Phytoalexins: What have we learned after 60 years?

One of the best and longest-studied defense response of plants to infection is the induced accumulation of antimicrobial, low-molecular-weight seconda ry metabolites known as phytoalexins. Since the phytoalexin hypothesis was first proposed in 1940, a role for these compounds in defense has been reve aled through several experimental approaches. Support has come, for example , through studies on the rate of phytoalexins in relation to cessation of p athogen development, quantification of phytoalexins at the infection site, and relationship of pathogen virulence to the phytoalexin tolerance. Eviden ce in support of phytoalexins in resistance as well some recent advances in phytoalexin biosynthesis are reviewed. Criteria for evaluating a role for phytoalexins in disease resistance are also discussed.