Metabolism of the phytoalexins medicarpin and maackiain by Fusarium solani

Non-inhibitory concentrations of the pterocarpan phytoalexin medicarpin were completely metabolized by isolates of Fusarium solani f. sp. pisi, f. sp. cucurbitae, f. sp. phaseoli and two other F. solani isolates genetically related to f. sp. pisi during 24 hr of growth in liquid medium. The major metabolic products accumulated without significant further degradation. Medicarpin was modified at one of three adjacent carbon atoms to form either an isoflavanone derivative, a 1a-hydroxydienone derivative or 6a-hydroxymedicarpin. Whereas each isolate degraded medicarpin to one or more metabolises, the isolates varied as to which metabolise they produced. Maackiain, another pterocarpan phytoalexin, was also metabolized by all the isolates to products analogous to those formed from medicarpin. The ability to metabolize medicarpin and maackiain was not always associated with the ability to metabolize pisatin and phaseollin, two other pterocarpan phytoalexins that were degraded by several of the isolates. Tolerance of medicarpin and maackiain was similarly not always associated with tolerance to pisatin.