AFRICAN powers Angola, Nigeria and South Africa on Friday endorsed the nomination of Nigerian Finance Minister Ngozi Okonjo-Iweala, a respected economist and diplomat, as a candidate to take over the World Bank.The United States faces an unprecedented challenge to its grip on the World Bank presidency, with emerging economies poised to nominate at least one candidate on Friday to set up the first contested bid for the top job at the global development lender."The endorsement is in line with the belief that the appointment of the leadership of the World Bank and its sister institution, the International Monetary Fund, should be merit-based, open and transparent,” the three said in a statement.South Africa chairs one of the three African seats on the 25-member World Bank board, and earlier this week sources said Okonjo-Iweala’s candidacy was being proposed after consultations between South Africa’s President Jacob Zuma and Nigeria’s President Goodluck Jonathan.