Although the piano concerto is an undeniable staple of orchestral repertory, contemporary composers have not done well by this esteemed genre. So it is not surprising that the enterprising pianist Awadagin Pratt commissioned—through the Art of the Piano Foundation—seven young composers to write works for piano and string orchestra. Under the baton of guest conductor Yaniv Dinur, the San Diego Symphony and Pratt performed Jessie Montgomery’s Rounds for Piano and String Orchestra Thursday at La Jolla’s Conrad Prebys Performing Arts Center. One of Pratt’s seven commissions, Montgomery’s brilliant, 15-minute concerto packs into a single movement the thrill and challenge of…