TORONTO (Reuters) - Toronto's main stock index finished lower for a fourth straight session yesterday as investors continued to pocket gains after the index staged a remarkable rally from the five-year low it hit in March.

The TSX index fell to its lowest closing level since May 22, with the sell-off driven primarily by commodity shares, which were hit by a drop in oil prices and news of a production cut at key fertiliser maker Potash Corp. of Saskatchewan .

Shares of Potash Corp. were the biggest drag on the index, falling 10.8 percent to C$107.91 after the company announced additional potash production cuts late on Tuesday.

Energy companies were among the loss leaders as the price of oil fell further from the 2009 high above $73 a barrel reached last week.

That knocked Suncor Energy shares down 4.86 percent to C$34.42, while shares of EnCana Corp. dropped 3.4 percent to C$57. The energy sector fell 3.45 percent.

Since the TSX touched a near eight-month high of 10,726.01 last week, which put it 43 percent above the March low, many investors have opted to take profits.

Market analysts said the pull-back was overdue.

"I've been increasingly cautious as markets had continued to surge because a lot of this surge is built on the assumption that the economy will recover very strongly in the second half of this year and into next year," said Elvis Picardo, analyst and strategist at Global Securities in Vancouver.

"That may or may not be the case and it makes sense for us to pause here, consolidate and evaluate the near-term and the medium-term outlooks."

The S&P/TSX composite index ended down 241.29 points, or 2.34 percent, at 10.066.11. Nine of the TSX's 10 sectors ended lower. The consumer staples group advanced 0.13 percent.