Date of Award:

5-1-1991

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

Abstract

Use of living organisms as a pest control measure is the essence of biocontrol. This study involves evaluation of the potential biocontrol agents for two organisms: a weedy plant species and a fungal plant pathogen. The weed is dyer's woad (Isatis tinctoria) which is rapidly encroaching on all lands in the Intermountain West. The fungal plant pathogen is Phoma betae, a seed- and soilborne pathogen of sugar beets. Puccinia thlaspeos, a native rust pathogen, causes systemic infection on dyer's woad, resulting in severe deformations of stems and leaves and prevention of seed production. It occurs in only a few locations within dyer's woad habitats in Utah and Idaho. Artificial inoculations of dyer's woad in natural stands and experimental fields with a rust spore-talcum mixture resulted in a high proportion of infected plants. The rust's prevention of seed production, its host specificity, its high spore germination rate, and the possibility of artificially introducing it into new areas suggest this pathogen has a potential as a biocontrol agent for dyer's woad. Phoma betae causes a variety of symptoms on mature sugar beet plants, but the most devastating effect is damping-off during seedling emergence. Phoma betae is a seed-transmitted pathogen, and chemical treatment of seeds offers control. However, currently used fungicides provide only partial control. Bacterial antagonists of Phoma could provide protection to developing roots of sugar beet seedlings. Bacteria were isolated from beet seeds and roots. The isolates were screened for their in vitro antagonism against Phoma and another pathogen, one that is soilborne, Rhizoctonia. Other surveyed beneficial properties of the bacterial isolates included HCN and siderophore production, agglutination, and induction of hypersensitive response. Fluorescent pseudomonads, Bacillus, and other unidentified isolates exhibited in vitro antagonism. HCN and siderophore production, as traits associated with antagonism in other systems, were not related to in vitro antagonism exhibited by bacterial isolates in this study.

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