Specificity — An Assessment
In the context of plant pathology the study of specificity deals with why a pathogen grows and causes disease in some cells and tissues of plants but not in others. When these cells and tissues are in the same plant we have the tissue and organ specificity described by Graniti of which there are many striking examples. There are also the marked differences in reaction to a pathogen that occur in what seem to be similar cells sometimes close together in the same tissue. Mesothetic reactions to rust fungi are special examples of such differences. It is surprising that they have not been more studied in view of their implications for hypotheses on mechanisms of interactions believed to be controlled by gene-for-gene relations. They and other ce11-from-ce11 differences would be difficult to analyse because of their unpredictability but this is not true of tissue and organ specificity with predictable responses and where differences in reaction can be as striking as in resistant and susceptible plants. Here, presumably, factors related to the position of cells over-ride those that control reactions in plants of different genotype. Similar considerations apply to factors such as temperature that alter the response of plants of a given genotype.
KeywordsResistant Plant Susceptible Plant Specialized Pathogen Rust Fungus Wide Host Range
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