Relative importance of motility and antibiosis in the rhizoplane competence of a biocontrol agent Pseudomonas fluorescens MelRC2Rif |
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Authors: | K Toyota K Ikeda |
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Institution: | (1) Laboratory of Soil Biology and Chemistry, School of Agricultural Sciences, Nagoya University, Nagoya 464-01, Japan Tel: +81 (52) 789 5323; Fax: +81 (52) 789 4012; e-mail: ktoyota@nuagr1.agr.nagoya-u.ac.jp, JP |
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Abstract: | Mutants defective in motility or antibiotics production were obtained by Tn5 mutagenesis of a biocontrol agent Pseudomonas fluorescens MelRC2Rif (wt). Tomato or melon seeds were co-inoculated with a Tn5 mutant and wt in a 1:1 ratio and then grown in soil for
10 days. There was no change in ratios of Tn5 mutants defective in antibiosis to wt in the process of rhizoplane colonization,
suggesting little contribution of in vitro antibiosis to the rhizoplane competence of P. fluorescens MelRC2Rif. Similar results were also obtained when seeds treated with bacteria were planted in soil artificially infested
with fungal pathogens. In contrast, ratios of Tn5 mutants defective in motility to wt significantly decreased, suggesting
the contribution of motility to the rhizoplane competence of this bacterium. When a non-motile Tn5 mutant and wt were co-inoculated
into soil at a matric potential of pF 2.3 (–20 kPa) and plants were then grown, there was no change in the ratio in rhizoplane
colonization, suggesting that motility might have a role in the movement along roots but an insignificant role in the movement
from bulk soil towards roots. When they were co-inoculated into 0.2% water agar (WA) instead of soil, a remarkable decline
in ratios was detected. Thus it was soil structure that hindered the efficiency of motility. Time course enumeration of rhizoplane
colonization of tomatoes grown in WA revealed that motility was an important means of movement towards and/or along roots
rather than the multiplication on roots.
Received: 8 July 1996 |
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Keywords: | Pseudomonas fluorescens MelRC2Rif Motility Antibiosis Rhizosphere |
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