The Relevance of Non-Host-Specific Toxins in the Expression of Virulence by Pathogens

Abstract

The interaction between the pathogen and the plant is complex, and the present state of our knowledge about this interplay is fragmentary. Our ultimate goal should be to define plant pathogenesis at the molecular level, not only in terms of altered plant biochemistry but also in terms of the pathogen's biochemistry , its alteration in the plant environment, and its function within the plant environ­ ment as time progresses. Studies using chemically defined toxins provide a powerful tool and a useful starting point for these objectives. An understanding of the relevance of toxins to the expression of virulence by plant pathogenic microorganisms has been slow to develop. This has been largely because many of the earlier investigations pertaining to the biological activity of toxins proceeded without an understanding of the chemistry in­ volved, or of the necessity for chemical purity. Chemical studies of toxins have in fact only gained impetus in recent years, so that now several precisely defined chemical compounds of microbial origin are known to be associated with the diseases caused by a number of bacteria and fungi. It is only since this advance in our chemical knowledge that we have been able to move on to meaningful examinations of the biological significance and function of toxins in plant-pathogen interactions.