It was all smiles from the winner of Italy’s first ever primary vote to select a candidate for a general election.Romano Prodo was overwhelmingly backed by the electorate to lead the centre-left challenge to oust Prime Minister Silvio Berlusconi. That showdown is due by next May. Prodi won 75 percent of the vote. His nearest rival was a veteran communist leader who took just 15 percent. Around four million people turned out to vote, many more than had been expected. Berlusconi’s supporters claimed Sunday’s vote would be rendered meaningless by a change in the electoral system that the government looks set to introduce by the end of the year. The reform will usher in a complex version of proportional representation for the 2006 election. Opposition leaders say it was devised to try to help the conservative government stay in power.