BERLIN (Reuters) - Germany's Social Democrats (SPD), who share power with Chancellor Angela Merkel's conservatives, fell to their lowest level in 24 years in a poll published on Wednesday, underscoring the need for possible new alliances after the next election.
The two mainstream parties have suffered in the last six months from a shift toward the anti-immigrant Alternative for Germany (AfD) due to the migrant crisis. However, the personal popularity of Merkel, chancellor of Europe's biggest economy for the last decade, is cushioning her conservative bloc.
The Forsa poll put the SPD down 2 points on 19 percent, the first time in more than two decades that the party has fallen under the 20 percent mark with the pollster.
The SPD has polled below 20 percent in other surveys.
SPD leader Sigmar Gabriel is under pressure from some in his party to shift left before the next federal election in Sept. 2017 to try to mobilize traditional supporters.
Amid speculation he may quit as leader and whether he will stand against Merkel in 2017, he has invited others to put themselves forward so that party members can choose their candidate. So far none else has taken up the challenge.
The Forsa poll put Merkel's conservative bloc on 34 percent, unchanged from last week, and the opposition Greens up one point at 14 percent. The AfD is up 1 point at 11 percent.
Some analysts have suggested the main parties will be considering new partners to counter the rise of the AfD, including possibly a coalition between the conservatives and the Greens.
(Reporting by Madeline Chambers; Editing by Andrew Heavens)