Toxicity of cotton phytoalexins to zoopathogenic fungi.

The sesquiterpenoid phytoalexins desoxyhemigossypol, desoxymethoxyhemigossypol, and hemigossypolone formed in cotton (Gossypium hirsutum and G. barbadense) stem xylem infected with Verticillium dahliae were shown to be highly toxic to zoopathogenic fungi. This appears to be the first study of the toxicity of terpenoid phytoalexins to zoopathogenic fungi. The toxicities of the phytoalexins expressed as MIC (micrograms ml-1) values were 8 to 128 against four isolates of Candida albicans and one isolate of Cryptococcus neoformans. These highly toxic compounds or their derivatives may prove useful for the treatment of animal mycoses.

Histochemical localization of desoxyhemigossypol, a phytoalexin in Verticillium dahliae-infected cotton stems.

The terpenoid phytoalexin desoxyhemigossypol (dHG) was detected histochemically in the stem xyiem of Verticillium dahliae Kleb-infected, wilt-resistant Seabrook Sea Island cotton as a green product on V. dahliae mycelium within vessel lumens and in specialized, often solitary, paravascular parenchyma cells. The SbCl3 -HClO4 histochemical reagent yielded a green-coloured Sb-dHG product specific for dHG when used as a spray on chromatograms of extracts from Verticillium-infected stele tissue. Both dHG and related terpenoid aldehyde derivatives occurred together in parenchyma cells and on V. dahliae mycelium. The presence of dHG on Verticillium mycelium reinforces previous studies that identified dHG as the most toxic and possibly most important phytoalexin in the resistance of cotton to V. dahliae.