The Sterol Requirement of Phytophthora Cactorum

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Abstract
Several sterols and related substances were tested for ability to promote sexual reproduction in P. cactorum. These compounds were classified as active (oospores formed), partially active (oogonia and antheridia formed, but no oospores), or inactive (no oogonia). Quantitative differences among active substances were noted in respect to the numbers of oospores produced and the time of their appearance. The most active substances tested were 29-isofucosterol and [beta]-sitosterol. Loss of activity was associated with shortening of the side chain of the sterol molecule or change in its configuration, absence of a double bond in the B ring or of a hydroxyl group at position 3 on the A ring.