11 How pathogens adapt to host defenses - Copy

11 How pathogens adapt to host defenses - Copy - PP 315...

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PP 315 / 590J  Lecture 11 How pathogens adapt to host defenses Pathogenicity/virulence/aggressiveness vs Partial and complete resistance We've talked about the  resistance-susceptibility continuum  on a number of occasions this semester. I  also introduced several terms that describe types of host resistance. Let's first look at these terms in a  little more detail. complete resistance  - prevents growth and reproduction of the pathogen such that pathogen populations  decline sharply; this type of resistance places strong selection pressure on the pathogen to adapt  (change) or die. This strong selection pressure frequently results in changes in the pathogen known as  races ( virulence ). partial resistance  - resistance that is not complete and results in a range of resistance responses from  low to high. This type of resistance does not place strong selection pressure on the pathogen, but it does  put selection pressure to become more  aggressive  on the new resistant varieties.  (There is some data  that indicates that partial resistance selects for virulence in some pathogens) If we look at terms that refer to properties or characteristics of the pathogen, the following three terms are  most frequently used: pathogenicity -  the ability to cause disease virulence  - (specific virulence) - pathogenicity characterized by specific genetic interactions between  genotypes of the pathogen and genotypes of the host. Occurrence of  races  in the pathogen is the result.  (a qualitative trait) This type of reaction is the result of complete resistance genes placed in host cultivars. aggressiveness -  level of disease caused by the pathogen (a quantitative trait). The level of  aggressiveness may change in response to host genotypes that have higher or perhaps lower levels of  partial resistance. Host-pathogen specificity and the gene-for-gene hypothesis.   The basis for understanding the  genetic nature of resistance began with the work of Biffen in 1905 when he reported that resistance to rust of wheat caused by  Puccinia striformis  was inherited as a single-
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This note was uploaded on 03/22/2008 for the course PP 315 taught by Professor Shew during the Spring '08 term at N.C. State.

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11 How pathogens adapt to host defenses - Copy - PP 315...

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