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A Second Antifungal Polyacetylene Compound from Phytophthora-Infected Safflower. Edward H. Allen, Biochemist, Plant Science Research Division, ARS, USDA, Beltsville, Maryland 20705; Charles A. Thomas, Plant Pathologist, Plant Science Research Division, ARS, USDA, Beltsville, Maryland 20705. Phytopathology 61:1107-1109. Accepted for publication 20 April 1971. DOI: 10.1094/Phyto-61-1107.

Six-week-old plants of the safflower cultivar Biggs (Carthamus tinctorius) were wound-inoculated in the first internode with a virulent isolate of Phytophthora drechsleri. An aqueous solution of the methanol soluble substances, extracted from infected stems 48 hr after inoculation, was partitioned with diethyl ether. Two highly antifungal factors in the ether phase were isolated by thin-layer chromatography. One of the antifungal compounds was identified as the previously reported polyacetylene, trans-trans-3,11-tridecadiene-5,7,9-triyne-1,2-diol (safynol). Ultraviolet, infrared, mass, and nuclear magnetic resonance spectral data indicated that the second highly antifungal compound is trans-11-tridecene-3,5,7,9,-tetrayne-1,2-diol (dehydrosafynol). Adjusted for loss during chromatography, the amount of these compounds in infected stems 48 hr after inoculation was 296 µg dehydrosafynol and 3,370 µg safynol/100 g fresh-infected stems. Healthy stems contained less than 0.2 µg dehydrosafynol and 83 µg safynol/100 g fresh wt. The median effective dose (ed₅₀) of dehydrosafynol required to inhibit mycelial growth of P. drechsleri was 1.7 µg/ml. Both antifungal compounds were found in high concentration in tissues exterior to the vascular ring.