Sept 16 (Reuters) - Canada’s main stock index opened lower on Thursday, weighed by weakness in commodity-linked stocks and as concerns about a stunted global economic recovery dented demand for world equities. * At 9:32 a.m. ET (13:32 GMT), the Toronto Stock Exchange’s S&P/TSX composite index was down 54.26 points, or 0.26%, at 20,639.53.