JOHANNESBURG (Reuters) - South Africa s ruling African National Congress holds an election this weekend to replace Jacob Zuma as party leader in a closely fought contest whose winner is likely to emerge as the nation s next president.  The front runners are Deputy President Cyril Ramaphosa, a former trade union leader and one of South Africa s richest people, and Zuma s preferred candidate, his ex-wife Nkosazana Dlamini-Zuma, a former minister and chairwoman of the African Union Commission. In a race seen as too close to call, seven candidates are seeking to succeed Zuma, who has been at the helm of the party for a decade. The stakes are high because the ANC s electoral dominance means whoever wins the party s top job is likely become the next president of South Africa after a national election in 2019. The party holds its conference in Johannesburg between Dec. 16-20. All seven ANC leadership hopefuls pledged to Zuma at a meeting last month that they would accept the outcome of the leadership vote in the interests of keeping the 105-year-old organization intact and avoid splits that could weaken its strength at the national elections in 2019. Ramaphosa edged Dlamini-Zuma by getting the majority of nominations to become leader of the party, but the complexity of the leadership race means it is far from certain he will become the next party leader and therefore the likely next president. Adding another level of complexity, delegates are not bound to vote for the candidate their ANC branch nominated. Zuma said last week he was  very happy  to be stepping down as ANC president. He can remain as head of state until 2019. Political uncertainty over the ANC race is a major threat to the country s credit rating. S&P Global Ratings and Fitch rate South Africa s debt as  junk .  Analysts have said South Africa s business and consumer confidence has been dented in recent years by allegations of corruption in Zuma s government and influence-peddling by the Gupta family - businessmen who are close friends of the president. Zuma and the Guptas have denied the allegations. Ramaphosa is viewed as more investor friendly and has pledged to fight the corruption that has plagued Zuma s tenure. Dlamini-Zuma has said she is not tainted by graft and it is fine if the country s white business community will not endorse her. She has said her priority is to improve the prospects for the black majority. 