(By Paul Virgo) (see related stories) Rome, April 18 - The Italian centre left's divisions were embarrassingly exposed on Thursday when the Democratic Party's (PD) candidate did not prevail in the first ballot to elect the new president after an internal rebellion. Senate Speaker Franco Marini failed to win the two-thirds majority needed in the first round, even though ex-premier Silvio Berlusconi's centre-right People of Freedom (PdL) party and other parties were also backing him. PD leader Pier Luigi Bersani selected Marini, a member of the Catholic wing of his party, in the hope that he could win broad cross-party support after talks with Berlusconi. Instead, Marini obtained 521 votes in the first ballot, well short of the magic number of 672, with many PD lawmakers coming out against an 80-year-old seen by some as a representative of Italy's tired old political class. The outcome is set to increase the pressure on Bersani, who was already under fire over his handling of Italy's political deadlock since February's general election. His centre-left alliance came first in the election but failed to win a working majority in the Senate after he conducted a colourless campaign. Italy still has no government as Bersani failed in a bid to reach out to the anti-establishment 5-Star Movement (M5S), which holds the balance of power in the Senate. He has refused to consider forming a broad coalition government with the PdL, while at the same time rejecting calls for another vote, saying that this would be equally inconclusive under the current election law. His most vocal critic has been Florence Mayor Matteo Renzi, the rising star of the PD who came second to him in the primary to select the centre left's premier candidate. Renzi announced Wednesday that the 50-odd parliamentarians loyal to him would not vote for Marini, saying electing him would be like playing a "prank" on the nation. He pointed out that Marini failed to win re-election to parliament in February. But the rebellion against Marini went beyond Renzi's supporters in the party. "I didn't vote for Marini. I was undecided about whether to cast a blank paper or vote for (M5S candidate Stefano) Rodota'," said PD Senator Laura Puppato, who also ran in the primary. "In the end I voted for Rodota'," she added, saying she was confused about why Bersani had failed to move after M5S leader Beppe Grillo hinted he would soften his line on a government pact if the PD voted for his movement's presidential candidate. "Bersani had done extraordinary things until yesterday. Then he turned towards the open sea just as he was about to enter the port". Former centre-left leader Walter Veltroni said Bersani should now drop Marini and try to find another candidate. "The result of the vote for the president is so clear that it would be a big mistake to insist in going down this road," Veltroni told ANSA. "The Democratic Party should offer a name or a limited list of names of people who don't belong to a political party and are esteemed and competent, like (1999-2006 President Carlo Azeglio) Ciampi". Thursday's second ballot is likely to be inconclusive as the PD has told its electors to cast blank papers and the PdL was expected to do the same. It is not clear whether the PD has done so to have a pause for thought or whether it is simply a tactic to effectively put things on hold in the second and third votes with the intention of proposing Marini again in the fourth ballot, when a simple majority of 504 will suffice. "I suffered great unease in the first ballot as I was torn between a responsibility to the party leader and awareness of how people outside the world of politics felt," said Simonetta Rubinato, a PD MP from Veneto. "In the end I decided to cast a blank paper in order to not be an accomplice in a decision that was rightly seen as being submissive to the will of Berlusconi".