While I have only my memory to back this up, when Rock and Roll was first starting out, they were refering to "Roots Music" as a code word for Black music, when they were discussing just such an influence on Elvis Presly. I think if you researched the term in conjunction with Elvis and the beginnings of Rock and Roll, you might have your answer (understanding that Elvis predated the Folk Revival by about ten years). I will be interested if my memories are correct.