Discussing interest rates at the 27th annual correspondent banking conference of Mercantile Trust Co. are Neal J. Farrell, president and chief operating officer of Mercantile; Norman M. Coats, director of the economic research department of Ralston Purina Co.; Robert O. Blomquist, executive vice president of Mercantile, and Eugenene A. Leonard, senior vice president of Mercantile and head of its correspondent banking division.