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.