July 29 (Reuters) - Canada’s main stock index rose at the open on Thursday, lifted by the materials and energy sectors as commodity prices firmed after the U.S. Federal Reserve doused prospects of an increase in lending rates. * At 9:34 a.m. ET (1334 GMT), the Toronto Stock Exchange’s S&P/TSX composite index was up 43.27 points, or 0.21%, at 20,273.67. (Reporting by Shreyashi Sanyal in Bengaluru; Editing by Aditya Soni) Our Standards: The Thomson Reuters Trust Principles.