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Stimulation of Spore Germination of Thielaviopsis basicola by Fatty Acids from Rhizosphere Soil. G. C. Papavizas, Microbiologist, Plant Science Research Division, ARS, USDA, Beltsville, Maryland 20705; M. F. Kovacs, Jr., Chemist, Plant Science Research Division, ARS, USDA, Beltsville, Maryland 20705. Phytopathology 62:688-694. Accepted for publication 26 January 1972. DOI: 10.1094/Phyto-62-688.

No fatty acids (C16 to C18) were detected from bean roots after 8 days of growth in aseptic liquid cultures, but plants grown in sand-solution cultures released 0.60, 0.48, and 0.55 µg/plant palmitic acid, stearic acid, and oleic acid, respectively. Total fatty acids were 1 to 2 times higher in extracts of rhizosphere soil than in extracts of nonrhizosphere soil. The total amount of unsaturated fatty acids (linoleic, oleic, palmitoleic) in extracts of soil from the rhizosphere of 6-, 14-, and 21-day-old bean plants exceeded that of extracts from nonrhizosphere soil. Endoconidia and chlamydospores of Thielaviopsis basicola did not germinate in nonamended control soil. Considerable germination occurred in bean rhizosphere soil and in nonrhizosphere soil fortified with hexane extracts of rhizosphere soil. Rhizosphere soil extracts from susceptible hosts of T. basicola (bean, cotton, tobacco) had more fatty acids than extracts from nonhost plants (corn, wheat, kale); yet corn and wheat rhizosphere soil extracts stimulated chlamydospore germination. Extracts from soil amended with alfalfa hay contained 1 to 2 times more fatty acids than extracts of nonamended soil during the first 4 days after hay incorporation. Extracts from alfalfa-amended soil stimulated spore germination.

Additional keywords: fungistasis, black root rot, exudation.