The Inheritance of Flower Color
Today, cultivars of petunia are found in an astounding range of colors including
whites, yellows, pinks, mauves, reds, magentas, lavenders, and purples with one notable
exception of blue. Additionally, all of these colors are found in different combinations
together in bicolors, tricolors, picottees, flecked phenotypes, dark throats with light face,
light throats with dark face, etc.. Thus, one could correctly assume that the genetics
controlling flower color in petunia is quite complicated.
Flower color in petunia is primarily due to the presence or absence of the six
different anthocyanidins: cyanidin, peonidin, delphinidin, petunidin, malvidin, and
pelargonidin (Wiering and de Vlaming, 1984). In petunia these different anthocyanidins
occur individually or together in many different combinations. Furthermore, the way in
which each anthocyanidin is hydroxylated, glycosilated, methylated, and acylated to form
anthocyanins is also very critical in determining the actual flower color. In addition to
the type of anthocyanin, there are many compounding factors including the presence or
absence of copigments in the vacuole, the vacuolar pH, and the shape of the cell that also
play an important role in determining flower color. The patterning and venation of a
petunia corolla is also quite complicated and is controlled by a totally different set of
genes. As you can see, the genetics of flower color is entirely too difficult to summarize
without breaking these different factors into 10 different groups of genes based on what
factors they control. These ten groups control anthocyanin expression, hydroxylation,
glycosilation, methylation, acylation, the type and content of copigments like flavonols,
venation pattern, flower color intensity, pH, and pollen color (Wiering and de Vlaming,
1984). Within these 10 groups there a least 40 different genes that all have different
patterns of inheritance. Some genes only have two alleles that are either dominant or
recessive, some are multiallelic and codominant, some loci are epistatic to others, and
some loci have lethal alleles (Wiering and de Vlaming, 1984). Because there are so
many different genes associated with flower color, linkage between these genes is a
problem that prevents the development of blue flowered petunias. For example, although
there are anthocyanins present in some cultivars that are typically blue they are present at
vacuolar pH’s that make them appear red.