Joseph Fielding Smith attributes priesthood ban to Joseph Smith's teachings.
Joseph Fielding Smith, The Way to Perfection (Salt Lake City: Deseret Book, 1931), 111
Joseph Smith has left very little on record in his own words outside of the Pearl of Great Price. . . But we all know it is due to his teachings that the Negro today is barred from the Priesthood. The Negro may be baptized and enter the Church; and some of these unfortunate people have been baptized and have proved their faithfulness and worthiness before the Lord, in this their second estate, setting examples in righteousness which many of the sons of Shem and Japheth could emulate with everlasting profit. Surely the Lord will remember their faithfulness and reward them accordingly.