Agrobacterium radiobacter strain K84: a model biocontrol system
1990
Farrand, S.K.
Agrobacterium radiobacter strain K84 is used in many parts of the world to control crown gall disease. Two characteristics of strain K84, production of agrocin 84 and root colonization, are primary determinants for successful control exhibited by this organism. Production of agrocin 84 is encoded on a self-conjugal plasmid. Where pathogenic agrobacteria are sensitive to agrocin 84, control is usually very good. However, where soil forms are resistant, strain K84 is generally ineffective. Sensitivity to agrocin 84 is highly specific and is associated with the Ti plasmid present in the pathogenic agrobacteria. Loss of sensitivity is associated with mutations on the Ti plasmid or with acquisition of the agrocin 84 plasmid by the pathogen. This suggests ways in which the system can be modified. To protect against genetic dissemination of the agrocin plasmid to tumorigenic strains a Tra- deletion mutant has been constructed. This strain no longer transfers the plasmid but still controls crown gall. To broaden the range of strain K84, derivatives are being constructed that produce other agrocins of various specificities.
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