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Fire blight protection with avirulent mutants of Erwinia amylovora

Jacqueline Laurent^2,

ENSH-ENITHP, Laboratoire de Pathologie Végétale, 2 rue Le NoCtre, F-49045 Angers, France
Laboratoire de Pathologie Végétale, INRA, 16, rue Claude Bernard, F-75231 Paris Cedex 05, France
Station de Pathologie Végétale, INRA, Beaucouze, F-49070 Angers, France

⁴Author for correspondence: Michel Tharaud. Tel: +33 2 41 22 54 38. Fax: +33 2 -2 22 54 59.

ABSTRACT

Fire blight is a necrotic disease caused by the bacterium Erwinia amyiovora, which affects pears, apples and ornamentals including Crataegus, Pyracantha, and Cotoneaster. The disease can be only partially controlled, through the use of resistant genotypes, cultural measures and antibacterial compounds, thus other methods must be investigated. It has long been established that avirulent isolates of the pathogen can control the disease, under experimental conditions. However, field use of avirulent isolates is not acceptable because of their unknown genetic stability. The protective ability under controlled conditions of genetically characterized avirulent insertion mutants of E. amylovora was examined. A bioassay on apple seedlings was used for the determination of the protective ability of 34 insertion mutants (hrp, dsp, ams). Some protective effect could be observed with most of the mutants tested and was dependent on the avirulent/virulent inoculum ratio as well as on the level of virulence of the pathogen; a minimal concentration of the avirulent mutant was necessary to give a significant level of protection. An early competition between avirulent and virulent strains for putative infection sites might be involved. For six of the mutants tested, the protective ability was particularly high and might be related to the alteration of regulatory functions of hrp genes. Results obtained with Ams^- and Ams^- Hrp^- mutants suggested that the bacterial exopolysaccharide might play a role in the protection.

Present address: Biology Cellulaire, University Paris-Sud, Bat. 444, F-91405 Orsay Cedex, France.

This article has been cited by other articles:

				E. L. Schnabel and A. L. Jones Isolation and Characterization of Five Erwinia amylovora Bacteriophages and Assessment of Phage Resistance in Strains of Erwinia amylovora Appl. Envir. Microbiol., January 1, 2001; 67(1): 59 - 64. [Abstract] [Full Text]