PARIS, Dec 8 (Reuters) - The French Socialist Party"s choice to run for president called on Wednesday for leftist parties to rally behind a single candidate in next April"s ballot, to be chosen via a primary election. Anne Hidalgo, who is also Paris mayor, said that, if the left did not unite, it "will find it impossible to continue to exist in our country". "We have no more time to lose," she added in an interview with broadcaster TF1, citing the need to give a higher political profile to topics such as climate protection and public education. According to opinion polls, none of the three left-leaning candidates for president would make it to a run-off with current President and frontrunner Emmanuel Macron, a centrist. Hidalgo is polling around 5% of votes, behind Greens candidate Yannick Jadot and Jean-Luc Melenchon of the far-left who are both in the high single-digit percent. None of the trio have previously commented on whether they would be willing to pull out of the race in support of a better-placed leftist candidate. Earlier on Wednesday, former economy and industry minister Arnaud Montebourg - a Socialist like Hidalgo who has been campaigning for the presidency on an independent ticket - said he would be ready to pull out and rally behind a joint left-wing candidate. France"s Socialists, the country"s most powerful party until 2017 when they controlled both chambers of parliament as well as the presidency were marginalised following the election of Macron, which altered the country"s political landscape.