  It has been recently proved that the automorphism group of a minimal subshift
with non-superlinear word complexity is virtually $\mathbb{Z}$ [DDPM15, CK15].
In this article we extend this result to a broader class proving that the
automorphism group of a minimal S-adic subshift of finite alphabet rank is
virtually $\mathbb{Z}$. The proof is based on a fine combinatorial analysis of
the asymptotic classes in this type of subshifts, which we prove are a finite
number.
