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The influence of motility of rhizobium leguminosarum biovar trifolii TA1 on the colonization and nodulation of roots of trifolium subterraneum cv. Mt. Barker

Parco, Socorro Z. (1993) The influence of motility of rhizobium leguminosarum biovar trifolii TA1 on the colonization and nodulation of roots of trifolium subterraneum cv. Mt. Barker. Masters by Research thesis, Murdoch University.

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Abstract

The significance of motility for root colonisation and nodulation was investigated by comparing the behaviour of well-characterised motile (MNF 1000) and non-motile (MNF 1005) strains of Rhizobium leguminosarum bv. trifolii. A very small volume (5 pi) was used to inoculate clover (Trifolium subtcrrancum cv. Mt. Barker) roots to avoid mass flow of organisms. The nodulation pattern was used as an index of the colonisation of the roots; it was assessed by a grid-sectioning technique which divided the soil column into 1 cm cubes, or by gamma-ray computer assisted tomography (CAT) scanning. Direct rhizosphere counts were used as an alternative way of determining root colonisation.

From equal inocula, the motile strain produced more nodules than the nonmotile. Grid-sectioning showed that the motile strain produced nodules at distances further from the inoculation point than the non-motile mutant. However, the technique suffered from the distortion of root aiH nodule distribution caused by the introduction of the sectioning plate.

Attempts were made to use CAT scanning as a non-destructive, nondistorting technique to generate a three-dimensional picture of nodule distribution in the soil columns. Although some 70% of the known nodules corresponded to areas of low density in the scans, the technique currently lacks sufficient resolution.

When the root nodule bacteria were located on the roots by direct counting, the motile strain was found along the whole of the tap root, while the non-motile mutant was essentially confined to a small zone at the inoculation point, rhizosphere counts indicated a much greater spread of the motile strain than did The measurement of the nodule distribution.

In steam-treated soil, both nodulation and rhizosphere counts indicate that the motile strain colonised the clover root system much more extensively than did the non-motile strain.

Item Type: Thesis (Masters by Research)
Murdoch Affiliation: School of Biological and Environmental Sciences
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: repository@murdoch.edu.au. Thank you.
Supervisor(s): Dilworth, Michael and Glenn, Andrew
URI: http://researchrepository.murdoch.edu.au/id/eprint/51939
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