Dec 22 (Reuters) - Canada’s main stock index treaded water on Tuesday as gains in the energy stocks were capped by weakness in materials sectors, while concerns around a fast-spreading mutant variant of coronavirus in the United Kingdom kept sentiment in check. * At 9:44 a.m. ET (14:44 GMT), the Toronto Stock Exchange’s S&P/TSX composite index was up 1.12 points, or 0.01%, at 17,502.01. * The energy sector climbed 0.3%, while the materials sector, which includes precious and base metals miners and fertilizer companies, lost 0.4%. * The financials sector slipped 0.2%. The industrials sector rose 0.1%. * On the TSX, 73 issues were higher, while 135 issues declined for a 1.85-to-1 ratio to the downside, with 12.48 million shares traded. * The largest percentage gainers on the TSX were fuel-cell products developer Ballard Power Systems Inc, which jumped 7%. * Its gains were followed by software firm Lightspeed POS Inc, which rose 2.8% after brokerage Credit Suisse started coverage of the stock with an “outperform” rating. * Apparel maker Canada Goose Holdings Inc fell 3.9%, the most on the TSX, and the second biggest decliner was Air Canada, down 1.5%. * The most heavily traded shares by volume were Bombardier Inc, Avalon Advanced Materials Inc, and Canadian Imperial Bank of Commerce. * The TSX posted five new 52-week highs and no new lows. * Across all Canadian issues there were 42 new 52-week highs and one new low, with total volume of 33.52 million shares. (Reporting by Amal S in Bengaluru; Editing by Shailesh Kuber)