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Colonization of Eggplant by Endophytic Bacteria Antagonistic to Ralstonia solanacearum, the Bacterial Wilt Pathogen

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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.

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Financial support from Indian Council of Agricultural Research (ICAR), New Delhi, through “Outreach project on Phytophthora, Fusarium and Ralstonia diseases of horticultural and field crops”-(PhytoFuRa) and the facilities provided by the Director, ICAR-Central Coastal Agricultural Research Institute (formerly known as ICAR Research Complex for Goa), Goa, India, are greatly acknowledged. The authors are thankful to Dr. Daniel Zeigler, Bacillus Genetic Stock Centre, Ohio State University, Columbus, USA for providing the GFP vector pAD43-25, Prof. Jo Handelsman, Yale University, Connecticut, USA for E. coli strain GM2929 and Prof. S. K. Dubey, Department of Microbiology, Goa University for the E-porator facility.

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Correspondence to Gauri A. Achari or R. Ramesh.

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Significance statement Bacterial wilt caused by Ralstonia solanacearum is a major constraint for cultivation of eggplant in India. Study on colonization of eggplant by antagonistic endophytic bacteria reveals successful colonization of bacteria in eggplant and pre-treatment of eggplant with antagonistic bacteria is an important pre-requisite for effective suppression of bacterial wilt.

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Achari, G.A., Ramesh, R. Colonization of Eggplant by Endophytic Bacteria Antagonistic to Ralstonia solanacearum, the Bacterial Wilt Pathogen. Proc. Natl. Acad. Sci., India, Sect. B Biol. Sci. 89, 585–593 (2019).

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  • Antagonistic bacteria
  • Bacterial wilt
  • Endophytic bacteria
  • Plant colonization
  • Ralstonia solanacearum