Role of Elicitors of Phytoalexin Accumulation in Plant Disease Resistance

Plants are exposed to attack by an immense array of microorganisms, and yet plants are resistant to almost all of these potential pests. Many plant tissues have been observed to respond to an invasion by a pathogenic or nonpathogenic microorganism, whether a fungus, a bacterium or a virus, by accumulating phytoalexins, low molecular weight compounds which inhibit the growth of microorganisms. The production of phytoalexins appears to be a widespread mechanism by which plants attempt to defend themselves against pests ( 1, 2, 3 ). The molecules of microbial origin which trigger phytoalexin accumulation in plants have been called elicitors ( 4 ). Plants recognize and respond to elicitors as foreign molecules. It is highly improbable that plants have evolved separate recognition systems for every bacterial species and strain and every fungal race and every virus that plants are exposed to. Thus, elicitors are likely to be molecules common to many microbes and, in