The Boston Symphony Orchestra says that due to the positive test, Ma will not perform at the open rehearsal and concert with the Boston Symphony in the Shed planned for Saturday and Sunday, respectively. Soprano Renée Fleming will join the BSO on Sunday, delivering songs by Richard Strauss in place of the Shostakovich Cello Concerto No. 1 that was originally intended to be performed by Ma. The remainder of the program – including Stravinsky’s 1947 version of “Petrushka” – will continue as planned. Ma, 67, lives in the Berkshires and is one of the world’s most celebrated musicians, with accolades ranging from the Presidential Medal of Freedom to 19 Grammy awards.