Antibiotic and Antibacterial Activity of a Symbiotic Bacterium, Photorhabdus luminescens

Abstract

Antibiotic and antagonistic effects of primary and secondary forms of Photorhabdus luminescens, a symbiotic bacterium of an entomopathogenic nematode Heterorhabditis indica (RCR) were investigated in vitro against plant pathogens and beneficial microorganisms. An inhibition zone assay on potato dextrose agar (PDA) medium revealed that the primary form completely inhibited all plant pathogenic fungi, viz., Aspergillus flavus, Rhizoctonia solani and Fusarium solani and tested secondary form completely inhibited the growth of F. solani and partially inhibited A. flavus and failed to inhibit R. solani. However, dual culture assay on nutrient agar (NA) in both forms completely inhibited the growth of the bacterial pathogen, Xanthomonas punicae. The forms of P. luminescens did not inhibit the mycelial growth of entomopathogens viz., Metarhizium anisopliae, Verticillium lecanii and Nomuraea rileyi but inhibited the growth of bacterial bioagents Rhizobium sp. and Pseudomonas fluorescens. The present study indicates that P. luminescens can be effectively used in the management of these plant pathogens.