UPDATE 1-Marchionne, Voser to step down from UBS board

* Marchionne, Voser will not stand for reelection in 2010

* UBS to inform on successors later

(Adds detail)

ZURICH, Sept 29 (Reuters) - Fiat (FIA.MI) chief executive Sergio Marchionne and Royal Dutch Shell (RDSa.L) chief executive Peter Voser will not stand for reelection to the board of UBS AG (UBSN.VX) next year, the Swiss bank said on Tuesday.

Marchionne was elected to the UBS board in 2007 and appointed vice chairman in 2008, while Voser was elected to the board in 2005. Neither will stand for reelection at UBS's annual meeting on April 14.

"Sergio Marchionne and Peter Voser would both like in future to focus on their current demanding management positions and have therefore decided not to seek any further mandates at UBS," the bank said in a statement.

Marchionne had been mentioned as a possible alternative CEO for UBS in the midst of its troubles earlier this year but the bank turned to former Credit Suisse boss Oswald Gruebel.

Marchionne, who suggested earlier this year he might step down from the UBS board, has been busy this year after Fiat absorbed 20 percent of bankrupt U.S. auto maker Chrysler.

Voser earlier this year announced a reorganisation of the oil company's worldwide exploration and production operations.

UBS, which was brought to its knees by the subprime crisis and had to be bailed out by the state while also suffering a damaging U.S. tax probe, said it would provide information at a later stage on candidates to succeed the outgoing board members. (Reporting by Emma Thomasson; Editing by Dan Lalor)