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Rapid Germination of Sporangia of Pythium Species in Response to Volatiles from Germinating Seeds. Eric B. Nelson, Assistant professor, Department of Plant Pathology, University of Arkansas, Fayetteville 72701, Present address: Department of Plant Pathology, Cornell University, Ithaca, NY 14853; Phytopathology 77:1108-1112. Accepted for publication 9 February 1987. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-1108.

Sporangia of Pythium ultimum, P. sylvaticum, and P. irregulare germinated in response to volatile seed exudates. Germination was most rapid at 25 C with germ tubes evident 2 hr after exposure. Maximum germination occurred within 68 hr. Germination was delayed at 15 C but suppressed at 35 C even though sporangia were 100% germinable. Volatiles evolved during seed germination were separated by gas chromatography, identified, and quantified. Acetaldehyde and ethanol were the only components detected after 2 hr of imbibition, whereas ethane, acetone, and methanol were also detected after 6 hr of imbibition. Ethane production was detected only from seeds germinated at 15 C. Levels of all other volatiles increased as imbibition temperature increased. Acetaldehyde was not stimulatory to sporangium germination at concentrations of 16,200 nmol/ml. Ethanol was stimulatory only at concentrations of 17 nmol/ml, whereas higher concentrations appeared to be inhibitory.