Induction of defence responses in cacao against Phytophthora palmivora by Pseudomonas chlororaphis CP07

The objective of this study was to evaluate the effect of Pseudomonas chlororaphis CP07, isolated from the rhizosphere of cacao, on the induction of defence responses in Theobroma cacao against Phytophthora palmivora, the causal agent of black rot of the fruit (black pod rot). An in planta greenhouse trial was carried out to determine the reduction of disease symptoms in plants micrografted with three traditional Cuban cacao genotypes of the Trinitario type on UF 677 hybrid rootstocks. The activity of phenylalanine ammonia lyase (PAL) was determined in micrografts of genotype EICB-371. In genotypes EICB-371 and EICB-385, disease severity was significantly reduced in plants pretreated with the bacteria compared to control plants. In contrast, genotype EICB-384 showed no symptom reductions in plants pretreated with the bacterium. PAL enzyme activity was significantly increased in leaves of plants pretreated with CP07 compared to control plants on days 3 and 4 post-inoculation with the pathogen. The results suggest that, depending on the genotype, strain CP07 has potential for protection of T. cacao against P. palmivora in soil substrate and that the interaction of this bacterium with the plant activated defence responses manifested as an increase of PAL activity in leaves.