Occasional black seeds are noticed in 'Bragg' seed lots obtained from large multiplication plots. The frequency of such seeds varies from 10^-5 to 10^-7, indicating that the black seeds result from spontaneous mutation. The plants grown from black seeds are identical to Bragg plants in every respect so that, without opening the pods on mature plants, it is impossible to distinguish the two types of plants .
Malik, S. S. and Singh, B. B.
"Research Notes: Isozymic variations in black- and yellow-seeded isogenic
lines of 'Bragg' soybean,"
Soybean Genetics Newsletter: Vol. 4
, Article 9.
Available at: https://lib.dr.iastate.edu/soybeangenetics/vol4/iss1/9