Antagonistic effects of metabolites of Pseudomonas fluorescens strains on the different growth phases of Phytophthora capsici, foot rot pathogen of black pepper (Piper nigrum L.)

Abstract

Foot rot of black pepper caused by Phytophthora capsici causes heavy crop losses. Ecofriendly biological control was given high priority in the Integrated Disease Management programs (IDM). Strains of P. fluorescens which were antagonistic to P. capsici, the foot rot pathogen in black pepper produced inhibitory metabolites. Up to 72% inhibition of mycelial growth of P. capsici was observed in dual culture experiments. The metabolites of P. fluorescens strain, IISR-6 completely inhibited the sporangial production the most explosive phase in P. capsici. The indirect germination of sporangia (release of zoospores) also was inhibited considerably. The percent inhibition varied from 89 – 98%. The germination of zoospores of P. capsici was negatively influenced by the metabolites of P. fluorescens. Up to 90% inhibition of germination was noticed. Partial characterization of the metabolites let to the detection of two antibiotics – Pyoluteorin and pyrrolnitrin. The volatile metabolites of P. fluorescens also inhibited the different phases in life cycle of P. capsici, particularly mycelial growth and production of sporangia. HCN was detected in the volatile metabolites of the bacterial strains in varying quantities. The results are discussed in relation to the mechanism of disease suppression.