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https://hdl.handle.net/2142/22675
Description
Title
Molecular systematics of Plasmodiophora brassicae
Author(s)
Castlebury, Lisa Ann
Issue Date
1994
Doctoral Committee Chair(s)
Domier, Leslie L.
Department of Study
Plant Biology
Discipline
Plant Biology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Molecular
Biology, Botany
Agriculture, Plant Pathology
Language
eng
Abstract
The molecular systematics of Plasmodiophora brassicae Woronin, the causal agent of clubroot in crucifers were investigated using the small subunit ribosomal RNA gene sequence. Plasmodiophoromycetes, a group of obligate parasites of various higher plants, algae and Oomycetes have been classified in various ways as both protists and fungi. It is not known which, if any, of these classification schemes reflects the actual evolutionary relationships of this group.
A rapid and effective technique for inoculating Chinese cabbage (Brassica pekinensis Rupr.) roots with Plasmodiophora brassicae was developed. The method described consists of placing thin slices of P. brassicae infected root tissue next to the roots of 14-day-old seedlings. A method for purifying P. brassicae resting spores from macerated infected Brassica pekinensis (Chinese cabbage) roots was also developed. This method consists of a series of centrifugations in 50% sucrose and distilled water to remove most of the plant root debris and centrifugation of resting spores in a continuous gradient of LUDOX (40% silica suspension-DuPont)/deionized water.
Nucleic acids were extracted from Plasmodiophora brassicae resting spores. The ssrRNA genes were amplified using the polymerase chain reaction (PCR), producing an approximately 3 kilobase (kb) DNA fragment, and sequenced. The ssrRNA genes were determined to contain 3 group I introns. The sequence of the PCR product was aligned with representatives of the major eukaryotic lineages. This alignment was analyzed by fastDNAml, PAUP, and neighbor-joining. Results indicate that P. brassicae is not closely related to any of the organisms with which it has been classified in the past. The maximum likelihood phylogenetic analysis suggests that P. brassicae has a relationship with the ciliated protists as suggested by Barr based on the similarity of the mechanism for root penetration in P. brassicae to trichocysts in ciliates and on similarities in the flagellar rootlet system.
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