Disease resistance chemical factors

Our ENVIRONMENT exposes us daily to a wide variety of xenobiotics in our food, in the air we breathe, or as a result of industrial exposure and toxic wastes. However, despite this exposure, most of us are living long, healthy lives. Certainly individual variation could account for some of the variability in resistance to disease, but other factors are undoubtedly involved. According to a growing body of evidence, diet may be extremely important in increasing resistance to chronic disease. One is tempted to speculate, or hope, that improved dietary habits could improve individual resistance to chemically induced chronic disease. 

Chemical factors are also involved in the resistance of plants to disease and in the competitive ability of a plant to survive within a community of plants. Plant stress may also generate a chemical response giving rise to compounds known as the phytoalexins, the nature of which will depend on the chemistry of the host plant (18, 19). Such response to injury or infection is of great Interest because it has stimulated investigations of the nature of the bloregulatory processes involved. 

The resistance of plants towards disease may well be related to phytoalexin formation, but whatever be the precise function of these compounds, they can only represent one of the complex of factors which operate in disease resistance and immunity. Any protective substances present in the healthy plant must also be important in this connection. A good example of such a substance is provided by our discovery that healthy seedlings of broad bean (Vlcla faba) contain a potent antifungal chemical to which we have given the name Wyerone. 

Development of insects and pathogens is highly dependent on the plant host cultivar. Both physical and physiological host factors influence or limit the life cycle of insects and the disease cycle of pathogens. In fact, the first line of defense against many pathogens is host resistance. Although chemicals are more often used to control insects, host resistance to insects can be very effective (11). 

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