HARRISBURG, Pa. - Gov. Tom Corbett's biggest campaign donor is upping its ante in Pennsylvania's race for governor that will exceed $50 million.

The Republican Governors' Association said Wednesday that it gave Corbett's campaign $3.5 million in recent weeks. It had already given him $1.8 million as the GOP incumbent tries to fend off Democratic challenger Tom Wolf.

The Washington-based GOP fundraising group is chaired by New Jersey Gov. Chris Christie, who says he backs Corbett, despite his lagging in the polls.

Campaign finance reports filed with the state are current through June 9. They show Corbett and Wolf spending a combined $26 million, while the three Democrats who lost to Wolf in the May primary reported spending another $22 million.

The next reports are due Sept. 23. The election is Nov. 4.