agar said:

Certainly, you could use salt free cooked canned corn as a substrate (it is pasteurized - after all). But, in my humble opinion - it would not make a very effective, or productive one.

Rye & WBS work as a substrate. But, they also has significant limitations.

OPTIMAL SUBSTRATE..... should have the form & texture of humus (loam like SPONGY airy mixed organic texture), as well as provide a wide range of essential nutrients.

The limitation of WBS, rye or corn as a substrate is, once it colonizes 100%, it essentially becomes a hard / firm / semi-solid mass of grain & mycelium.

A solid mass of colonized grains only contains so much moisture. That colonized mass doesn't rehydrate well, or quickly. Mushroom fruit bodies are about 90% moisture (water). In order for them to thrive, besides nutrients, they must have an adequate  moisture resource to draw from. Without one, they are restrained far below their optimal growth & fruit size perimeters.

I am not discrediting any grain substrate. They will function, but in my opinion - not in an optimal way.

Something - I wrote in a different life.
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Psilocybe Cubensis are habitat specific. Meaning, they cannot grow in the wild, unless their habitat provides a suitable environment, along with sufficient natural nutrients. Over the millennia, they have evolved inherent genetic traits best suited for their continuous survival in specific geographic area's they successfully inhabit.

All fungi feed by absorption of nutrients. Because of the huge range of potential nutrient sources, fungi evolved enzymes suitable for the specific environments in which they are generally found. The range of enzymes, though wide in may species, is not sufficient for survival in all environments.

Psilocybe Cubensis excrete a complex array of genetically predetermined enzymes for digestion. The enzymes are present in multiple forms, based on a single inherent genetic sequence, and include a range of isoenzymes, which arise from different inherent genetic sequences.

Simply stated, Psilocybe Cubensis excrete enzymes into the organic material in which their underground mycelia (root) system naturally grow. Those enzymes degrade nutrients there, into simple soluble forms of sugars and amino acids, which are then easily absorbed into the mycelia network. Resulting in them acquiring all essential elements with which to grow fruit bodies, and spores (seed) by which they propagate their species.

It is common knowledge that most strains of Psilocybe Cubensis flourish in select warm moist habitats worldwide, associated where horses, cattle and water buffalo naturally spread bovine type manure. Consequently, Psilocybe Cubensis developed inherent genetic traits, enabling then to excrete specific enzymes best suited to enable them to specifically dissolve, digest and take up nutrients available from bovine type manure, and/or soil enriched with it.

Therefore, Psilocybe Cubensis own inherent genetic traits attest that bovine type manure alone, or soils highly enriched with it, is best suited to their nutrient needs, in the wild.

Taking that fact, one step further. Aged leached dry bovine type manure, when aerobically composted together with a small percent of other select fruits, vegetables, grains and straw provides an even more enriched super nutrient source for cultivation of Psilocybe Cubensis . Moreover, a compost of this type provides an ideal moist subsurface habitat (substrate) that, Psilocybe Cubensis mycelia will colonize faster than any other.

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