Pathogen resistance mechanisms plant

Selective toxicity is also important in relation to the development of resistance or tolerance to pollutants from two distinct points of view. On the one hand, there is interest among scientists concerned with crop protection and disease control in mechanisms by which crop pests, vectors of disease, plant pathogens, and weeds develop resistance to pesticides. Understanding the mechanism should point to ways of overcoming resistance, for example, other compounds not affected by resistance mechanisms or synergists to inhibit enzymes that provide a resistance mechanism. On the other hand, the development of resistance can be a useful indication of the environmental impact of pollutants. 

Immunization of Plants by Attenuated Forms of Pathogens. As has been argued by Kuc and Caruso (47), plants can be immunized to achieve higher levels of resistance to pathogens. Similar mechanisms may conceivably provide a line of defense against phytophagous insects without the challenge-independent accumulation of defensive compounds. 

Resistant of plant pathogens to antibiotics Tolerance or resistance of pathogenic microorganisms to antibiotics has occurred shortly after application of antibiotics for the control of plant diseases as shown in Table VI. In order to reduce or avoid the emergence of tolerant fungi and bacteria in the fields, the alternate or combined application of chemicals with different mechanisms of action is recommended. 

They act as antipathogenic agents and thus affect the process of pathogenesis. They may act on the host through the Induction of plant resistance mechanisms such as stimulation of lignification or enhancement of phytoalexin production. (Please refer to the chapter by Salt and Kuc in this volume for further discussion of this type of compound.) They may act on the pathogen to accentuate elicitor release or to prevent infection (host penetration), colonization (inhibition of phytotoxin synthesis, extracellular enzyme production and action, or phytoalexin degradation) or reproduction. 

Compounds that affect Host Reactions. Examples of compounds which enhance or induce host reactions to pathogens include 2,2-dichloro-3,3-dimethyl-cyclopropane carboxylic acid (DDCC), probenazole, and fosetyl-Al (4). Although these chemicals do not stop the fungus from penetrating the plant, they are quite effective at preventing colonization through the enhancement of the host s resistance mechanisms. Further studies are needed to elucidate how these resistance mechanisms are triggered. 

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