BIOCONTROL OF ROOT ROT OF STRAWBERRY CAUSED BY PHYTOPHTHORA CACTORUM WITH A COMBINATION OF TWO PSEUDOMONAS FLUORESCENS STRAINS
L. Agustí, A. Bonaterra, C. Moragrega, J. Camps, E. Montesinos
Pseudomonas fluorescens strains EPS817 and EPS894 protecting strawberry plants against Phytophthora cactorum root rot and producing different bioactive metabolites were used in combination to enhance the level of biocontrol achieved by each strain used alone. Moreover, it was confirmed by chemical analysis that the strains have clear physiological differences in terms of biocontrol potential. EPS817 produced 2,4-diacetylphloroglucinol and HCN, and EPS894 produced phenazine-1-carboxylic acid and pyoluteorin. Interaction studies between bacterial strains and P. cactorum revealed a significant inhibition of cyst germination in vitro. Scanning electron microscopy confirmed that each strain inhibited P. cactorum cyst germination on the strawberry root surface. Bacterial strains were able to colonize and survive on strawberry roots individually and together in a substrate potting mixture, thus indicating compatibility between strains. Biocontrol experiments performed in strawberry potted plants under greenhouse conditions revealed that the mixture of both strains not only reduced the disease severity of Phytophthora root rot but also the variability within experiments compared to single strain application.