Venezuela's main opposition parties have agreed to back a single candidate to challenge President Hugo Chavez in December elections.

The opposition Wednesday selected Manuel Rosales as its top choice to face the Venezuelan leader.  Other opposition leaders who had declared their candidacies agreed to step aside so anti-Chavez forces could stand a better chance.

The move to back Rosales, governor of the western Zulia state, prompted the cancellation of a primary vote that was scheduled for this Sunday to select a single opposition candidate.

Earlier this year, President Chavez threatened to call a national referendum on remaining in office until 2031 if opposition parties boycotted the December elections.

Rosales told a cheering crowd he will be the president of all Venezuelans regardless of their differences.  He has accused the president of spending the nation's oil wealth abroad to promote his leftist agenda, while many Venezuelans face hunger and poverty at home.  Mr. Chavez has said he is working to improve the lives of the nation's poor.