Russian-born conductor Yakov Kreizberg will replace ailing Philadelphia Orchestra music director Wolfgang Sawallisch on the orchestra’s upcoming tour of North and South America. Kreizberg, a rising star in the conducting world, has conducted recently in Philadelphia, but will get only two rehearsals with the Philadelphians before the start of the tour. Sawallisch was forced to bow out of the tour this week when fatigue and other health problems caught up with him during a recent stretch of high-profile performances.