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Relationship of Safynol and Dehydrosafynol Accumulation to Phytophthora Resistance in 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 62:471-474. Accepted for publication 10 November 1971. DOI: 10.1094/Phyto-62-471.

Six-week-old safflower plants of the breeding line Biggs and the variety Nebraska-10 were wound-inoculated in the first internode with Phytophthora drechsleri (virulent to Nebraska-10, avirulent to Biggs) and P. megasperma var. sojae (avirulent to both). Plants were held at 30 C with 2,200 ft-c of continuous light. Two antifungal polyacetylenes, safynol (trans-trans-3,11-tridecadiene-5, 7, 9-triyne-1, 2 - diol), and dehydrosafynol (trans-11-tridecene-3,5,7,9-tetrayne-1,2-diol), were extracted from infected stems and quantitated. When inoculated with P. drechsleri, Biggs stems (resistant) contained 956 µg (12 hr) and 1,472 µg (24 hr) safynol, and 47 µg (12 hr) and 297 µg (24 hr) dehydrosafynol/100 g fresh wt. Nebraska-10 (susceptible), inoculated with P. drechsleri, contained 943 µg (12 hr) and 1,590 µg (24 hr) safynol, and 27 µg (12 hr) and 200 µg (24 hr) dehydrosafynol/100 g fresh wt. When inoculated with P. megasperma var. sojae, the cultivars had similar safynol contents. Biggs and Nebraska-10 stems, inoculated with P. megasperma var. sojae, contained, respectively, 128 µg (12 hr) and 382 µg (24 hr), and 57 µg (12 hr) and 228 µg (24 hr) dehydrosafynol/100 g fresh wt. The rate of accumulation of dehydrosafynol was statistically correlated with the high disease resistance of Biggs. Nebraska-10 plants, 4 days after inoculation with P. megasperma var. sojae, contained 2,100 µg safynol and 876 µg dehydrosafynol/100 g fresh wt, and were resistant to P. drechsleri for 2 to 4 days. Safynol and dehydrosafynol were, respectively, 1.5 and 13.5 times more toxic to P. megasperma var. sojae than to P. drechsleri.