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United States Department of Agriculture

Agricultural Research Service

Research Project: DETECTION, SOURCE IDENTIFICATION, ENVIRONMENTAL TRANSPORT, FATE, AND TREATMENT OF PATHOGENIC MICROORGANISMS DERIVED FROM ANIMAL WASTES Title: An assessment of environmental conditions for control of downy brome by Pseudomonas fluorescens D7

item Ibekwe, Abasiofiok
item Kennedy, Ann
item Stubbs, Tami - WASH ST U, PULLMAN,WA

Submitted to: International Journal of Environmental Technology and Management(IJETM)
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 1, 2009
Publication Date: February 1, 2010
Repository URL:
Citation: Ibekwe, A.M., Kennedy, A.C., Stubbs, T. 2010. An assessment of environmental conditions for control of downy brome by Pseudomonas fluorescens D7. International Journal of Environmental Technology and Management(IJETM). 12:27-46.

Interpretive Summary: The use of bacteria as biological control agents for the purpose of controlling weed growth gained recognition in recent years. However, the effectiveness of this approach is very low in the field. Many laboratory studies have shown 75 to 95 percent effectiveness of bacteria for the control of weed germination and growth. In this study, a non-pathogenic Pseudomonas fluorescens Strain D7 was used. In the field, this strain plays a beneficial role as a biological control agent with benign interaction with wheat roots and inhibitory effects on downy brome roots. Different mutants of Pseudomonas fluorescens Strain D7 were tested under different environmental conditions to determine the effect of temperature, pH, and moisture conditions on D7 growth and inhibition of downy brome. The important genes responsible for toxin production and the inhibitory activities on downy brome were identified. Our results showed that several genes were involved in the production of toxin and these genes were responsible for the different physical characteristic observed in the bacteria.

Technical Abstract: Purpose: We evaluated the conditions that favoured Pseudomonas fluorescens strain D7 (P.f. D7) growth and inhibition of downy brome. Design/methodology/approach: Tn5 mutagenesis and a competitive assay were used to isolate mutants of P.f. D7. Isolates were screened for polysaccharide production and toxin response. Seven mutants were tested under varying pH, temperature and water potential and characterised using Random Amplified Polymorphic DNA analysis. Findings: Temperature, pH, and water potential did not affect weed suppression in bioassays, except at 37°C and with NaCl. Originality and/value: Understanding the genetics of P.f. D7 will help in the development of successful weed biocontrol systems.

Last Modified: 3/30/2015
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