Plants can resist invasion by many potential pathogens, but just how is this accomplished? One approach is through the use of physical defense methods. Just as our skin provides a physical barrier preventing movement of microbes into our bodies, the cuticle or surface covering on plants serves the same function. Many plant pathogens must adhere to the plant surface for a given time in order to penetrate into the plant and cause infection. This ability to colonize plants may be disrupted by the amount of wax present and the quality of the cuticle that covers plants. Waxes prevent the formation of a film of water on plants, which is essential for deposition and growth of bacterial and fungal pathogens on plants. Abundant plant hairs can perform a similar water repellency function. Cuticle thickness and toughness of epidermal cell walls play an important role in the resistance of plants to several pathogens. However, this form of disease resistance can be circumvented by wounds. Also, many pathogenic bacteria and fungi enter plants only through stomata or other natural openings. The structure and size of these openings can greatly affect the ability of some pathogens to invade plants. The physical plant attributes present before exposure to potential plant pathogens play an important role in a plant’s ability to resist many pathogens and the diseases they cause. Without the presence of these physical barriers, plants in general would be susceptible to infection by many more plant pathogens.

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To contact Mike Matheron go to: matheron@ag.arizona.edu.

For questions or comments on any of the topics please contact Marco Pena at the Yuma Agricultural Center.
College of Agriculture, The University of Arizona, Tucson, AZ.