MYKE is the brand name of a product that is essentially beneficial, symbiotic mycorrhizal fungi. The fungi naturally occur in soils - they colonize the roots of plants and give the plants nutrients and water in exchange for sugars from the plants. Established plants would likely already have been colonized by the fungi in the soil. Using MYKE with new plantings helps speed up the coloniztion process and it would be particularly valuable in poor soils where the natural fungi may not be present or present in low levels. I have been using it now for two years and it does appear to help get things off to a faster start so I now use it every time I plant something.
The company tha makes it is Canadian. You might be interested in the information on the MYKE web site at: