PROPERTIES OF TOXINS OF VERTIGILLIUM DAHLIAE, THE CAUSATIVE AGENT OF COTTON WILT DISEASE

1. Determination of the toxicity of the culture liquid of Verticillium dahliae showed that it contains an active toxin which causes wilting of cotton plant shoots. Thus the fungus produces a toxin which it excretes into the external medium.2. By testing a large number of strains of microorganisms from various taxonomic groups, a test microbe was found which is sensitive to the toxin of Verticillium dahliae.3. Such a sensitive test-microbe made it possible to use chromatography with a bioassay method to select the best solvent for extraction of the toxin.4. The toxin was obtained in concentrated form by extraction with amyl acetate.5. A study of the physico-chemical properties of the toxin showed it to be acidic in nature, and that it has two sharp absorption maxima in the UV region at 245 and 275mμ, and is stable at high temperatures and over a wide range of pH values.6. The toxin of Verticillium dahliae is composed of two fractions, differing in physico-chemical and biological properties.7. The toxin of Verticillium dahliae does not appear to be highly specific, and, besides its marked inhibitory action on cotton, causes wilting of leguminous plants, during which time cereals are not sensitive to the toxin in the concentrations tested.8. The rate of wilting under the influence of the toxin depends on the age and variety of cotton plant. Adult plants wilt more quickly than young plants. The cotton plant variety 108-F (resistant to wilting) is less sensitive to the toxin than variety 2034, which is non-resistant to wilting. The toxin causes browning of the vascular bundles and the surrounding woody parts of the stalk, and the leaves loose their turgidity.9. The tetraene antibiotics, 18-45 and 18-80, produced by actinomycetes, have an effect on the toxin produced by Verticillium dahliae. They interact with the fungal toxin and neutralise its action.10. Treatment of seeds with antibiotics or cultivation in soils which have been enriched with the antibiotic-producing actinomyces produces an immunity in the cotton plants which is passed on to the following generations.