Isolation and characterization of bacteria from different cacao progenies and their antagonistic activity against the black pod disease pathogen, Phytophthora palmivora

Abstract

The microbiota on cacao pod surfaces consists of an array of both pathogens and beneficial microorganisms. These beneficial microorganisms can easily be exploited for biological control of cacao pod pathogens as both have similar ecological niches. Bacteria population on pods of three cacao progenies, SCA 6, T85/799 and IFC 5, were determined using the plate count method on nutrient agar, Pseudomonas selective agar and tryptic soy agar. One hundred and six different isolates were obtained from the three cacao progenies. Out of this number, the antagonistic potential of 17 bacterial isolates against Phytophthora palmivora was investigated using agar plate and detached pod assays. The seventeen isolates were identified based on morphology, gram staining, biochemical tests compiled in API 20E plastic strips, biosurfactant production test and UV fluorescence assay. The 17 isolates could generally be classified into three genera: 15 were Pseudomonas, one Enterobacter sp. and another Neisseria sp. Thirteen out of the seventeen isolates significantly (p < 0.001) inhibited mycelia growth of P. palmivora on plates. Molecular analysis of sequences of two of the best-performing Pseudomonas isolates, coded 96 and 97, and grouped as fluorescent Pseudomonas spp. 1, revealed 100% similarity to Pseudomonas putida. The data support the hypothesis that these indigenous Pseudomonas putida isolates with GenBank access numbers KY508310 and KY5083110 produce antagonistic activity against P. palmivora and can be exploited either alone as biological control agents or incorporated in an integrated disease management for cacao black pod disease control.