  Given a unimodular real spherical space $Z=G/H$ we construct for each
boundary degeneration $Z_I=G/H_I$ of $Z$ a Bernstein morphism $B_I:
L^2(Z_I)_{\rm disc }\to L^2(Z)$. We show that $B:=\bigoplus_I B_I$ provides an
isospectral $G$-equivariant morphism onto $L^2(Z)$. Further, the maps $B_I$ are
finite linear combinations of orthogonal projections which translates in the
known cases where $Z$ is a group or a symmetric space into the familiar
Maass-Selberg relations. As a corollary we obtain that $L^2(Z)_{\rm disc }\neq
\emptyset$ provided that ${\mathfrak h}^\perp$ contains elliptic elements in
its interior.
