The b--->s{\gamma} constraint in effective supergravities from string theory

We study the constraints from the $b{\rightarrow}s{\gamma}$ decay in the parameter space of effective supergravities from orbifold string theory and with minimal supesymmetric particle content. Both the general dilaton-dominated universal scenario as well as a non-universal scenario for the soft terms are investigated. It is found that the recently reported CLEO upper and lower bounds constrain the parameter space of the models under scrutiny. In particular we find constraints on the values of the parameter $\tan{\beta}$ and the gluino masses. In this class of string scenarios the negative sign of the Higgs mixing parameter $\mu$, is phenomenologically preferred.