Accumulation of isoflavonoid phytoalexins in leaves of Arachis hypogaea differing in reaction to rust ( Puccinia arachidis ) and early leafspot ( Cercospora arachidicola )

Groundnut leaves, naturally infected in the field with Cercospora arachidicola or artificially infected in the greenhouse with C. arachidicola or Puccinia arachidis , accumulated isoflavonoid phytoalexins. Major compounds included medicarpin, formononetin, demethylmedicarpin, three isoflavanones and the isoflavone, daidzein. In both greenhouse and field experiments cv. Egret was less susceptible than cv. P84/5/244 to both pathogens, and accumulated phytoalexin (medicarpin) concentrations which were up to three times greater. Higher concentrations and greater variation of phytoalexins were detected when both cultivars were infected with C. arachidicola than when they were infected with P. arachidis.