Abstract

Plant growth-promoting rhizobacterial (PGPR) strains were tested for their efficacy against the Coleus root rot pathogen Macrophomina phaseolina under in vitro, glasshouse and field conditions. Among the thirty isolates ofP. fluorescens screened under in vitro condition, six isolates viz., Pf1, FP 7, COTP-20, COGP-30, TDK-1 and AH-1 were effective in reducing mycelial growth of the pathogen. The isolate Pf1 showed maximum percent inhibition over control which contributes 58.52% reduction over control, followed by FP 7. Mode of action of effective PGPR isolates was studied by testing the production of indole acetic acid (IAA), siderophore, lytic enzymes, hydrocyanic acid (HCN), volatile metabolites, fluorescein and pycovyanin. Among these six isolates, Pf 1 and FP 7 found to produce all these compounds in higher quantity in comparison with other isolates. Plants treated with talc based formulation of Pf1 (stem cuttings dip + soil application) significantly increased the activity of defence related enzymes viz., peroxidase and poly phenol oxidase in coleus plants followed by FP 7 (Stem cuttings dip + soil application) when compared to untreated control. The plants treated with pre mixture fungicide (Carbendazim + Mancozeb) (stem cuttings dip + soil application) at 0.1% effectively reduced root rot incidence over control followed by Pf1 (stem cuttings dip + soil application) at 0.2% under both pot and field conditions. Plants treated with Pf1 (Stem cuttings dip + Soil application) showed best performance of both growth and yield parameters followed by FP 7 (stem cuttings dip + soil application) under both glass house and field conditions.

Key words: Biocontrol, Pseudomonas fluorescens, root rot, Macrophomina phaseolina, induced systemic resistance, defence enzymes.