Green Party candidate Fritz Kuhn won Sunday's runoff election by a clear majority, taking almost 53 percent of the vote compared to just over 45 percent for Sebastian Turner, who does not belong to a political party but was backed by Merkel's Christian Democratic Union (CDU) and their junior coalition partners at the national level, the liberal Free Democrats.

The two men were the top finishers in the first round of voting two weeks ago. The election was forced into a runoff as none of the candidates had taken 50 percent of the vote in round one.

The election is just the latest blow to the CDU in the southern state of Baden-Württemberg after voters there elected a Green government in last year's election.

It was not clear to what extent the result might reflect general voter sympathies across the country less than a year before the next national election, but the southern state has seen a good deal of political controversy over the past couple of years.

Plans to build a new main train station in Stuttgart requiring more than 100 trees to be cut down led to a series of protests in September 2010 that saw dozens of people injured in clashes with police.

The project is set to go ahead following a referendum in the state last November in which nearly 60 percent of those who went to the polls voted in favor of it. Kuhn, who is a critic of the project known as Stuttgart 21, has said he will respect the result of that referendum.

Former CDU Premier Stefan Mappus also found himself at the center of controversy after he purchased a 45 percent stake in the local power company EnBW on behalf of the state - without consulting lawmakers. A court later ruled the 2010 deal unconstitutional. Prosecutors subsequently launched an investigation into Mappus on suspicion of breach of trust.

pfd/mkg (dpa, AFP)