By Stephen Brown BERLIN, May 10 (Reuters) - Voters in Germany's most populous state North Rhine-Westphalia (NRW) punished Chancellor Angela Merkel's centre-right coalition in a local election on Sunday, robbing her of her majority in parliament's upper house. After her first electoral test since she formed a coalition government with her pro-business allies six months ago, Merkel must now build a new partnership in NRW or see the opposition take control of the state she has controlled since 2005. Below is a look at various scenarios: MERKEL'S CONSERVATIVES AND SDP IN "GRAND COALITION" * Probability: possible Merkel's conservative Christian Democrats (CDU) said on Monday they would be ready to form a "Grand Coalition" with the opposition Social Democrats (SPD), echoing the uneasy formation of her national government until she switched last year to an alliance with the Free Democrats (FDP). Both the CDU and FDP fared badly in Sunday's vote, with the CDU falling 10 points to 34.6 percent. The centre-left SDP came in marginally behind the CDU in percentage terms but equal in terms of seats in the regional assembly. A partnership would offer the two biggest parties a solid working majority, made easier by the fact that their candidates for state premier, CDU incumbent Juergen Ruettgers and the SPD's Hannelore Kraft, refrained from attacking each in the campaign. But both the CDU and SDP already insist that they should have the state premiership, promising tough negotiations ahead. SDP, GREENS AND LEFT * Probability: possible The SDP, boosted by the NRW vote after their worst result since World War Two in last year's federal vote, would prefer an alliance with the Greens -- the biggest winners in the NRW vote, nearly doubling their votes to 12.1 percent -- but would need the growing hardline Left party to build a stronger majority. Taking over NRW would make the SDP and Greens, who governed Germany together from 1998 to 2005, a more formidable opposition to Merkel at the national level. But a partnership with the Left would be fraught for the SDP, many of whose members loathe the small party for deserting the SDP and joining up with former East German communists. Another possibility would be for the SDP and Greens to make a coalition and count on the Left, which just managed to exceed the 5 percent threshold, as an external ally offering support for the other two when necessary. CDU AND GREENS *Probability: unlikely A coalition between the CDU and Greens would be indigestible for the more conservative and business-oriented factions of Merkel's party, especially some areas of energy policy where the CDU is committed to extending the lives of some nuclear plants. But a so-called "Black-Green" alliance could serve as a model for a new-look future federal government and the formula has already been tested on a smaller scale in the city state of Hamburg. Merkel, with her interest in the environment, is believed to be interested in this option but it would risk creating tensions with between her conservatives and the FDP, which has expressed concern that she has been flirting with the Greens. OTHER ALTERNATIVES Theoretically the CDU or SPD could seek an alliance with the Greens and the FDP but this is deemed highly unlikely. For a related election story, click on (Writing by Stephen Brown; Editing by Angus MacSWan) Keywords: GERMANY ELECTION/COALITIONS (firstname.lastname@example.org; +49-30-2888-5216; email@example.com) COPYRIGHT Copyright Thomson Reuters 2010. All rights reserved.
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