Insights on the susceptibility of plant pathogenic fungi to phenazine-1-carboxylic acid and its chemical derivatives

Pseudomonas chlororaphis subsp. aureofaciens strain M71 produced two phenazine compounds as main secondary metabolites. These metabolites were identified as phenazine-1-carboxylic acid (PCA) and 2-hydroxyphenazine (2-OH P). In this study, the spectrum of the activity of PCA and 2-OH P was evaluated against a group of crop and forestal plant pathogenic fungi by an agar plate bioassay. PCA was active against most of the tested plant pathogens, while 2-OH P slightly inhibited a few fungal species. Furthermore, four semisynthesised derivatives of PCA (phenazine-1-carboxymethyl, phenazine-1-carboxamide, phenazine-1-hydroxymethyl and phenazine-1-acetoxymethyl) were assayed for their antifungal activity against 11 phytopathogenic species. Results showed that the carboxyl group is a structural feature important for the antifungal activity of PCA. Since the activity of phenazine-1-carboxymethyl and phenazine-1-carboxamide, the two more lipophilic and reversible PCA derivatives remained substantially unaltered compared with PCA.