First, let's not confuse correlation with causation.
Second, I'm convinced that edema, by its own description, does not account for all instances of related symptoms - namely sunken lesions, spotting, and in some cases, exudation of the cytosol (intracellular fluid) . My current theory on the cause of many of these symptoms involves a physiological disorder linked to photosynthesis. Many factors influence that process, soil properties and plant nutrition being no exception. Different soil textures, for example, can affect water relations with a plant. This in turn can affect stomata behavior, gas exchange, and therefore the efficiency of photosynthesis. Another thing that comes to mind: potassium is believed to be instrumental in the process of opening stomata - a potential link between nutrition and photosynthesis. My short answer is that soil properties, via their influence on photosynthesis, can enhance or detract from the severity of the disorder, but I see no root cause. I've seen agave cuttings with no roots and soil produce the same symptoms.
I'd be happy to explain my theory on this subject... but more tests are in order. Unfortunately, winter is the most difficult time to reproduce the symptoms during experiments because I have to battle cooler temperatures.
Matt
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