  We compute the spectrum of the low-lying mesonic states with vector, scalar
and pseudoscalar quantum numbers in QCD with one flavour. With three colours
the fundamental and the two-index anti-symmetric representations of the gauge
group coincide. The latter is an orientifold theory that maps into the bosonic
sector of $\mathcal{N} = 1$ super Yang-Mills theory in the large number of
colours limit. We employ Wilson fermions along with tree-level improvement in
the gluonic and fermionic parts of the action. In this setup the Dirac operator
can develop real negative eigenvalues. We therefore perform a detailed study in
order to identify configurations where the fermion determinant is negative and
eventually reweight them. We finally compare results with effective field
theory predictions valid in the large $N_C$ limit and find reasonably
consistent values despite $N_C$ being only three. Additionally,the spin-one
sector provides a novel window for supersymmetric dynamics.
