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Plant Immunity

Sean Cawley
Latest posts by Sean Cawley (see all)

Ever wonder why some plants seem to remain healthy and vibrant while others seem to get eaten up by insects or “catch” other diseases?

All organisms have an immune system designed to protect them from diseases and to detect and respond to pathogens that try to invade from the environment. We know about our own immune system with its lymphatic system, white cells, antibodies, spleen, and gut microbiome. We can enhance our immune system by eating well, being physically active, getting enough sleep, etc.

But what about plants? They have evolved many mechanisms to detect and defend against numerous pathogenic attacks, such as avoiding growth during time periods when pathogens are plentiful, producing a biochemical response to a pathogen, and cell tissue death at the site of invasion (so the pathogen is arrested within the dead plant tissue). Protection against herbivores can include thorns, thick cell walls, producing chemicals that are toxic to insects or animals trying to eat them, etc.

As gardeners, we know that photosynthesis converts carbon, oxygen and nitrogen into the various sugars (carbohydrates) and fats (lipids) that are plants’ building blocks. Equally important are micro-nutrients and water that are drawn into the plant from its roots to further supply the necessary chemicals to create the defense system to ward off disease and insect attacks.

The soil is vastly important in supporting the plant’s defense system. “Soil is a living ecosystem that includes minerals, air, water, and habitat for creatures plus the creatures themselves…Did you know that soil provides 14 of 17 essential plant nutrients?” (OSU EM 9304, 12/2020)

Soil, with all of its micro-organisms, fungi, and bacteria creates a symbiotic relationship with the plants. Some of the carbohydrates and lipids produced by the plants find their way to the roots and share their bounty with these micro-organisms. In exchange, soil’s micro-organisms allow water and trace minerals to be readily absorbed by the plant root system and carried up into the plant. The plants need the water and these nutrients to generate both growth and defense chemicals. And both plants and pathogenic organisms are constantly evolving to “outwit” the other for survival.

So, when you are out in your garden and witness your plant in stress or looking lackluster, or there are unusual looking spots or insects chowing down on a leaf, remember to first ask – how is the soil? Is it healthy? Remember that the soil supports the immune system of the plant. To learn more about this magnificent symbiotic relationship, you may be interested in the video, books and papers listed below.



  • Groundwork: A Family Journey into Regenerative Cotton. 16-minute video about a family that applied regenerative agriculture practices to restore the health of their soil. Click here to watch the video.


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