(Adds portfolio manager quotes and details on bond yields and updates prices)
* TSX closes down 269.65 points, or 1.73 percent, at 15,273.68
* Index close is lowest in nearly five months
* Largest drop for the index since September
* All of the TSX's 10 main groups fall
By Fergal Smith
TORONTO, May 17 (Reuters) - Canada's main stock index slumped on Wednesday to its lowest close in nearly five months as global markets worried that U.S. President Donald Trump's pro-business economic agenda could be slowed by political scandals.
The pullback in global markets came as reports of a memo by former FBI chief James Comey suggested that Trump tried to interfere with a federal investigation.
"If we continue to have more material political controversies, it can dovetail into consumer and business confidence," said Patrick Blais, senior portfolio manager at Manulife Asset Management.
The most influential movers on the Toronto Stock Exchange's S&P/TSX composite index were dominated by financial companies, which make up roughly a third of the index's weight. The group slid 1.9 percent to a five-month low.
"(U.S.) Treasuries are being bought up, yields are down and that impacts the overall financial system." Blais said.
Canada's 10-year yield plunged 11.8 basis points to 1.455 percent. It touched the lowest intraday in nearly one month at 1.441 percent. Lower bond yields increase the value of insurance companies' liabilities and reduce net interest margins of banks.
Royal Bank of Canada shed 1.7 percent to C$91.45, while Toronto Dominion Bank fell 1.4 percent to C$62.26. Insurer Manulife Financial Corp dropped 4.3 percent to C$22.71.
Alternative lender Home Capital Group Inc, which reported a further decline in deposit balances, saw its shares stumble 3.2 percent to C$8.69.
The TSX closed down 269.65 points, or 1.73 percent, at 15,273.68. It was the largest drop for the index since September.
All of the index's 10 main groups ended lower.
The materials sector, which includes precious and base metals miners and fertilizer companies, fell 0.6 percent even as gains for gold stocks helped temper declines.
Bullion reached a two-week high as the Trump scandals and weak U.S. economic data trimmed expectations the Federal Reserve would aggressively raise interest rates this year, pushing the U.S. dollar to its weakest in six months. A weak greenback makes the precious metal cheaper for non-U.S. investors.
Barrick Gold Corp rose 1.0 percent to C$23.26, while Agnico Eagle Mines Ltd was up 0.9 percent at C$67.39. Gold futures rose 2.0 percent to $1,259.2 an ounce.
Oil and gas stocks retreated 2.1 percent despite higher crude oil prices. Enbridge Inc fell 2.2 percent to C$52.65.
Industrials declined 2.4 percent as railroad stocks lost ground. (Additional reporting by Solarina Ho; Editing by Paul Simao and Steve Orlofsky)