  We study one-loop corrections in scalar and gauge field theories on the
non-commutative torus. For rational theta, Morita equivalence allows these
theories to be reformulated in terms of ordinary theories on a commutative
torus with twisted boundary conditions. UV/IR mixing does not lead to
singularities, however there can be large corrections. In particular, gauge
theories show tachyonic instabilities for some of the modes. We discuss their
relevance to spontaneous Z_N x Z_N symmetry breaking in the Morita dual SU(N)
theory due to electric flux condensation.
