The move came after Wade's son, Karim Wade, was disqualified from contesting the race for the PDS because he was a dual citizen at the time he submitted his candidacy. He had been in the process of renouncing his French citizenship.

A week ago, the country's Supreme Court rejected a PDS attempt to have the election delayed. The party had argued that irregularities and alleged corruption led to the elimination of their candidate.

"Given the current situation, the PDS has an imperative duty to take a stand," the party said in a statement on Friday. "In this spirit of responsibility towards our homeland... our political group has chosen to give its full support to the Diomaye Faye Coalition."

Faye, 43, an anti-establishment candidate, is seen by analysts as one of the most serious challengers to the party of outgoing President Macky Sall, in a field of 19 candidates. Sall himself is stepping down after two terms.

Faye, a former tax inspector, is running in place of firebrand opposition leader Ousmane Sonko who was disqualified over a defamation conviction.

They were both released from jail last week under a new amnesty law after months in detention, and have since drawn thousands to their rallies.

Sonko has called on his supporters to back Faye, a concern for competitors as Sonko enjoys widespread support, particularly among young people frustrated with economic hardships and a lack of jobs in the West African country of 17 million.

President Sall served in Abdoulaye Wade's government before running against him in the 2012 election.

In 2019, Karim Wade's hopes of contesting the presidential race were scuppered by a conviction on corruption charges several years earlier. He has since been pardoned and had his right to run for office restored.

(Reporting by Ngouda Dione; Writing by Anait Miridzhanian and Portia Crowe; Editing by Frances Kerry)