Repression of seed coat pigmentation in Ethiopian mustard

The inheritance of seed colour in Brassica carinata A. Braun was investigated in backcross and F-2 generations derived from two crosses between the brown seeded cultivar S-67 and two, true breeding, yellow seeded lines, PGRC/E 21164 and PGRC/E 21224 of the Plant Gene Resources Centre of Ethiopia. F-1 seed was identical in colour to self-pollinated seed borne on the respective brown and yellow seeded parents indicating maternal control of seed colour in B. carinata. F-1 plants of reciprocal crosses produced yellow seed that was somewhat darker than that of the yellow-seeded parent indicating incomplete dominance of yellow over brown. Backcross F-1 plants, derived from the backcross to the brown parent, segregated brown and light yellow-brown/yellow seeded plants in a 1:1 ratio, while backcrosses to both yellow seeded parents produced only light yellow-brown/yellow seeded plants. The F-2 generation segregated brown and light yellow-brown/yellow seeded plants in a 1:3 ratio. These results are in contrast to seed colour inheritance pattern observed in other Brassica species, where brown seed colour was fully or partially dominant over yellow. The apparent dominance of the absence of a gene product in yellow seed over its presence in brown seed, was explained by the presence of a dominant repressor gene (Rp) in yellow seed which inhibits the expression of seed coat pigment synthesis genes. The repressor gene is absent in brown seeded plants. The significance of this finding in relation to the development of yellow seeded lines in other Brassica species is discussed.