The most basic goal of mycorrhizal inoculation is to introduce any type of the beneficial fungi spores to plant roots. The nature of these fungi is to deliver nutrients and moisture to their host plants, and they can be an extremely useful tool for growers.
A much more sophisticated goal would be to introduce specific types of mycorrhizal spores that represent the best possible match with a grower's specific plants in specific fields. But which of the more than 150 (so far) named types of the fungi will be the best for a given situation? Which of those types will give maximum benefit to a individual grower's crops or ornamental plants? Which will help his or her plants thrive with the very least amounts of fertilizer and water, or produce the greatest yields? And where does a grower go to buy the best of the 150+ types?
Hard to say. I'm not aware of any wide-scale research being done to evaluate the effects of matching all the various fungi types to various plants in various soils in various climates (with millions of possible combinations). For most fungi types, there are simply not enough of their spores being propagated to conduct extensive trials even if someone wanted to.
A fundamental question that also remains largely unanswered is whether these fungi are more plant-specific or soil-specific. In other words, will a particular fungus make a powerful match with, say, tomato plants anywhere they are planted? Or will that same fungus match up strongly with nearly any plant in, say, sandy desert-type soils but not do anything worthwhile elsewhere?
We need to recognize that these are expensive questions to answer. It's hard to see any entity except the government undertaking such research, and I suspect that the USDA's prevailing soil-chemistry orientation would make it hard to obtain funding for any large biological studies.
Five soil scientists will have at least six opinions on this sort of issue, but it seems there is a leaning toward regarding fungi types as being more soil-specific. Fungi apparently interconnect all plants in a given area, creating what has been called a food web. I hasten to mention that there are plant-specific fungi, given nature's unique arrangements. Orchids are one such example.
At the moment, our industry's best answer to the above described areas of uncertainty is to include multiple types of widely-adapted spores in inoculants - a "shotgun" approach, if you will. Our widest range landscape product (LA) contains the spores of eight Endo and seven Ecto types. This pretty much ensures that at least one will work for nearly any planting situation, but it would be more efficient if we could better target the types - employ more of a "rifle" approach.
I think if I were beginning college again instead of banging up against retirement age, I'd set out to learn as much as I could about how to use the many types of mycorrhizal fungi on crop plants. I bet I could somehow find ways of profitably using that knowledge in the future.
Cheers, my friends,
Don Chapman
President, BioOrganics, Inc.