Don't forget blues was part of bluegrass. That's one reason why blues/black gospel and bluegrass gospel so often turn up in each others' back yards. Also if you listen to blues fiddle, all you need to do is speed it up and it's bluegrass fiddle. I bet picking patterns do that too. And "high lonesome" singing sounds an awful lot like soloists singing spirituals-- pushing the pitch a tad sharp on long notes for emphasis. "High lonesome" is pitch shading as much as tone shading.

~S~