Pseudomonas chlororaphis CP07 strain reduces disease severity caused by Phytophthora palmivora in genotypes of Theobroma cacao

Black pod rot is the most important disease affecting Theobroma cacao in Cuba. Plant growth promoting bacteria (PGPB) are considered an alternative for controlling plant disease in the context of the integrated management. The present work was aimed to evaluate Pseudomonas chlororaphis strain CP07, isolated from T. cacao rhizosphere, as potential PGPB against P. palmivora in cacao plants cultivated under controlled conditions. Three genotypes of Cuban traditional cacao of the group Trinitario and the genotype UF 677 were used. The effect of CP07 was evaluated by using detached leaf tests and in planta assays with plants obtained in vitro from both seeds and micrografting. Inoculation of P. palmivora in control plants showed that genotypes EICB-371, EICB-384 and UF 677 were highly susceptible to the disease (71.4 to 99% disease severity) while EICB-385 was significantly less susceptible (39 to 54.5%). In EICB-371 and EICB-385 genotypes, disease symptoms were significantly reduced in presence of CP07 compared to the control plants in all assays. In contrast, for EICB-384 and UF 677 genotypes, there was not reduction of disease severity in plants pre-treated with CP07. Results show the protective effect of treating cacao plants with CP07 against P. palmivora . Plant genotype significantly influenced the protective ability of bacteria affecting the CP07-mediated disease control. Results suggest that depending on cacao genotype, CP07 has a potential for inducing plant defense against P. palmivora which can be used in the control of black pod rot.