Induced defense responses in cacao against Phytophthora palmivora (Butler) by Pseudomonas chlororaphis CP07.

Abstract The objective of this study was to evaluate the effect of Pseudomonas chlororaphis CP07, isolated from the rhizosphere of cacao, on the induction of defense responses in Theobroma cacao L. against Phytophthora palmivora (Butler), the causal agent of black rot of the fruit (black pod rot). The 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 levels of phenylalanine ammonia-lyase (PAL) were 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 reduction 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-infection with the pathogen. The results suggested that, depending on the genotype, strain CP07 had potential in the protection of T. cacao against P. palmivora in soil substrate and that the interaction of this bacterium with the benefited plant activated defense responses related to the increase of PAL activity in leaves.