Phenazines producing Pseudomonas isolates decrease Alternaria tenuissima growth, pathogenicity and disease incidence on cardoon

Abstract

Phenazines, secondary metabolites of fluorescent Pseudomonas, represent a group of heterocyclic nitrogen-containing compounds showing a broad spectrum of antibiotic properties. Phenazines producing fluorescent Pseudomonas species are studied extensively for their application in plant disease management. In this study, we examined the antifungal activity of different indigenous Pseudomonas isolates (Q16, B25 and PS2) against the phytopathogenic fungus Alternaria tenuissima, which had infected cardoon (Cynara cardunculus L., Asteraceae). An in vitro experiment demonstrated the antifungal activity of selected indigenous isolates. In addition, an in vivo experiment under gnotobiotic conditions showed suppression of C. cardunculus disease caused by A. tenuissima. The quantification of phenazines revealed significant amounts of phenazine-1-carboxylic acid (PCA) and 2-hydroxy-phenazine-1-carboxylic acid (2-OH-PCA). PCR analysis confirmed the presence of PCA genes in all examined indigenous Pseudomonas isolates. Based on our results, we assume that these Pseudomonas isolates have potential in controlling plant diseases caused by A. tenuissima.