My first guess (without much information and without pictures) would have been the beginning of roots. Cuttings often develop "white dots" before normal/recognizable roots develop.

Another guess (again, without much information and without pictures) could be some kind of fungus (not mycorrhizal).

This is probably not the best forum for this type of issue, and, without more information and pictures, it's a shot in the dark, at best. You'd be better off posting in the propagation forum with pictures and any further relevant information you might have.