Is it permissible for the Imam to speak on a topic other than straightening the rows after the Iqamah of the prayer?

Speaking after the Iqama is permissible if there is an overriding need for the Imam or the congregant. This is evidenced by the Prophet, peace and blessings be upon him, who privately conversed with a man after the Iqama for prayer. This is permissible, especially for important matters, but it is disliked.