Non-specific Toxins

TLDR: It was claimed by GAumann (1954) that microorganisms are pathogenic only if they are toxigenic; whether or not this proposition agrees with the scientific progress of the last 20 years, depends on the understanding of toxins in plant pathology.

Abstract: It was claimed by GAumann (1954) that microorganisms are pathogenic only if they are toxigenic. Whether or not this proposition agrees with the scientific progress of the last 20 years, depends on our understanding of toxins in plant pathology. In the case of host-specific toxins (see Scheffer in this Volume) their role in the “primary determination of disease” seems obvious. This Chapter, however, deals with the large group of other phytotoxic compounds of plant pathogenic origin which are not host-specific; that is, they are toxic to hosts and non-hosts of the pathogen. Since these toxins cannot explain host specificity they have been defined as “secondary determinants of disease”. Nevertheless, some of these toxins seem to be necessary for a successful infection of the host plant, whereas others play only a secondary role. It is one aim of this review to compilate the available data from non-host-specific toxins in regard to their possible role in disease. Therefore, the main emphasis is placed on plant physiological and plant pathological aspects, contained in the subchapters “Mode of action of phytotoxic compounds” (see Section 8) and “Toxins in relation to pathogenesis” (see Section 9). Also the “Chemistry of phytotoxic compounds” (see Section 7) is reviewed as far as possible, since the chemical characterization can contribute to an understanding of the physiological role of a toxin.