Botswana holds an election on Wednesday that will present the first genuine challenge to the ruling Botswana Democratic Party (BDP) in its five decades of dominance over southern Africa’s wealthiest and most stable nation.

Whichever party wins will have to move swiftly to transform the economy, which since independence from Britain in 1966 has grown at 8% a year to become one of Africa’s most successful, but now risks coming unstuck because of over-reliance on a single commodity - diamonds.

Duma Boko, leader of the Umbrella for Democratic Change, is hoping to unseat the BDP of President Mokgweetsi Masisi on a promise to do just that. He is backed by former president Ian Khama, who handed over to Masisi last year but has since fallen into a bitter power struggle with him.

“We remain resolute and confident that we are going to win this election,” Boko told a news conference on Monday night before warning of possible fraud.

“I can only accept the result if the election is free and credible.” he added, raising the specter that Botswana, which has only known one-sided elections, could witness its first rancorous dispute over a tight result.

Of Botswana’s population of 2.2 million people, 924,000 registered voters will elect 57 national assembly and 490 local government representatives.

The winning party’s candidate then becomes president.

Polls open at 6:30 a.m. (0430 GMT) and close at 7 p.m.