Date of Award:

5-1985

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Plants, Soils, and Climate

Committee Chair(s)

Neal Van Alfen

Committee

Neal Van Alfen

Committee

Jon Takemoto

Committee

Jim Hoffmann

Committee

Sherm Thomson

Abstract

Corynebacterium michiganense pv insidiosum, the organism responsible for bacterial wilt of alfalfa, produces an extracellular polysaccharide (EPS) that has been linked to its virulence. The EPS is composed of three different-sized molecules (components I, II and III). It has been demonstrated that this EPS accumulates in the vascular system of infected plants and causes disruption of the flow of water.

The importance of EPS to the survival and pathogenicity of C.m. pv insidiosumis not known. In order to begin assessing the value of EPS, mutant strains that are EPS-deficient were isolated after UV mutagenisis. Analysis by gel filtration and gas chromatography showed four types of EPS mutants. Type 1 was reduced in all three EPS components and showed significant shifts in sugar composition. Type 2 did not produce the largest EPS component and also had a sugar composition different from that of the wild type. No component II, the medium-sized molecule, was produced by the Type 3 mutant and both components I and II were missing from Type 4. Sugar composition of the last types was stable as compared to that of wild type.

Alfalfa seedling inoculations with the wild type and mutant strains gave no indication of virulence. Mutant strains were able to grow within host tissue and retain their EPS-deficient characteristics.

It was concluded that large amounts of EPS are not necessary for the growth and survival of C.m. pv insidiosum within host tissue. Also, no correlation was found between EPS composition and cell growth.

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