Plant growth promotion and suppression of bacterial wilt incidence in tomato by rhizobacteria, bacterial endophytes and the root endophytic fungus Piriformospora indica

Abstract

Four strains each of rhizobacteria and endophytic bacteria, and the root colonizing beneficial fungus Piriformospora indica were assessed for their biological control potential against tomato bacterial wilt disease caused by Ralstonia solanacearum. Two endophytic bacterial isolates, Bacillus velezensis PCSE10 and Streptomyces leeuwenhoekii KBT004 and one rhizobacterium Bacillus amyloliquefaciens VLY24 showed direct in vitro antagonism against the pathogen. Culture filtrate of B. velezensis PCSE10, B. amyloliquefaciens VLY24 and P. indica inhibited the growth of the pathogen. Among the eight bacterial strains, only Rhizobium radiobacter PCRE10 and S. leeuwenhoekii KBT004 were found to be compatible with P. indica in dual culture plate assay. Two varieties of tomato, Naveen (highly wilt susceptible hybrid) and Vellayani Vijay (moderately wilt tolerant selection) were used to evaluate the biocontrol efficacy of the bacterial bioagents and the fungal endophyte, both individually and in combinations. Disease incidence in Naveen after 21 days of pathogen inoculation was the minimum (15%) when seeds were treated with R. radiobacter PCRE10. In Vellayani Vijay, seed treatment with S. leeuwenhoekii KBT004 was the best individual treatment with a disease incidence of 30%. Treatment with P. indica showed similar results in both the varieties with 40% disease suppression. This is the first report of involvement of P. indica in suppression of a bacterial plant pathogen. Combined inoculation of P. indica with selected compatible bacterial agents did not show any promising results. However, in the nursery, seed treatment with all the bioagents showed improved seedling growth when compared with untreated control.