April 30 (Reuters) - Canada's main index opened lower on

Tuesday, dragged down by materials stocks, while investors

assessed economic data at home and in the U.S. ahead of the

Federal Reserve's interest rate decision later in the week.

At 9:30 a.m. ET (1330 GMT), the Toronto Stock Exchange's

S&P/TSX composite index was down 91.41 points, or

0.42%, at 21,920.21.