  We discuss the radial spectrum of light scalar mesons in the framework of
spectral sum rules in the large-Nc (planar) limit of QCD. Two methods based on
the use of linear radial Regge trajectories are presented. A special emphasis
is placed on the appearance of scalar isoscalar state near 0.5 GeV. Within the
considered sum rules, the existence of this meson (which could be a large-Nc
counterpart to the sigma-meson) is closely related with existence of resonances
in the vector channels and on the radial scalar trajectory.
