* TSX rises 438.30 points, or 3.76 percent at 12,109.26
* Biggest one-day gain since May, 2009
* All 10 sectors advanced
By Trish Nixon
TORONTO, Aug 9 (Reuters) - Toronto's main stock market index had its biggest one-day rally in two years on Tuesday in a wildly volatile session, as the U.S. Federal Reserve said it will keep interest rates near zero for at least two more years in a bid to spur growth.
The rally ended a three-session rout that had knocked Canadian stocks down nearly 9 percent on worries about another U.S. recession following an embarrassing downgrade of U.S. debt.
"You've got two years of zero interest rates in the States. So there's no danger of any recovery being sort of sideswiped by the Fed raising rates," said Gavin Graham, president at Graham Investment Strategy.
"You are seeing the more economically sensitive sectors doing quite well ... you are seeing a rebound from some of the oversold things like the REITS and the financials."
Trading was volatile, with the index briefly turning negative following the Fed statement before surging in late trading.
Financial issues led the rally, up 3.94 percent, with banks making up half of the top 10 most influential gainers.
Bank of Nova Scotia (BNS.TO) topped the list, up 5.7 percent at C$52.78, followed by Toronto Dominion Bank (TD.TO), up 4.7 percent at C$75.02, and Royal Bank of Canada (RY.TO), which added 3.6 to trade at C$50.24.
The Toronto Stock Exchange's S&P/TSX composite index .GSPTSE closed the session up 438.30 points, or 3.76 percent at 12,109.26. All 10 sectors advanced, and each notched gains of 1 percent or more.
The rally made up for much of the previous session's sharp selloff, in which the index fell more than 4 percent to its lowest level in nearly a year.
Energy shares were up 3.9 percent, as crude oil futures turned positive in post-settlement trading. Canadian Natural Resources (CNQ.TO) was another top gainer, up 5.26 percent at C$34.79. (Editing by Jeffrey Hodgson)