Gluino contribution to the three-loop beta function in the minimal supersymmetric standard model

We deduce the gluino contribution to the three-loop QCD beta function within the minimal supersymmetric standard model (MSSM) from its standard QCD expression. The result is a first step in the computation of the full MSSM three-loop beta function. In addition, in the case of a light gluino it provides the strong three-loop SUSY correction to the extrapolation of the strong coupling constant from the low energy regime to the Z region and up to the squark threshold.