco plants treated with the isolate KuTox708, which was the least inhibitory to R. solavtacearum i7h vitro, were significantly protected from bacterial wilt infection.