Phytoalexin induction as a new dynamic approach to the study of systematic relationships among higher plants

Abstract

IT is well established that many higher plants respond to microbial invasion by the de novo production of organic substances called phytoalexins1,2. These compounds are absent from healthy plants and are induced by the attacking microorganisms. Although the role of phytoalexins in disease resistance is not yet entirely clear, considerable evidence suggests that they are of importance in the protection of higher plants from fungal colonisation. Although few surveys have been attempted, there is clearly a taxonomic element in phytoalexin biosynthesis, in that different plant families accumulate chemically different types of compounds3. Thus, the Leguminosae in general produce isoflavonoids, the Solanaceae diterpenes, the Compositae polyacetylenes and so on2; anomalies are rare, for example, the furanoacetylene, wyerone acid, from Vicia faba (Leguminosae)4. As lesser variations also occur within these families, there is the clear possibility of using phytoalexin induction as a tool in taxonomic studies. We report here the first successful application of this technique to the problems of classification at the generic and species level in the Leguminosae.