An improved method for selection of antagonistic bacteria against Phytophthora capsici Leonian infections in black pepper (Piper nigrum L.)

Abstract

An improved and rapid method for selection of bacteria primarily based on its inhibitory effect on pathogenesis of Phytophthora capsici on black pepper (Piper nigrum) was developed. Reductions in mycelial growth of P. capsici in dual plating assay and inhibition of lesion on excised black pepper shoots in planta assay were calculated. The inhibition ranged from 0.0% to 92.8% among the 19 bacterial isolates tested against P. capsici in the in planta assay III where the bacterized shoots were challenge inoculated with P. capsici. The in planta assay III could select only two bacterial strains among the 19 isolates as effective against P. capsici whereas, four and six bacterial strains in the in planta assays I and II, respectively. The dual plate method, where only two-way interaction between the pathogen and antagonist was studied, could select four bacterial strains as effective ones. The in planta selected bacterial strains could protect the black pepper plants from foot rot infection when tested in the nursery. The in planta assay based on this three-way interaction among black pepper (host)- P. capsici (pathogen)-candidate bacterial strains (antagonist) was found to be an effective method to select antagonistic bacteria against the foot rot pathogen.