COMMODITIES-Oil up for fifth day, corn nears record highs

* Oil edges up on vague Bernanke remarks, Iran

* Corn approaches all-time high of nearly $8 a bushel

By Barani Krishnan

NEW YORK, July 17 (Reuters) - Oil rose for a fifth straight day on Tuesday, proving its resilience to other commodity markets, after Federal Reserve Chairman Ben Bernanke left the door open for more stimulus but did not say when that would occur.

Grains markets, like oil, retained their bullish streaks as the worst drought since 1956 in the U.S. Midwest pushed corn prices near the record highs of last summer.

Bernanke said the central bank was prepared to boost a slowing U.S. economy but gave few other hints, leaving financial markets to interpret his testimony to Congress. U.S. stocks and the dollar rose from earlier lows, while bonds fell .

The Thomson Reuters-Jefferies CRB index, a benchmark for commodities, settled slightly down, with 12 of its 19 components ending in negative territory. Cotton led the index's slide, falling more than 3 percent. Copper and gold fell too .

The biggest gainer of the day was U.S. crude oil, the CRB's main component, which rose nearly 1 percent.

U.S. crude's front-month contract ended up 79 cents at $89.22 per barrel. London's benchmark Brent crude finished up 0.6 percent, or 63 cents, at $104.

"It's post-Bernanke buying because, while he was not explicit about doing something, the door is clearly open," said John Kilduff, partner at Again Capital LLC in New York.

Oil prices have been on a tear over the past two weeks, after the selloff in commodities that began in early May subsided. U.S. crude is up 14 percent since hitting a near nine-month low of $77.28 on June 28.

The rally in oil -- supported partly by tensions between the United States and fourth largest oil exporter Iran -- has held up despite spotty economic data that has often weighed on other markets.

Iran's lingering dispute with the West over Tehran's nuclear program and recent North Sea supply interruptions also were supportive to oil in Tuesday's session.

Some traders said those factors could lose their impact if economic worries continued to mount, without the promise of remedies like an U.S. stimulus.

"The Iranian uncertainty and the North Sea problems are keeping oil supported, but I don't think those factors will last that long," said Mark Waggoner, president at Excel Futures Inc in Bend, Oregon.

Corn prices, already at 13-month highs and up 45 percent this summer, neared their all-time peak set last summer of nearly $8 a bushel as the expanding U.S. drought dimmed harvest prospects in the world's top exporter of the grain.

The Chicago-traded spot corn contract settled up 2-3/4 cents at $7.79-1/2 a bushel. It rose during the session to $7.96-1/2 -- a 13-month peak and just short of the record high of $7.99-3/4 set last summer. (Editing by Bob Burgdorfer)