Texas Comptroller Carole Keeton Strayhorn turned her back on the Republican Party and announced Monday she will run for governor as an independent.

The move allows Strayhorn to escape a potentially ugly primary battle against Gov. Rick Perry. The GOP primary is set for March 7.

Strayhorn, who calls herself "One Tough Grandma," has been a harsh critic of Perry's leadership over the past couple of years. Monday's announcement all but guarantees Perry will be the Republican candidate on the November ballot.

"I am a Republican," she said. "But I know we must set partisan politics aside and do what's best for Texas. That is why I am running for governor as a Texas independent."

Robert Black, a campaign spokesman for Perry, said the party switch is an admission that Strayhorn could not win the GOP primary, and he called the move "transparent political opportunism."

If elected, Strayhorn would be the first independent Texas governor since Sam Houston nearly 150 years ago.

To be listed as an independent on the November ballot, a candidate must gather 45,540 signatures in the spring from registered voters who did not vote in either the Democratic or Republican primary or any primary runoff in April.

On the Democratic side, the main candidates for governor are former Rep. Chris Bell and former Texas Supreme Court Justice Bob Gammage.

Strayhorn said of Perry: "He has given us higher property taxes, bigger government, higher insurance rates, toll roads, has abandoned our border and ignored our broken schools."

Both Strayhorn and Perry are former Democrats who switched to the GOP in the 1980s as the party rose to political dominance.

One of Strayhorn's sons, Scott McClellan, is President Bush's press secretary, and another son, Dr. Mark McClellan, is administrator of the federal Centers for Medicare and Medicaid Services.