(Update prices, add sector details) Jan 26 (Reuters) - Canada’s main stock index fell on Tuesday, dragged by weakness in the materials sector, while concerns about potential roadblocks to U.S. stimulus weighed on investor sentiment. * The materials sector, which includes precious and base metals miners and fertilizer companies, lost 0.5%. * Investors are watching the progress in the U.S. stimulus talks as lawmakers locked horns over the size of a pandemic relief package outlined by the new U.S. president Joe Biden. * At 9:45 a.m. ET (14:45 GMT), the Toronto Stock Exchange’s S&P/TSX composite index was down 20.27 points, or 0.11%, at 17,885.75. * Aurinia Pharmaceuticals Inc fell 4.5%, the most on the TSX, after brokerage Mackie Research downgraded the rating of the biotech firm and the second biggest decliner was Yamana Gold Inc, down 4.1% after the miner released its preliminary fourth quarter and 2020 production results. * The energy sector climbed 0.5% as U.S. crude prices were up 0.4% a barrel, while Brent crude added 0.6%. * The financials sector slipped 0.1%, while the industrials sector rose 0.4%. * On the TSX, 106 issues were higher, while 108 issues declined for a 1.02-to-1 ratio to the downside, with 21.54 million shares traded. * The largest percentage gainers on the TSX were TFI International Inc, which jumped 12.9% after multiple brokerages raised the price target of the logistics services provider’s stock. * Its gains were followed by Canopy Growth Corp, which rose 7.5% after pot producer launched a new line of Cannabidiol (CBD) products for pets. * The most heavily traded shares by volume were Blackberry Limited, Supreme Cannabis Company Inc, and Bombardier Inc. * The TSX posted 13 new 52-week highs and no new lows. * Across all Canadian issues there were 105 new 52-week highs and nine new lows, with total volume of 47.33 million shares. (Reporting by Amal S in Bengaluru; Editing by Shailesh Kuber)