<Emphasis Type="Italic">Plasmodiophora brassicae</Emphasis> in its Environment |
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Authors: | Geoffrey R Dixon |
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Institution: | (1) Centre for Horticulture & Landscape, School of Biological Sciences, Whiteknights, The University of Reading, Reading, Berkshire, RG6 6AS, UK |
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Abstract: | Plasmodiophora brassicae Wor. is viewed in this article from the standpoint of a highly evolved and successful organism, well fitted for the ecological
niche that it occupies. Physical, chemical, and biological components of the soil environment are discussed in relation to
their effects on the survival, growth, and reproduction of this microbe. It is evident that P. brassicae is well equipped by virtue of its robust resting spores for survival through many seasonal cycles. Germination is probably
triggered as a result of signals initiated by root exudates. The resultant motile zoospore moves rapidly to the root hair
surface and penetration and colonization follow. The short period between germination and penetration is one of greatest vulnerability
for P. brassicae. In this phase survival is affected at the very least by soil texture and structure; its moisture; pH; calcium, boron, and
nitrogen content; and the presence of active microbial antagonists. These factors influence the inoculum potential (sensu Garrett, 1956) and its viability and invasive capacity. There is evidence that these effects may also influence differentially
the survival of some physiologic races of P. brassicae. Considering the interaction of P. brassicae with the soil environment from the perspective of its biological fitness is an unusual approach; most authors consider only
the opportunities to destroy this organism. The approach adopted here is borne of several decades spent studying P. brassicae and the respect that has been engendered for it as a biological entity. This review stops at the point of penetration, although
some of the implications of the environment for successful colonization are included because they form a continuum. Interactions
with the molecular and biochemical cellular environment are considered in other sections in this special edition.
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Keywords: | Plasmodiophora brassicae Clubroot Environment Inoculum potential Biological chemical and physical interactions |
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