ANALYSIS OF GENIC MALE-STERILITY IN BRASSICA-OLERACEA

The male sterility system MS-1 of Brassica oleracea was studied in ord er to elucidate if nucleo-cytoplasmic interactions determine this syst em. Crosses of male sterile MS-1 genotypes with heterozygous MS-5 geno types gave fully fertile F1 progenies. Selfing of seven F1 plants resu lted in five F2 populations showing a 9:7 segregation ratio and two a 3:1 ratio for fertile and male sterile plants. Two F2 progenies deviat ed from the expected 9:7 or 3:1 segregation ratios for fertile and mal e sterile plants. Thermosensitivity and distortion of the meiosis are suggested as the causal factors underlying the deviation of the segreg ation ratios. It was concluded that nuclear factors determine the male sterility in the MS-1 system, because the presence of a nucleocytopla smic interaction in this system should have given only a 3:1 segregati on ratio for fertile and male sterile plants in the F2 generation.