A Further Investigation of Phytoalexin Formation in the Genus Trifolium
2014
Ingham, John L.
An earlier study of phytoalexin formation in the genus Trifolium has now been extended to include a further 61 species and subspecies. Using the drop-diffusate method, isoflavonoid phytoalexins were isolated from the fungus-inoculated leaflets of 55 accessions, whilst four others produced the stilbene derivative resveratrol. Phytoalexins could not be obtained from the leaflets of two species, T. billardieri and T. grandiflorum. The pterocarpan medicarpin was the most commonly encountered phytoalexin, occurring alone or in various combinations with the known Trifolium isofjavonoids maackiain (pterocarpan), vestitol, isovestitol, sativan, isosativan and arvensan (all isoflavans). Two additional pterocarpans, 4-methoxymedicarpin from T. cherleri and T. pallescens, and 4-hydroxyhomopterocarpin also from T. pallescens, were recognized for the first time as Trifolium phytoalexins. Re-examination of T. aureum re- vealed that this species produced resveratrol as a phytoalexin and not the isoflavan vestitol as previously described.
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