Apart from the fact that dubbing was common practice in Italian cinema at the time, most actors were dubbed as the film makers wanted to retain the regional Florentine accent so important in the book.
In the book by Vasco Pratolini, 'La Signora' is clearly a lesbian figure entertaining very ambiguous relationship with her young female servants. This fact was omitted from the film because the Italian censorship would not allow homosexuals to be portrayed on screen at the time.
The film met with vehement opposition from the Italian government and was banned from export after it received the Special Jury Award at Cannes.