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Light and Antifungal Polyacetylene Compounds in Relation to Resistance of Safflower to Phytophthora drechsleri. C. A. Thomas, Plant Pathologist, Plant Science Research Division, ARS, USDA, Beltsville, Maryland 20705; E. H. Allen, Biochemist, Plant Science Research Division, ARS, USDA, Beltsville, Maryland 20705. Phytopathology 61:1459-1461. Accepted for publication 13 July 1971. DOI: 10.1094/Phyto-61-1459.

Six-week-old greenhouse plants of the safflower cultivar Biggs were wound-inoculated in the first inter-node with a virulent isolate of Phytophthora drechsleri. Preinoculation treatments for 72 hr of either continuous light at 1,300 ft-c or continuous darkness immediately prior to inoculation had little effect on the postinoculation reaction. Plants held in controlled-environment rooms with 1,300 ft-c of light for 0, 8, 16, and 24 hr/24 hr period after inoculation were susceptible, moderately susceptible, moderately resistant, and resistant, respectively. 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 with methanol from infected stems 48 hr after inoculation. Subsequently, the compounds were isolated by thin-layer chromatography, using three successive solvent systems. After adjustment for loss during chromatography, infected stems at 0, 8, 16, and 24 hr light/24 hr period contained, respectively, 1,119, 2,233, 2,703, and 3,053 µg safynol, and 13, 94, 251, and 373 µg dehydrosafynol/100 g fresh infected stems. Internodes from adult Biggs plants, wound-inoculated in the first internode with P. megasperma var. sojae (avirulent to safflower) and held in the greenhouse for 4 days, contained 1,500 µg safynol and 750 µg dehydrosafynol/100g fresh infected tissue. These plants were resistant to subsequent infection by P. drechsleri for 4 to 6 days when grown in continuous darkness.

Additional keywords: Carthamus tinctorius, disease resistance.