Mesophyll cell collapse can be caused by a number of things, including contact by cold water (which is one reason I heat my greenhouse RO tank). The so-called "microfungus" can also cause it, but its more-common symptom is the silvery sheen the leaves get caused by microscopic pitting of the surface cells.
When it comes to fungal infections, water is often the common denominator, whether it be from being too cold, bad chemistry, allowed to stand, or allowed to splash, carrying a disease from one plant to another.
Something else to keep in mind - and I don't know if it's applicable in this case - but if your culture is lacking something, and it is stressing the plants, it will make them more susceptible to all sorts of disease.
Last edited by Ray; 01-11-2009 at 11:13 AM..
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