Plant disease resistance

By Mike Matheron, UA Extension Plant Pathologist

Plants can be resistant to many potential pathogens, but just how is this resistance accomplished? One method is the use of physical defense.

Just as our skin provides a physical barrier preventing movement of microbes into the body, the cuticle or surface covering on plants serves the same function. Many plant pathogens must adhere to the plant surface for a given time 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 the 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.

This form of disease resistance can be circumvented by wounds. Many pathogenic bacteria and fungi enter plants only through stomata or other natural openings. The structure and size of the openings can greatly affect the ability of some pathogens to invade plants. These physical plant attributes, that are present before exposure to potential plant pathogens, play an important role in the plant’s ability to resist many diseases.

Without the presence of these physical barriers, plants in general would be susceptible to infection by many more plant pathogens than they are now.

Contact Matheron: (928) 726-6856 or matheron@ag.arizona.edu.