Biological Activities of Structural Variants of Host-Selective Toxins from Cochliobolus Victoriae

Abstract

There are a number of plant diseases in which specificity is determined by the ability of the pathogen to produce toxins that are selectively active only on susceptible crop cultivars. Twenty to thirty years ago, diseases that involved so called host — selective toxins were considered to be curiosities. However, the long-term and independent efforts of H. Wheeler and R.P. Scheffer and their associates have led to an acceptance of these diseases as relevant models for the elucidation of molecular mechanisms of disease specificity. Genetically, these diseases are the inverse of the gene-for-gene relationship. There is a dominant gene in the pathogen controlling toxin synthesis and a corresponding dominant gene in the host plant that confers sensitivity to the toxin, presumably by coding for a receptor molecule. Thus, characterization of such diseases at the molecular level requires that both the toxin and the receptor, as well as their interaction, be characterized.