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Chemicals are indispensible tools in the continuing effort to minimize crop losses
due to plant diseases. Various active ingredients within fungicides are especially
useful for managing diseases caused by many fungal plant pathogens. Although often
not recognized, various substances formed by plants and present before infection
can enable plants to defend themselves against potential plant pathogens. The level
of defense against potential plant pathogens can range from various levels of resistance
up to outright immunity. A variety of chemical substances are present on the surfaces
of plant parts such as leaves, stems, fruit, seeds and roots. Chemicals with antimicrobial
properties include phenolic compounds, tannins and fatty-acid like materials. Experiments
have shown that some of these compounds have an inhibitory action on certain plant
pathogens. As an example, toxic exudates on leaves of a specific variety of sugar
beet are present at a sufficient concentration to inhibit spore germination of certain
fungal pathogens. Another compound in certain types of tomato plants was shown to
impart resistance to powdery mildew by inhibiting spore germination. Additionally,
proteins and enzymes on plant surfaces can inactivate pathogen enzymes that are
essential for disease development. These preformed compounds, together with various
types of structural plant disease defenses, often drive what we recognize as resistance
to diseases in plants. Even if these plant derived chemical and structural disease
defense systems are not sufficient to totally prevent disease, they along with disease
management tools applied by growers contribute to the overall level of disease suppression
obtained on a particular crop
Plant Disease Defenses
To contact Mike Matheron go to: matheron@ag.arizona.edu.
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For questions or comments on any of the topics please contact Marco Pena at the Yuma Agricultural Center.
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