  Vishik's antidynamo theorem is applied to non-stretched twisted magnetic flux
tube in Riemannian space. Marginal or slow dynamos along curved (folded),
torsioned (twisted) and non-stretching flux tubes plasma flows are obtained}.
Riemannian curvature of twisted magnetic flux tube is computed in terms of the
Frenet curvature in the thin tube limit. It is shown that, for non-stretched
filaments fast dynamo action in diffusive case cannot be obtained, in agreement
with Vishik's argument, that fast dynamo cannot be obtained in non-stretched
flows. \textbf{In this case a non-uniform stretching slow dynamo is
obtained}.\textbf{An example is given which generalizes plasma dynamo laminar
flows, recently presented by Wang et al [Phys Plasmas (2002)], in the case of
low magnetic Reynolds number $Re_{m}\ge{210}$. Curved and twisting Riemannian
heliotrons, where non-dynamo modes are found even when stretching is presented,
shows that the simple presence of stretching is not enough for the existence of
dynamo action. Folding is equivalent to Riemann curvature and can be used to
cancell magnetic fields, not enhancing the dynamo action. In this case
non-dynamo modes are found for certain values of torsion or Frenet curvature
(folding) in the spirit of anti-dynamo theorem. It is shown that curvature and
stretching are fundamental for the existence of fast dynamos in plasmas.
