Biocontrol of Phytophthora root and stem rot disease in papaya (Carica papaya) plants by Photorhabdus, the symbiont bacterium of Heterorhabditis amazonensis

Abstract

The effect of two strains of Photorhabdus spp. from Heterorhabditis amazonensis and their metabolites was tested against Phytophthora in laboratory conditions and in planta using papaya plants. The in vitro experiments showed that both Photorhabdus strains (LPV-499 and LPV-900) have a clear antagonist effect on Phytophthora sp. by suppressing the pathogen growth in more than 62% at 120 h. The bacterial broth was more effective (c.a. 20% better) than the cell free cultures (metabolites) in controlling the oomycete. In planta experiments revealed the biological control potential of both Photorhabdus strains. The most important feature was time of application after pathogen inoculation. During the first two weeks post-infection, bacteria were capable to reduce the pathogenic effect in such a scale that plants recovered up to 89% by curing the necrosis produced in the wounds where the inoculation of the oomycete was done. The number of collapsed stems was reduced to none when the bacteria were applied within the first week post pathogen infection. Agronomic variables such as plant height, fresh and dry weight of stems and roots showed no statistical differences when the curative treatment was applied in the first week post-infection.