Colonization of eggplant by endophytic bacteria antagonistic to Ralstonia solanacearum, the bacterial wilt pathogen.

Abstract

Bacterial wilt caused by the vascular pathogen Ralstonia solanacearum is a major constraint for cultivation of eggplant (Solanum melongena L.) in the state of Goa, India. Three strains of endophytic bacteria isolated from xylem sap of eggplant and antagonistic to R. solanacearum were evaluated for colonization of eggplant cv. Agassaim under greenhouse conditions. Results suggest that rifampicin resistant mutants XB1R (Agrobacterium tumefaciens), XB99R (Enterobacter sp.) and XB177R (Bacillus cereus) exhibit varying degree of colonization of endophytic tissues and rhizosphere soil of eggplant. XB177R colonized eggplant most efficiently and systemically from rhizosphere (6.5 Log cfu g-1) to leaves (4.34 Log cfu g-1) until 30 days after inoculation. Green Fluorescent Protein tagged XB177 colonized rhizoplane, cortex and xylem vessels of eggplant grown under greenhouse conditions. Studies on changes in the population of XB177R during bacterial wilt infection suggested that its endophytic population of 5.48 log cfu g-1 fresh weight and rhizosphere population of 6.18 log cfu g-1 of rhizosphere soil was necessary to control bacterial wilt in eggplant. Further, it is reported that pre-treatment of eggplant is an important pre-requisite for effective wilt prevention by the antagonistic bacteria. The present study demonstrates the importance of plant colonization ability of antagonistic bacteria for bacterial wilt control.