Soybean Hila Color

In soybean the pod is the ovary wall (pericarp) and the testa or outer coat and hila are the ovule wall. The ovule wall is maternal tissue or sporophyte tissue. The nuclear genome of the mother plant determines the genotype of all somatic cells produced through repeated mitotic divisions. The ovule wall is somatic tissue with the genotype of the maternal plant. The embryo may have a different genotype than the maternal parent when the maternal parent is heterozygous or when the embryo has been cross - pollinated.

Example:

F₁ plant is Ii genotype. I is a dominant inhibitor allele for yellow hila, i is a recessive allele for buff hila. Suppose an II (yellow) x ii (buff) cross is made to produce an Ii (yellow) F₁ plant. If the F₁ is self-fertilized, the F₂ generation will segregate 3 yellow:1 buff.

F₁ plant - all yellow hila seeds produced because the maternal tissue is Ii.

F₂ plants - 3/4 of the plants will produce yellow hila seed, 1/4 of the plants will produce seeds with buff hila color. A heterozygous (Ii) F₂ plant will produce all yellow hila seeds, because the testa and hila of these seeds is maternal tissue. However, one-fourth of the yellow hila seeds produced by an Ii maternal plant have ii (buff) nuclear genes. The ii nuclear genes do not produce buff hila seeds until the F₃ generation. Hila color is a maternal effect because the genotype of the maternal plant determines the color, regardless of the genotype of the individual seed.

F₂ generation maternal genotype is Ii.

1/4 II yellow hila, genotype: yellow
1/2 Ii yellow hila, genotype: yellow
1/4 ii yellow hila, genotype: buff

Ii F₂ plant - all seeds harvested from this heterozygous plant have yellow hila.

Seeds produced from self-fertilization of a heterozygous Ii F₂ plant.

The hila color is determined by the maternal plant genotype because the hila is somatic cell tissue. The genotype within the embryo is not expressed until the plant produces it's own seed.