The phytoalexin camalexin is not metabolized by Phoma lingam, Alternaria brassicae, or phytopathogenic bacteria

The metabolism of the cruciferous phytoalexin camalexin by the backleg (Leptosphaeria maculans (Desm.) Ces. et de Not., asexual stage Phoma lingam (Tode ex Fr.) Desm), and blackspot (Alternaria brassicae (Berk.) Sacc.) fungi, as well as the phytopathogenic bacteria Pseudomonas syringae, P. cichorii, Erwinia carotovora, and Xanthomonas campestris was evaluated. The micro-organisms were incubated with camalexin for different time periods and the cultures were extracted and analyzed by high performance liquid chromatography and proton nuclear magnetic resonance. The results of these analyses indicated that camalexin was not metabolized by any of the micro-organisms. Importantly, camalexin appeared to inhibit the production of the phytotoxin destruxin B by A. brassicae, but did not affect the phytotoxins produced by P. lingam. Furthermore, the growth of bacteria and fungi was inhibited almost completely in the presence of camalexin at concentrations greater than or equal to 0.40 mM. (C) 1998 Published by Elsevier Science Ireland Ltd.