If there is no mycelium/growth then all the one can say is the damage is 'brown' rot. The 'cuboidal cracking' however, is generally larger than found in other brown rots.
Mycelium varies depending on conditions:
a: under dryer conditions - 'silvery-grey' to buff to fawn skin.
Mycelium 'peels' like mushroom.
Many have lilac/yellow patches. Mycelium 'peels' like a mushroom.
b:
under more humid conditions - white cotton wool-like growth.
May be 'tear-drops' present under very wet and humid conditions.
Grey mycelium may be present in cracks in wood.
