Quotron and AT&T; ended a joint venture.

American Telephone & Telegraph and Quotron Systems had planned to develop and market information services products, but the venture’s sales prospects among Wall Street firms were hurt by Citicorp’s recent $680-million acquisition of Los Angeles-based Quotron, an AT&T; spokesman said. Wall Street firms have said they would be reluctant to use an information service provided by a competitor such as Citicorp.