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Applied and Environmental Microbiology, October 1998, p. 3977-3982, Vol. 64, No. 10
School of Biological Sciences,
Received 26 September 1997/Accepted 29 July 1998
The biological control strain Agrobacterium rhizogenes
K84 is an effective agent in the control of Agrobacterium
pathogens, the causative agents of crown gall disease. A number of
factors are thought to play a role in the control process, including
production of the specific agrocins 84 and 434, which differ in the
spectra of pathogenic strains that they inhibit in vitro. A range of
derivatives of strain K84 has been developed with every
combination of the three resident plasmids, pAgK84, pAgK434,
and pAtK84b, including a plasmid-free strain. These
derivatives produced either both, one, or neither of the characterized
agrocins 84 and 434 and were isolated by plasmid curing, conjugation,
and Tn5 transposon mutagenesis. The ability of the
derivative strains to inhibit gall formation on almond roots was
compared to that of the wild-type K84 parent. Treatment with the
plasmid-free derivative did not result in a significant level
of control of an A. rhizogenes pathogen based on numbers or
dry weight of galls formed on injured almond roots. The presence of
plasmid pAgK84, pAgK434, or pAtK84b significantly enhanced the
biological control efficacy of K84 derivatives, and the highest level
of control was observed with strains harboring two or more plasmids.
The results observed with strains deficient in agrocin 434 production
suggest that this product may play an important role in the biological
control of A. rhizogenes pathogens. The involvement of
plasmid pAgK84b in biological control has not previously been reported.
This study supports the conclusion that multiple factors are involved
in the success of strain K84 as a biological control agent.
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Construction of a Range of Derivatives of the Biological Control
Strain Agrobacterium rhizogenes K84: a Study of Factors
Involved in Biological Control of Crown Gall Disease
and
*
Corresponding author. Mailing address: School of
Biological Sciences, Flinders University of South Australia, GPO Box
2100, Adelaide 5001, South Australia. Phone: 61-8-82013930. Fax: 61-8-82013015. E-mail:
btncm{at}cc.flinders.edu.au.
Present address: Environmental Engineering Dept., Environmental
College, Tehran University, Tehran, Iran.
Applied and Environmental Microbiology, October 1998, p. 3977-3982, Vol. 64, No. 10
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
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