Phytotoxin Production by Verticillium albo-atrum Reinke et Berthold

Abstract

THE physiology of vascular wilt diseases caused by Fusarium and Verticillium species has received considerable attention during recent years^1–4. Of these organisms, less work has been carried out on Verticillium, and certain aspects of the disease syndrome caused by this fungus are not fully understood. Studies on symptom initiation have for the most part been concerned with the production by the fungus of pectolytic enzymes^5–11. Numerous authors have mentioned the possible role of toxins in disease initiation, but little supporting experimental evidence has so far been produced. Moreover, from the lack of a precise definition, the toxins of some authors^12,13 might include extracellular pectolytic enzymes. Porter and Green¹⁴ and Green¹⁵ published the first authentic accounts of toxins produced in Verticillium culture filtrates. Bio-assay of nearly all suspected disease-inducing agencies has been on cut shoots, in an attempt to simulate wilt conditions, in the naturally infected plant. In Nature, however, wilting symptoms usually develop after about 14 days, and experiments in this laboratory have shown that, in the case of seedling infection, growth inhibition rather than overall wilting is a more valid symptom of disease. Up to five weeks after infection in these plants wilting is a gradual basipetal desiccation while the leaf area of apparently turgid leaves is reduced by 80 per cent. This symptom is quite different from the general collapse of turgor common in mature infected plants and may be independent of it.