I’m in the midst of studying. One thing lingering over my head has been definitions of a few basic words relating to plant pathology. I mentioned my struggles with this in a post last week. Today I finally settled on my definitions of plant disease and pathogen.
Plant Disease: Adverse changes in plant form or function in response to the influence of one or more enabled pathogens.
It’s elegant isn’t it? I spent hours developing it. Each word went through careful consideration. Right now I think it is the best possible definition of plant disease. I’m rather excited about the word “enabled.” I did not find this in any other definitions of disease, but it seems to me to be a key element. I feel like I just built a better mousetrap.
My definition of pathogen is critical to explaining my disease definition.
Pathogen: An agent capable of inciting or inflicting disease.
I like the simplicity here. Once again I used a word (“inflicting”) I have not seen in previous definitions. The reason I feel the need to add inflict is that I am choosing to make no stipulation about a pathogen being living or non-living. This means that anything that causes plant disease (reduced form or function) is a pathogen. Bugs. Bacteria. Water. Humans. Lawnmowers. Fungi. Nutrients. Wind. And the list goes on. Some pathogens incite changes in plant physiology (like a nutrient toxicity); some pathogens inflict physical damage (like a hungry herbivore).
One thing that caused me much duress was the issue of deficiency. When a plant becomes diseased as a response to the lack of something, it that thing then a pathogen? For instance, if a plant does not have enough nitrogen its function and form will be changed adversely. Does this make nitrogen a pathogen? I say yes. I call it culpability in absentia. The question is, what is causing the adverse change in form and function? It’s nitrogen. Nitrogen is needed for proteins, amino acids, nucleotides, coenzymes, nucleic acids, some hormones, and chlorophyll. When it is lacking bad things happen. Add nitrogen and the problem is solved.
Life is dynamic. We live in a world that is full of stresses, pathogens, and challenges. I’m inclined to say every living thing is diseased on some level. When you have a tree that is dying it is likely not the result of one pathogen, but an interaction of pathogens. Or it might be one pathogen that has been enabled by a particular set of factors (environmental conditions, host physiology or morphology, presence of a vector, etc).
I feel much better now that I have definitions of plant disease and pathogen prepared to defend. I’m hoping they still look as good to me tomorrow as they do today. May this peace of mind linger.
I need to get back to my books. If you managed to read this entire post you deserve a gold star.