Date of Award:

5-1-1988

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Department name when degree awarded

Biology

Committee Chair(s)

Anne J. Anderson

Committee

Anne J. Anderson

Committee

Sherman V. Thompson

Committee

Dennis L. Welker

Abstract

Pseudomonas putida is a soil saprophyte that suppresses certain fungal root pathogens. The bacterium is an aggressive colonizer of plant root surfaces and the bacterial cells are agglutinated by a root surface glycoprotein, termed an agglutinin. To study the relationship between agglutination and root surface colonization, mutants of P. putida were derived which demonstrated enhanced or decreased agglutinability. In short-term binding studies, non-agglutinability. In short-term binding studies, non-agglutinable (Agg-) mutants obtained by ethyl-methanesulfonate mutagenesis adhered to sterile bean seedling roots at levels 10-15 fold less than parental cells. Tn5-Agg- mutants adhered at levels comparable to that of parental cells. Both Tn5 and EMS Agg- mutants were released more readily in comparison to the parental cells upon shaking the intact root in water. No increased release of Agg- cells was observed upon exposure of water- washed roots to EDTA, whereas this treatment enhanced further release of Agg+ cells. The super-agglutinable (AggS) mutants behaved like the Agg+ parent. The ability of P. putida isolates to colonize plant root surfaces was studied using roots grown from inoculated seeds under aseptic conditions. Parental Agg+ P. putida colonized the root surfaces. Agg- EMS and Tn5 mutants also colonized the root surfaces but at levels lower than the Agg+ parental strain. One of the two AggS mutants behaved like the parent, whereas antoher AggS mutant colonized at a reduced level. P. putida (Agg+) caused suppression of Fusarium wilt in cucumber plants grown in field absence of added Fusarium inoculum. Agg- and AggS mutants had different effects than the Agg+ parent. These mutants did not enhance plant growth to the level observed with parental isolate and offered less protection against the Fusarium pathogen than the parent. Cucumber roots were colonzied by mutants (Agg- and AggS) to a lesser extent than the parental type. Fusarium oxysporum f. sp. phaseoli and P. putida were able to grow on components present in washes from bean roots.

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