An interested web visitor asks:
I have read on numerous occassions that mycorrhizae are very sensitive to soil disturbance. I am
therefore curious as to how mycorrhizae survives as an innoculant. How is it gathered and not killed?
Does the disturbance of isolating, packaging, shipping etc. mycorrhizae not kill the fungi?
Answer: When undisturbed, the mycorrhizal fungi form an interconnected network webbing in the
soil that effectively links all the plants in an area to each other. Nutrients are passed back and forth
within this network according to the needs of individual plants - a very elegant survival strategy, with
the fungi regulating the entire operation.
With tillage, the network is disrupted but the fungi are not destroyed. If seeding is done immediately,
then the hyphae fragments can reestablish mycorrhizae. If the ground lies fallow for some extended
period of time, then the durable mature spores (which can survive hundreds of years, according to
some microbiologists), simply lie dormant in the soil until they receive a signal from the exudate of a
new root nearby. They then activate and attach to the root, starting a new network.
Interestingly, some bacteria that are vitally important in converting soil elements into forms that
plants can use also remain dormant within the fungi spores, in effect ensuring that all the needed
symbiotic partners are present when the time comes to again support a host plant.
For manufacturing inoculant, “nurse plants” are inoculated with a starting culture and allowed to develop
mature spores (which takes from 120-150 days on average). Then the top of the plant is cut off
and the potting mix with all the infected roots and free spores is processed in a way that simulates
the end of a growing season and ground as fine as possible without harming the spores.
It should be noted that the best mycorrhizal inoculants feature a guaranteed count of mature spores,
not simply “propagules” (hyphae fragments which are quicker and cheaper to produce, but not
nearly as durable as the spores).