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An Antifungal Polyacetylene Compound from Phytophthora-infected Safflower. C. A. Thomas, Plant Pathologist, Crops Research Division, ARS, USDA, Beltsville, Maryland 20705; E. H. Allen, Biochemist, Crops Research Division, ARS, USDA, Beltsville, Maryland 20705. Phytopathology 60:261-263. Accepted for publication 5 September 1969. DOI: 10.1094/Phyto-60-261.

A virulent isolate of Phytophthora drechsleri caused necrotic lesions when placed in hypocotyl wounds of 8-week-old Carthamus tinctorius plants. An aqueous solution of the methanol-soluble substances extracted from infected hypocotyls was very inhibitory to mycelial growth of the fungus, whereas similar solutions from healthy hypocotyls were not inhibitory. The inhibitory factor, extractable from the aqueous solution by diethyl ether, was isolated by thin-layer chromatography by using three successive solvent systems. Ultraviolet, infrared, and mass spectral data indicated that the compound is 3,11-tridecadiene-5,7,9-triyne-1,2-diol (safynol). Considering amounts of safynol lost during chromatography, healthy hypocotyls contained 55 µg/100 g fresh tissue. The concentration approximately doubled during 4 days after wounding. A 20-fold increase in concentration occurred in hypocotyls during 4 days after inoculation with P. drechsleri. The median effective dose (ed₅₀) of the compound to inhibit mycelial growth of P. drechsleri was 12 µg/ml. Safynol accounted for as much as 75% of the inhibitory activity of alcohol extracts from infected hypocotyls.