The colour of a Clivia flower is controlled by the concentration or amount of two different pigments. One is yellow and this pigment is a member of the carotenoid or xanthophyll group (the name carotene comes from the carrot, in which there is a high concentration of carotene giving the orange colour).
The other is red and is a member of the anthocyanin group. This group varies in colour from pink to purple and is responsible for all the colours of flowers except yellow or orange. In the normal clivia flower the orange colour is caused by a mixture of yellow and red pigments. Variations in the orange colour are caused by changes in the concentrations of these two pigments. For example, reddish Clivia are caused by an increased concentration of the red anthrocyanin. If this higher concentration of anthocyanin is accompanied by a lower concentration of carotene then the red colour becomes a truer red (less orange tone). Thus to breed a true red one would have to breed out the yellow – in effect producing a white background instead of a yellow one.
In breeding light coloured orange flowers one has to decrease the concentration of red pigment. This leads to buff or flesh coloured flowers.
Now the concentration of red anthocyanin and yellow carotenoid varies in individual clivias in nature thus giving rise to the natural variation in orange colour observed in different clones of the plant. Selection of different coloured plants and breeding from them can intensify or decrease the colour.
Colour variation produced by mutation
The main mutation or “sport” to occur in Clivia miniata has been the yellow mutant. This has apparently occurred in nature a number of times as a number of different yellows have been collected. This mutation simply involves a failure of the biochemical reactions inside the plant which leads to the formation of the anthocyanin pigment. Without the red pigment, the only pigment present to colour the flower is the yellow carotenoid pigment, thus the flower is yellow. In Clivia plants (as distinct from the flowers) the anthocyanin pigment is also present. However it is only present in sufficient concentration to be seen at the base of the leaves. This is most noticeable in seedlings and young plants where it appears as a purple stain at the base of the leaves. It is purple because the mixing of red and green (chlorophyll) pigments produces purple. If the plant mutates so that it cannot produce anthocyanin then the flower will be yellow and the plant will be plain green without any purple stain.
Just as the orange flowers vary in concentration of the pigments giving rise to different tones of orange, in the total absence of anthocyanin there is still a variation in the concentration of yellow pigments giving rise to a variation in the depth of yellow colour. In other words some yellows are deeper coloured than others. Some are quite light in colour so that some parts of the flower can appear white. Thus a white clivia is simply a yellow mutant (no anthocyanin) in which there is so little yellow pigment that the flower appears white. As it require two chance occurrences in the one plant to produce a white Clivia from a normal orange one, white is much rarer in nature than yellow. However by deliberately crossing two pale yellow plants it should be possible to obtain whites or near whites in one or two generations.
The only other colour variants known at present in Clivia miniata are the so called pink forms. These I suggest come from the very pale orange (buff or flesh coloured) plants. These plants at times have a suggestion of pink in the flower. I believe these are the plants which, as well as a low concentration of anthocyanin, also have a low concentration of carotene. Thus a pink flower is one with low anthocyanin (red diluted to pink) superimposed on a white background instead of a yellow background.
Hence a breeding program for whites could also be used as a breeding program for pinks. This would be accomplished by crossing very pale yellow (or near whites) with pale orange flowers which have pinkish casts. Once really pinkish flowers were obtained then pink crossed with pink could be used to intensify the pink while secondarily further reducing the yellow pigment.
By Bill Morris
Clivia News No 1 1993