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Applied and Environmental Microbiology, July 2008, p. 4285-4291, Vol. 74, No. 14
0099-2240/08/$08.00+0     doi:10.1128/AEM.00263-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Differential Interference with Pythium ultimum Sporangial Activation and Germination by Enterobacter cloacae in the Corn and Cucumber Spermospheres{triangledown}

Sofia Windstam{dagger} and Eric B. Nelson*

Cornell University, Department of Plant Pathology and Plant-Microbe Biology, 334 Plant Science Building, Ithaca, New York 14853

Received 30 January 2008/ Accepted 21 May 2008

Differential protection of plants by Enterobacter cloacae was studied by investigating early sensing and response behavior of Pythium ultimum sporangia toward seeds in the presence or absence of E. cloacae. Ten percent of P. ultimum sporangia were activated within the first 30 min of exposure to cucumber seeds. In contrast, 44% of the sporangia were activated as early as 15 min after exposure to corn seeds with over 80% sporangial activation by 30 min. Germ tubes emerged from sporangia after 2.5 and 1.0 h in the cucumber and corn spermospheres, respectively. Seed application of the wild-type strain of E. cloacae (EcCT-501R3) reduced sporangial activation by 45% in the cucumber spermosphere, whereas no reduction was observed in the corn spermosphere. Fatty acid transport and degradation mutants of E. cloacae (strains EcL1 and Ec31, respectively) did not reduce sporangial activation in either of the spermospheres. Although wild-type or mutant strains of E. cloacae failed to reduce seed colonization incidence, pathogen biomass on cucumber seeds was reduced in the presence of E. cloacae strains EcCT-501R3 and Ec31 by 4 and 8 h after sowing, respectively. By 12 h, levels of P. ultimum on cucumber seeds treated with E. cloacae EcCT-501R3 did not differ from levels on noninoculated seeds. On corn seeds, P. ultimum biomass was not affected by the presence of any E. cloacae strain. When introduced after sporangial activation had occurred, E. cloacae failed to reduce P. ultimum biomass on cucumber seeds compared with that on nontreated seeds. Also, increasing numbers of sporangia used to inoculate seeds yielded increased pathogen biomass at each sampling time. This indicates a direct link between the level of seed-colonizing biomass of P. ultimum and the number of activated and germinated sporangia in the spermosphere, suggesting that E. cloacae suppresses P. ultimum seed infections by reducing sporangial activation and germination within the first 30 to 90 min after sowing.

* Corresponding author. Mailing address: Cornell University, Department of Plant Pathology, 334 Plant Science Building, Ithaca, NY 14853. Phone: (607) 255-7841. Fax: (607) 254-6448. E-mail: ebn1{at}cornell.edu

{triangledown} Published ahead of print on 30 May 2008.

{dagger} Present address: Michigan State University, Department of Plant Pathology, 140 Plant Biology Building, East Lansing, MI 48824.

Applied and Environmental Microbiology, July 2008, p. 4285-4291, Vol. 74, No. 14
0099-2240/08/$08.00+0     doi:10.1128/AEM.00263-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Windstam, S., Nelson, E. B. (2008). Temporal Release of Fatty Acids and Sugars in the Spermosphere: Impacts on Enterobacter cloacae-Induced Biological Control. Appl. Environ. Microbiol. 74: 4292-4299 [Abstract] [Full Text]  


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