EVALUATION OF INSECTICIDAL PROPERTIES OF PROTEIN TOXINS OF THE SYMBIOTIC BACTERIUM Photorhabdus luminescens THOMAS AND POINAR AGAINST MAJOR SUCKING PESTS

Abstract

An investigation on efficacy of native isolates of Photorhabdus luminescens and their newlineformulations against major sucking pests Aphis gossypii (Glover), Phenacoccus solenopsis Tinsley newlineand Tetranychus macferlanei Baker and Pritchard was carried out at the Department of Agricultural newlineEntomology, College of Agriculture, Raichur, Karnataka, from 2021 2023. Total of three isolates of P. newlineluminescens were characterized and evaluated. The colony characters of all three isolates recorded newlinecircular to irregular, opaque to transparent with entire edge and raised in beginning and later which newlineremained undulated, sunken and flat. The colonies were brick/dark red at base with blue shades. All newlineisolates were gram negative, catalase positive, motile, bioluminescent. Further, P. luminescens isolates newlinewith 1500 bp length showed 16S rRNA gene sequence with 95-99 per cent similarity. All three newlineisolates were highly pathogenic to sucking pests resulting in cent per cent mortality within 48 hr. The newlinemedian lethal concentration of 2.02 × 102 newline, 2.35 × 107 newlineand 8.36 and#61620; 102 for cell-supernatant was recorded newlineagainst aphids, mealy bugs and mites, respectively at 48 h. Qualitative and quantitative enzyme assay newlinewere employed to quantify the extracellular enzymes and toxins of the bacterium through SDS-PAGE newlinegel electrophoresis. In all the isolates chitinase enzyme was produced in log phase (12-24 h), protease newlinein stationary phase (24-48 h) and lipase in late stationary phase (48-72 h). The protein bands obtained newlinebased on the molecular mass varied among the isolates with 66.4 kDa protein as common in most newlinevirulent isolates. Further, bio-assay of microencapsulated cell-supernatant formulation was carried out newlineto identify the optimum temperature and duration of storage. The microencapsulation of newline1x1010cells/mL of P. luminescens (UASR22PL1) cell supernatant and cells by emulsification method newlineyielded micron size (5.53 and 4.06 um, respectively). Among the three sucking pests, T. macferlanei newlinerecorded the lowest LC50 indicating higher susceptibility towards mi