  We explore the structure and magnetic field response of edge dislocations in
Grandjean-Cano wedge cells filled with chiral mixtures of the ferroelectric
nematic mesogen DIO. Upon cooling, the ordering changes from paraelectric in
the cholesteric phase N* to antiferroelectric in the smectic SmZ_A* and to
ferroelectric in the cholesteric N_F*. Dislocations of the Burgers vector b
equal the helicoidal pitch P are stable in all three phases, while dislocations
with b=P/2 exist only in the N* and SmZ_A*. The b=P/2 dislocations split into
pairs of {\tau}(-1/2) {\lambda}(+1/2) disclinations, while the thick
dislocations b=P are pairs of nonsingular {\lambda}(-1/2) {\lambda}(+1/2)
disclinations. The polar order makes the {\tau}(-1/2) disclinations unstable in
the N_F* phase, as they should be connected to singular walls in the
polarization field. We propose a model of transformation of the composite
{\tau}(-1/2) line-wall defect into a nonsingular {\lambda}(-1/2) disclination,
which is paired up with a {\lambda}(+1/2) line to form a b=P dislocation. The
SmZ_A* behavior in the in-plane magnetic field is different from that of the
N_F* and N*: the dislocations show no zigzag instability, and the pitch remains
unchanged in the magnetic fields up to 1 T. The behavior is associated with the
finite compressibility of smectic layers.
