  We consider the ratio of the cross section of production of heavy
bottom-antibottom pairs ($\sigma_{b\bar b}$) to the cross section of production
of top-antitop pairs ($\sigma_{t\bar t}$) at LHC. We show that in this ratio a
major fraction of virtual contributions (including QCD components) disappears,
leaving a residual dominant electroweak Yukawa effect that might be strongly
enhanced in the presence of supersymmetry. A quantitative numerical analysis of
the size of the effect is also performed under the assumption of a relatively
light supersymmetric scenario.
