Ethylene production and toxigenicity of methionine and its derivatives with riboflavin in cultures of Verticillium, Fusarium and Colletotrichum species exposed to light

Ethylene was produced by Verticillium dahliae Kleb. grown in liquid Czapek's medium. The rate of ethylene production was enhanced by light but was not affected by shaking or the growth rate of the cultures. L-, D- and DL-methionine, DL-ethionine and a -keto- y -methylthiobutyric acid (KMBA) were good substrates for ethylene production. KMBA may be an intermediate in ethylene production and it appears to be degraded to ethylene either enzymatically by peroxidase or photochemically in the presence of riboflavin. Addition of riboflavin or briefly heating the cultures to 100°C enhanced ethylene production greatly, while the addition of sodium azide, potassium cyanide and catalase were very inhibitory. The SS4 (non-defoliating) pathotype of V. dahliae produced significantly more ethylene (up to 108.4 nl ethylene h₁ from 20 ml-10-day-old cultures) than did the T9 (defoliating) pathotype with all substrates tested. The results suggest that the in vitro rate of ethylene production is not related to the relative virulence of pathotypes of V. dahliae on cotton. A number of Verticillium species, Fusarium oxysporum f. sp. vasinfectum and Colletotrichum dematium var. truncatum were able to produce ethylene in liquid Czapek's medium containing 1 m M L-methionine under continuous light. Riboflavin, although highly stimulatory to ethylene production, caused a fungicidal reaction to all the fungi tested in Czapek's medium containing L-methionine under continuous light. The fungicidal effect of the riboflavin-methionine-light combination occurred at concentrations of riboflavin and methionine less than 1.33 μ M and 0.5 m M , respectively. No fungicidal activity was detected when the cultures were grown in total darkness or when either methionine or riboflavin was omitted from the culture medium.