A few years ago, I had the opportunity to observe an experiment that consisted of transplanting tomatoes into large pots containing pure beach sand - unwashed and quite salty.
Each of the dozen or so groups of test plants had been inoculated with a different type of endomycorrhizal fungi - Glomus mosseae, G. intraradices, G. aggregatum, Gigaspora margarita, etc.
Very quickly it became obvious that the beach sand was a less than ideal potting medium. The non-inoculated control plants died almost immediately, followed by most of the test plants. Some test group plants survived, but were weak in appearance and bore only a few small fruits.
However, one group of test plants all thrived and produced good crops of large tomatoes. That one particular fungi, and only that one, had the ability to help its host plants deal with the extreme low-fertility/salty growing conditions.
The moral of this? With more than 150 named types of AM fungi, plus countless local adaptations that have evolved, be very skeptical of the projectability of any testing that involves only one or two types. Just because one beneficial fungus does not perform well in a lab test does not mean those results are typical of all types.
I would speculate that AM fungi that have evolved in the harshest soil and climate situations will prove to be most useful for growing crops in poor soils, and hope that researchers will devote some time to identifying, capturing, and trialing such types.
Yes, it is more convenient to conduct tests using only commonly available types, but I'm guessing that the greatest rewards will not show up there.
Cheers, my friends,
President, BioOrganics, Inc.