  We study the in-plane resistivity anisotropy in the spin-glass phase of the
high-$T_{c}$ cuprates, on the basis of holes moving in a spiral spin
background. This picture follows from analysis of the extended $t-J$ model with
Coulomb impurities. In the variable-range hopping regime the resistivity
anisotropy is found to have a maximum value of around 90%, and it decreases
with temperature, in excellent agreement with experiments in
La$_{2-x}$Sr$_x$CuO$_4$. In our approach the transport anisotropy is due to the
non-collinearity of the spiral spin state, rather than an intrinsic tendency of
the charges to self-organize.
