The true main theme comes from the clarinet and oboe in B minor.  
The recommended recording of it is Leondard Bernstein's 1987 one with the Royal Concertgebouw Orchestra, which comes paired with the composer's Fifth Symphony.  Woodwinds and brass are given equal presence to that of the strings, in this work that begins with an introductory passage in the cellos and basses.  The true main theme comes from the clarinet and oboe in B minor.  Not long after its composer finished his Ninth Symphony, he wrote its first two movements were written in 1822.  FTP, name this Eighth Symphony of Franz Schubert, left incomplete at his death.
The recommended recording of it is Leondard Bernstein's 1987 one with the Royal Concertgebouw Orchestra, which comes paired with the composer's Fifth Symphony.  
Unfinished Symphony (accept early buzz of Schubert's Eighth Symphon)