(Adds trader quotes and details throughout on activity; updates prices to close)
* TSX closes down 17.52 points, or 0.11 percent, at 16,144.79
* Index falls for first time in 12 sessions
* Seven of the TSX's 10 main groups end lower
By Fergal Smith
TORONTO, May 22 (Reuters) - Canada's main stock index edged lower on Tuesday, breaking its longest winning run in more than four years as shares of energy and materials companies lost ground.
The S&P/TSX composite index closed down 17.52 points, or 0.11 percent, at 16,144.79.
The decline left the index short of matching the 12 session winning sequence achieved in 2014 and on four other occasions since 1981, according to Thomson Reuters data.
The TSX, which was closed on Monday for the Victoria Day holiday, has lagged many other major stock markets in 2018. But its recent string of gains has helped lift the index to near positive territory for the year.
"It is an old fashioned rally led by financials and oil companies," said Bruce Latimer, senior equity trader at Eight Capital. "People are waking up and realizing that oil is $72 a barrel and these companies are making money."
The energy group ended 0.9 percent lower on Tuesday but is up about 28 percent since February, while the financials group, which accounts for more than one-third of the weight of the TSX, has climbed 6.5 percent since mid-April.
Gains for financials have come as bond yields have moved higher. Higher bond yields reduce the value of insurance companies' liabilities and increase net interest margins of banks.
Canadian banks begin to report second quarter earnings this week. Investors will be looking to see the impact on profits of new tighter rules on mortgage lending.
On Tuesday, the largest decliner on the TSX was uranium producer Cameco Corp, which fell 6.8 percent.
The materials group, which includes precious and base metals miners and fertilizer companies, declined 0.6 percent.
Seven of the index's 10 main groups ended lower.
Among the most active Canadian stocks by volume were Aurora Cannabis, up 5.8 percent to $8.38; Cenovus Energy , up 1.0 percent to $14.35 and Canopy Growth Co , up 9.4 percent to $39.44. (Reporting by Fergal Smith; Editing by Sandra Maler)