There are three types of mycorrhizal fungi inoculants commercially available endo, ecto and ericoid. Most are available in dry form. Ecto is in spore form and endo is available as propagules, i.e., spores, root fragments and hyphae. Endo in spore form alone is a poor inoculant if you want results within 6 weeks according to research that has been published. Research has shown that endo mycorrhizal inoculants with spores, root fragments and hyphae are superior to those containing only spores. Research shows that hyphal fragments are most infective, followed by mycorrhizal root fragments and then spores. Root fragments actually contain many spores and are better at protecting spores from adverse environmental conditions compared to spores alone. Ericoid is presently is in dry form.
Reasons why spores alone are dangerous for an inoculant:
1. Spores degrade over time, even when dried
2. For some species, spores are the only infective propagules and when they degrade the inocula are effectively dead.
3. For many species in Glomus, hyphae from root fragments can be up to 10X more infective than spores.
4. Root fragments, when dried, are not as susceptible to degradation as spores, especially in a formulation containing high organic matter.
5. Ergo (from 4 above), even if part of the inoculum degrades with storage, infective propagules still can be present for a longer period in a mixed inoculum formulation.
The reality of inoculum marketers today is that most are just that "marketers". Some sell a single strain of mycorrhiza mixed in with a carrier backed with all the claims thousands of research studies will support. Some sell liquids. Some sell powders. Some sell only one kind. Some sell tablets. Most sell "cocktails" containing a variety of organisms. Some have formulated for numbers. Some for results.
One company that has been in the industry for 10 years marketed a transplant product for trees and shrubs which contained no beneficial bacteria package. What were they thinking not to include such an obvious package. Most landscape materials are planted in disturbed soils. What logic is there in not including a bacteria package? Bacillus subtilla, for example, is an effective "mycorrhiza helper bacteria".
Diversity is THE name of the game. The ground beneath our feet is a macrocosm of hundreds of systems and billions of participants. Diversity - include as many natural organisms and systems as feasible - that's the signature of a manufacturer that understands their correct role. Ingredients that support a clear biological advantage to support plant growth in logical amounts and and at appropriate times.