Isoflavonoid phytoalexins from the fungus-inoculated leaflets of Erythrina species

Abstract

Using the drop-diffusate technique, a total of 14 isoflavonoid phytoalexins have been variously isolated from the fungus ( Helminthosporium carbonum)-inoculated leaflets of 33 Erythrina species and subspecies. These compounds have been identified as 2′-hydroxydaidzein, genistein and 2′-hydroxygenistein (all isoflavones), 2′-hydroxydihydrodaidzein and dalbergiodin (both isoflavanones), demethylvestitol and isovestitol (both isoflavans), and demethylmedicarpin, glycinol, isomedicarpin, phaseollidin, sandwicarpin, sandwicensin and cristacarpin (all pterocarpans). Diffusates from both control (water-treated) and fungus-inoculated leaflets of E. berenices and E. macrophylla also contained the constitutive isoflavone daidzein. With the exception of daidzein, all the Erythrina isoflavonoids (applied level 25 μg) inhibited the growth of Cladosporium herbarum on silica gel thin-layer plates. The survey data suggest that in terms of its isoflavonoid chemistry, the genus Erythrina has a close affinity with subtribes Diocleinae-Glycininae-Phaseolinae of the tribe Phaseoleae.