Streptocarpus - Genes and Inheritance

Genes and Inheritance

Flower Color Genes in Streptocarpus The following is adapted from an overview provided by Dr Jeff Smith at Ball State University, US.

The following is a quick summary of 1950s publications by Lawrence and Sturgess,

Colour genes

V = places pigment in the flower stems

F = places pigment in the petal cells

V and F are both necessary to give color, but do not control which color. When V or F are recessive (vv or ff) the flowers will lack any color and will be white in appearance.

I = color intensity. II = intense color, Ii = medium color and ii = pale color. This gene doesn't control "which color", just how "intense" the final color will be in appearance.

The actual flower color genes are named O, R, and D. Where the second copy of the gene is given as a "_", the second copy can be either dominant or a recessive. For example, in Blue flowers, only one dominant of each the three genes is needed (e.g. the O gene could be either OO or Oo, and it wouldn't matter which).

Blue = O_R_D_

Magenta = ooR_D_

Pink = oorrD_

Mauve = O_R_dd

Rose = ooR_dd

Salmon = oorrdd

Other genes affect the pattern of color or modify the final color. Some of these genes are:

B = gives a blotch of color in the throat of the bloom. The recessive "bb" produces flowers without a blotch. The trait appears to produce a darker or more intense version of the color of the outer edges of the petals. Thus, you can get dark pink blotches on a lighter pink flower etc.

H = gives color on the capitate hairs of the pistil. The recessive "hh" gives white or colorless hairs.

Genes F, I, B, and H are very closely linked and are usually inherited as a single unit. Therefore, many plants have pigmented flowers with at least medium intensity of color, and blotches in the throat, or have white flowers without blotches.

C = adds a co-pigment to the flower color. This gene modifies the appearance of the color, giving a bluish tint to the overall color. Plants with the recessive "cc" combination have flowers that are "brighter" in appearance. In the Mauve-Rose-Salmon series, the dominant gene produces undesirable murky colors.

L = puts nectar guides in the flower tubes. The recessive "ll" produces flowers without the lines.

Y = puts a yellow central stripe in the flower tube. I suspect that the size of the yellow area changes with "YY" versus "Yy" plants. The recessive "yy" would produce flowers with no yellow in the flower tube.

Other genes are mentioned in the original articles, but they appear to involve some rarely seen color modifications. Genes for plant size, fragrance etc. were not mentioned in these articles.