Bob Dylan, Wilco and My Morning Jacket bring Americana to Merriweather

What is Americana, anyway? The genre tag is applied to rock bands that merge American roots music -- country, blues, R&B -- with modern, radio-friendly flourishes. The stylistic waters can get muddy, though. Songs can evoke the music of Woody Guthrie and also U2's "The Joshua Tree." Bands might augment wood-grain riffing with flourishes on loan from German experimental music of the late '70s. Americana is not necessarily traditional, and the nostalgia does not stop at regional or national border...