Thomas Quasthoff, the German bass-baritone scheduled to sing Mahler's


in Philadelphia Orchestra concerts led by Christoph Eschenbach starting tomorrow, has canceled his appearances.

Quasthoff, citing vocal fatigue, first cut only Friday's appearance. But he then developed a bronchial infection, said orchestra vice president Kathleen van Bergen, and will not travel to the United States for any of the concerts.

Instead of the Mahler, the orchestra - pending a vote by the musicians last night - has moved up performances of Vivaldi's Four Seasons already scheduled for concerts on Jan. 25 and 26. The program for tomorrow, Thursday and Saturday will be Vivaldi, with four soloists from the orchestra, and Bruckner's Symphony No. 9.

The program for the Carnegie Hall concert Jan 23, which was to be the Mahler and Bruckner, will change - most likely to Bruckner and a Mozart piano or violin concerto. The orchestra yesterday was still working to find a soloist.

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