Control of rust diseases by diterpenes from Nicotiana glutinosa

Abstract

AN epimeric mixture of the diterpenes sclareol and 13-epi-sclareol (sclareol) (Fig. 1) has been shown to constitute 10%; of the surface exudate on leaves of Nicotiana glutinosa¹. Investigations into its effect on fungal growth showed that it neither inhibits the spore germination of several species of facultative pathogens in vitro nor reduces the weight of mycelium produced in liquid medium. The development of hyphae of certain species of fungi, for example Alternaria brassicicola, is, however, markedly affected by this compound. In the presence of sclareol, increased branching is induced which leads to a substantial reduction in the diameter of colonies growing on agar¹. Such morphological effects could be interpreted as the result of alterations in the regulation of natural fungal growth processes. This report describes the effect of sclareol on the germination and growth of rust fungi in vitro, and the protection it can provide to plants against diseases caused by these fungi.