GENETIC-CONTROL OF HIGH STEARIC-ACID CONTENT IN SEED OIL OF 2 SOYBEANMUTANTS

Stearic acid is one of the two saturated fatty acids found in soybean [Glycine max (L.) Merr.] oil, with its content in the seed oil of comm ercial cultivars averaging 4.0%. Two mutants, KK-2 and M25 with two-an d six-fold higher stearic acid contents in the seed oil than cv 'Bay', were identified after X-ray seed irradiation. Our objective was to de termine the genetic control of high stearic acid content in these muta nts. Reciprocal crosses were made between each mutant and 'Bay', and b etween the two mutants. No maternal effect for stearic acid content wa s observed from the analysis of F-1 seeds in any of the crosses. Low s tearic acid content in 'Bay' was partially dominant to high stearic ac id content in KK-2 and M25, and high stearic acid content in KK-2 was partially dominant to high stearic acid content in M25. Cytoplasmic ef fects were not observed, as demonstrated by the lack of reciprocal cro ss differences for stearic acid content in our analysis of F-2 seeds f rom F-1 plants. The stearic acid content in F-2 seeds of KK-2 x 'Bay' and M25 x 'Bay' crosses segregated into three phenotypic classes which satisfactorily fit a 1:2:1 ratio, indicating that high stearic acid c ontent in KK-2 and M25 was controlled by recessive alleles at a single locus. The data for stearic acid content in F-2 seeds of the KK-2 x M 25 cross satisfactorily fit a 3:9:1:3 phenotypic ratio. The F-2 segreg ation ratio and the segregation of F-3 seeds from individual F-2 plant s indicated that KK-2 and M25 have different alleles at different loci for stearic acid content. The alleles in KK-2 and M25 have been desig nated as st(1) and st(2), respectively. The stearic acid content (> 30 .0%) found in the st(1)st(1)st(2)st(2) genotype is the highest known t o date in soybean, but it was not possible to develop the line with th is genotype because the irregular seeds failed to grow into plants aft er germination. Therefore, tissue culture methods must be developed to perpetuate this genotype.