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GENETICS OF FLOWER COLOR  by Wayne Handlos

1.   2.    3.    4.   

        5.     6.    7.    

8.     9.

1.‘Lass O’Gowrie’       Red A      R1R1 R2R2    5. ‘Preston Park’ Salmon E    R1r1 R2R2

2.‘Dolly Varden’           Red B       R1r1 R2R2     6.  ‘Verona’  Rose-pink G    R1R1 r2r2

3.‘A Happy Thought’    Red C       R1R1 R2r2     7.  ‘Mrs. J.C. Mappin’White I  r1r1 r2r2

4. ‘Miss Burdette Coutts’ Red D        R1r1 R2r2                

8.  Molecules of six pigments: cyanidin, pelargonidin, delphinidin, peonidin, petunidin, malvidin

9.  The six floral pigments (in fig. 8)  and their potential colors.

Most of the color of Pelargonium flowers is due to six pigments: cyanidin, pelargonidin,

delphinidin, peonidin, petunidin, malvidin. But the story gets more complicated as the

following information will show.

Much of our understanding of the genetics of color control in the flowers of zonal

Pelargoniums has been done by Tilney-Bassett and his students in Wales.

The most extensive and thorough research was done by H. Kabwazi including extensive

chromatographic studies to determine which pigments were present and their relative

concentrations.

It was determined that there were two complementary genes each with two alleles which

were designated as R1, r1, R2, r2. This conclusion was achieved by selfing and back-

crossing a number of different colored cultivars, then growing the seeds and counting the

different colored offspring that were produced by each cross. From this they came up

with the following genotypes:

R1R1 R2R2 – red flowered A

R1r1 R2R2 – red flowered B

R1R1 R2r2 – red flowered C

R1r1 R2r2 – red flowered D

r1r1 R2R2 – salmon flowered E

r1r1 R2r2 – salmon flowered F

R1R1 r2r2 – rose-pink flowered G

R1r1 r2r2 – rose-pink flowered H

r1r1 r2r2 – soft pink/white

Note that the cultivars in the group of red-flowered plants had a least one dominant

allele of each type of red gene (R1 and R2). The salmon-flowered cultivars were double

recessive (r1r1) for the R1 gene. The rose-pink cultivars were doubly recessive (r2r2)

for the R2 gene. The soft pink/white flowered plants carried all four recessive alleles (r1r1 r2r2).

These different genotypes are of interest because in a breeding program each cross

will give different kinds and ratios of offspring. For instance Red A will only produce red-

flowered offspring – no matter which of the others it is crossed with. But Red D when

crossed with any of the other genotypes will produce red, salmon, rose-pink and/or soft

pink-flowered offspring in varying ratios.

But zonal Pelargoniums do not come in only these four colors. Orange colored flowers

came into existence about 1990. Breeding tests established that orange was determined

by another gene – named Or or – and the orange color is due to the homozygous recessive

alleles – or or. When orange flowered plants were crossed with white flowered plants, the F1

generation had peach colored flowers and the F2 generation (from a self-pollinated peach-

flowered plant) produced orange (oror), peach (Oror) and white (OrOr) flowered offspring.

Purplish colored flowers are also known. It was proposed that there was another gene pair

called Pu pu which reacts differently with different combination of red, orange and crimson

genes. The salmon flowered plants will only produce salmon colored offspring no matter the

combination of crimson, orange and purple genes; similarly, the soft pink/white flowered

plants only produce soft pink/white offspring no matter what combination of crimson, orange

and purple genes are present. Purple (either magenta or purplish pink) is only produced by

crossing the appropriate reds with rose-pink flowered plants and then only if the dominant

 purple allele, Pu, is present.

The genetics of true white-flowered plants was also investigated and found to be due

to a gene for white flowers – Ww – interacting with the two genes for red. Thus a white-

flowered plant had to be homozygous recessive at all loci to be white flowered,

r1r1 r2r2 ww. All of the above genotypes have been reconfirmed in a doctoral thesis by

Wu (1999).

Munshi (1995, Ph.D. thesis) has analyzed the pigments present in flowers of different colors.

From the various crosses the following flower colors were obtained. These were then analyzed

 for the various pigments present and their relative quantities.

Light red – mv, pg, cy, pn* – Total pigment = 100% Relative proportions of pigments - 3, 1, 4, 2

Salmon – mv, pg, cy, pn – Pigment = 70-90% Relative proportions 2, 1a, 3, 1b

Soft pink – mv, pg, cy, pn – Pigment = 70% Relative proportions 2, 3, 4, 1

White – mv, pg, -, pn – Pigment = 6% Relative proportions NA (minimal pigment)

[*mv = malvidin = 1; pg = pelargonidin = 2; cy = cyanidin = 3; pn = peonidin = 4]

 One of the conclusions drawn from this research is that "the difference in the colors

of the flowers is not usually of a qualitative nature … but is of quantitative nature".

The variously colored flowers have the same pigments but they have them in different

quantities and in different proportions.

© 2017, Central Coast Geranium Society (CCGS )