In vitro antifungal activity of brassinin, camalexin and two isothiocyanates against the crucifer pathogens Alternaria brassicicola and Alternaria brassicae

In vitro assays investigated the responses of Alternaria brassicicola and A. brassicae isolates towards two crucifer phytoalexins and two isothiocyanates (ITC) by evaluating their potential toxic effects on different fungal growth parameters. Although variable responses towards each compound was observed within the species A. brassicicola, the results obtained confirmed the antifungal effects of camalexin, brassinin, allyl- (AlITC) and benzyl- (BzITC) isothiocyanates, at different developmental stages of both Alternaria species. Irrespective of the tested isolate, the phytoalexin camalexin exhibited the greater inhibitory effect with mean EC₅₀ values ranging from 34 μ m (germ-tube elongation) to 183 μ m (mycelial growth). Germ-tube elongation was more sensitive compared to conidial germination and mycelial growth, with mean EC₅₀ values of the former of 81 μ m, 520 μ m and 870 μ m for brassinin, BzITC and AlITC, respectively.