A reassessment of the role of steroidal alkaloids in the physiology of Phytophthora

Phytophthora cactorum was incubated in vitro with solasodine, [³H] solanidine, and [³H] solanine in the presence and absence of an equal weight of [¹⁴C] cholesterol. The extent to which the two genins and the glycoalkaloid inhibited sterol-induced sexual reproduction was dependent primarily on the extent to which the fungus assimilated the steroidal alkaloids. Cholesterol increased the uptake of solasodine and [³H] solanidine by the mycelium, but the genins affected neither cholesterol-induced growth responses, measured as radial diameter or dry wt, nor the accumulation of [¹⁴C] cholesterol, nor its conversion to esters and glycosides. The genins were not converted to esters or glycosides, but [³H] solanine was hydrolysed to solanidine. Solanine was not significantly assimilated by the fungus.