The effect in vitro of exogenously applied p-hydroxybenzoic acid on Fusarium oxysporum f. sp. Niveum

The allelochemical, p-hydroxybenzoic acid, was applied in vitro to Fusarium oxysporum f. sp. niveum, a pathogen causing watermelon wilt disease, by adding the acid to the medium. P-hydroxybenzoic acid slightly stimulated the growth of the fungus at low concentrations (200–800 mg L-1), but it strongly inhibited its growth at the highest concentration (1600 mg L-1). At this acid concentration the mycelial mass was reduced by 63.7% and the conidial germination rate was decreased by 46.9–100%. Sporulation was also suppressed, with a 91.4% reduction. However, fusaric acid production by Fusarium oxysporum f. sp. niveum was stimulated with an increase of 47.3–379.4%. The activity of proteinase, pectinase and cellulase was stimulated by p-hydroxybenzoic acid, but amylase activity was depressed.