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Effect of Pseudomonas putida on the Stimulation of Pythium ultimum by Seed Volatiles of Pea and Soybean. T. C. Paulitz, Department of Plant Science, Macdonald College of McGill University, Ste. Anne de Bellevue, Quebec, H9X 1C0, Canada; Phytopathology 81:1282-1287. Accepted for publication 24 April 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/Phyto-81-1282.

Pseudomonas putida strain N1R increased the emergence of soybean and pea in soil infested with Pythium ultimum when applied to the seeds as a cell suspension. Hyphal growth from soil-produced sporangia of P. ultimum was stimulated by volatiles from germinating seeds of pea and soybean, and the stimulation was reduced when the seeds were treated with N1R. Ethanol and acetaldehyde (10 ?1/L) also stimulated hyphal growth from P. ultimum soil inoculum. Treatment of seeds with N1R reduced the concentration of ethanol and acetaldehyde produced by germinating pea and soybean during the 24 h period after imbibition. N1R used ethanol as a sole carbon source in culture, completely metabolizing 15500 ?l/L within 48 h. Ethanol use was partially inhibited by glucose, but was detected even at 1,000 ?g/ml glucose. N1R may reduce damping-off by competing for and using volatile exudates from germinating pea and soybean seeds. These volatile seed exudates may serve both inductive and nutritional functions in the pathogenesis of Pythium damping-off disease.