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Influence of Infection by Phytophthora drechsleri on Inhibitory Materials in Resistant and Susceptible Safflower Hypocotyls. Lowell B. Johnson, Former Assistant Research Plant Pathologist, Department of Plant Pathology, University of California, Davis, Present address: Department of Plant Pathology, Kansas State University, Manhattan 66502. Phytopathology 60:1000-1004. Accepted for publication 27 January 1970. DOI: 10.1094/Phyto-60-1000.

Resistant Biggs safflower (Carthamus tinctorius) hypocotyls stab-inoculated with Phytophthora drechsleri mycelium showed a greater susceptibility around inoculation wounds flushed with water by string wicks than did inoculated controls without wicks, suggesting that a fungistatic material might have been removed in the water. Extracts of inoculated Biggs hypocotyls were generally less inhibitory, however, than extracts from inoculated susceptible Nebraska 10 (N10) safflower, and no positive evidence was obtained for a phytoalexin. Hypocotyl exudates, obtained by spotting the cut ends of hypocotyls directly on silica-gel thin-layer sheets, were chromatographed in carbon tetrachloride or hexane. One spot which fluoresced red under ultraviolet was generally larger on chromatograms of Biggs exudates spotted 24 hr after inoculation than with inoculated N10 exudates. Ethyl acetate extracts showed little difference between resistant and susceptible inoculated hypocotyls in the amount of this substance. The solubility of the substance, its apparent polymerization under ultraviolet light, and its ultraviolet and infrared spectra all indicated that it was a polyacetylene, though its exact structure was not determined. Preliminary assays indicated that the substance was inhibitory to zoospore germination and to a lesser extent to mycelial growth of P. drechsleri. The physiologic significance of the increase of this substance is uncertain, but the substance appears different from others previously reported to increase in plant tissues with disease development.