By Erik Kirschbaum
BERLIN (Reuters) - Chancellor Angela Merkel's chances of preserving her center-right coalition were in doubt less than a week before a federal election, with a new anti-euro party rising in the polls and her current partner reeling from a regional setback in Bavaria.
An emphatic victory in Bavaria on Sunday for the Christian Social Union (CSU), sister party to Merkel's Christian Democrats (CDU), was overshadowed by recent poll gains for the Alternative fuer Deutschland (AfD) and the collapse of the Free Democrats (FDP) in the rich southern state.
Should the AfD clear the five percent threshold needed to enter the national parliament in the federal vote on Sunday, or if the FDP fails to clear that mark, then Merkel has virtually no chance of securing another center-right majority.
While she will most likely remain chancellor, her conservatives would be forced to enter difficult coalition negotiations with the Social Democrats (SPD), in which they would have to cede key ministerial posts to their center-left rival and accept SPD demands on tax and wage policy.
"The big uncertainty now is the AfD," said Thomas Jaeger, a political scientist at Cologne University. "They weren't on the ballot in Bavaria but could get 5 percent nationally on Sunday."
The German election is being closely watched by Berlin's partners in Europe, with some hoping that a "grand coalition" between Merkel and the SPD would lead to pro-growth policies and a more conciliatory approach towards struggling southern euro nations.
The latest poll from Emnid over the weekend showed support for Merkel's conservative bloc of CDU and CSU at 39 percent and the business-friendly FDP, her current partner in Berlin, on 5 percent, short of a combined majority.
In Bavaria, the FDP crashed out of the state assembly with a score of just 3.3 percent. That took some of the shine off a romping win for the CSU, whose leader Horst Seehofer won an absolute majority in the regional parliament with 47.7 percent of the vote.
The Emnid poll showed the AfD, which calls for an "orderly dismantling" of the euro zone, up one point to 4 percent. After languishing in the 2-3 percent range for months, pollsters and analysts now believe the AfD has a good shot at pushing above 5 percent on Sunday.
A strong score for the AfD would make it more difficult for Merkel to return to power in a centre-right coalition. On Monday, the AfD was staging an event at the Brandenburg Gate to mock Merkel and European Central Bank President Mario Draghi's handling of the euro crisis.
Hermann Groehe, general secretary for the CDU and the party's campaign manager, said the CSU's success in Bavaria would provide a "tailwind for the conservatives across Germany."
But a rift between Merkel and Seehofer over the CSU leader's push for a new motorway toll for foreigners cast a shadow over the celebrations.
"We're against a motorway toll," Groehe said. "We've got different views on that. But we're not going to hold coalition negotiations in public about that a week before the election."
Groehe and other conservative leaders urged voters to cast both their ballots for the CDU/CSU and not split their two votes by giving the FDP their so-called "second ballot". The FDP, however, launched urgent appeals for those second ballots.
Germans pick a constituency candidate with their first vote, and the second vote determines the relative strength of the parties in the Bundestag. In the past, the CDU/CSU tacitly encouraged its voters to back the FDP with the second vote.
(Reporting By Erik Kirschbaum; Editing by Noah Barkin)