Robert Plant and Alison Krauss made a surprise appearance Wednesday night (Sept. 17) during Levon Helm's concert kicking off the ninth annual Americana Music Festival and Conference in Nashville. They joined an already-impressive lineup of guests -- including Sheryl Crow, John Hiatt, Delbert McClinton, Billy Bob Thornton, Buddy Miller, Sam Bush and blues musician Little Sammy Davis -- for the show at the Ryman Auditorium. Plant and Krauss, whose duet album, Raising Sand, was released last year, performed "In the Pines," a song they first performed together in 2004 during a tribute to the late blues legend Huddie "Lead Belly" Ledbetter. Helm, best known for his work in The Band, is nominated in three categories of the seventh annual Americana Honors and Awards taking place Thursday night (Sept. 18) at the Ryman. At Wednesday's concert, he and his current band performed material from his Grammy-winning album, Dirt Farmer, and several classics from The Band, including "Rag Mama Rag," "The Shape I'm In" and "Chest Fever." To close the show, Helm and Hiatt traded verses on "The Weight" with vocal backing from the entire cast of the evening, along with singer-songwriters Steve Earle and Allison Moorer. They returned to encore with Bob Dylan's "Forever Young." The festival and conference continues through Saturday (Sept. 20).