REPRESSION OF SEED COAT PIGMENTATION IN ETHIOPIAN MUSTARD

The inheritance of seed colour in Brassica carinata A. Braun was inves tigated in backcross and F-2 generations derived from two crosses betw een the brown seeded cultivar S-67 and two, true breeding, yellow seed ed lines, PGRC/E 21164 and PGRC/E 21224 of the Plant Gene Resources Ce ntre of Ethiopia. F-1 seed was identical in colour to self-pollinated seed borne on the respective brown and yellow seeded parents indicatin g maternal control of seed colour in B. carinata. F-1 plants of recipr ocal crosses produced yellow seed that was somewhat darker than that o f the yellow-seeded parent indicating incomplete dominance of yellow o ver brown. Backcross F-1 plants, derived from the backcross to the bro wn parent, segregated brown and light yellow-brown/yellow seeded plant s in a 1:1 ratio, while backcrosses to both yellow seeded parents prod uced 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 patter n observed in other Brassica species, where brown seed colour was full y or partially dominant over yellow. The apparent dominance of the abs ence 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 ye llow seed which inhibits the expression of seed coat pigment synthesis genes. The repressor gene is absent in brown seeded plants. The signi ficance of this finding in relation to the development of yellow seede d lines in other Brassica species is discussed.