Variegation in Plants-I

SUMMARY
The answer is that in nature variegation mimics herbivore damage. In a recent study in wild Caladiums, it was demonstrated that plants with more variegation attracted less butterflies which wanted to lay their eggs on the leaves, because the butterflies apparently thought that there were already caterpillars there which had eaten the white parts of the leaves. Obviously, a variegated plant can produce less energy because it has less chlorophyll. So it is an evolutionary trade-off between chance of herbivory and rate of autotrophy.

How modern commercial variegated plants are produced in species without natural variegation? They are produced in special radioactive chambers using tissue-culture explants. The radiation mutates/screws up the DNA of the plant, knocking out al lor some of the genes responsible for producing the chlorophyll which makes the leaf look green. This is almost somatic mutation, not generative (seed/polen-producing thissues) Plants like this can only be propagated vegetatively.

This is not  always in this case. Seeds can also be irradiated and then grown out using the same method, and there are other methods of forcing plants mutate, most famaously is by using a mutagen; a chemical agent which will change the DNA. But most variegated plants today are produced using nuclear radiation using the method as I describe above, because chemicals give less certain results and are more difficult to apply safely to the propagules.

There are only a few laboratories in the world with the facilities to mutate plants like this; Sydney in Australia, Gainsville in Florida, Wageningen the Netherlanfs, Ghent in Belgium, Tokyo in Japan. Breeders or investors in plant cultivars send their progagules to these labs to let them create varigated clones.

Before nuclear technology like this started (in the 1930’s already) variegated plants were obtained as random mutant seedlings or sports. Depending on the species, variegation can ocur naturally as a dysfunction of genetic machinery behind the metabolism of chlorophyll in around 1 of the 100.000 seedlings. Some plants like bushes or trees sometimes produce somatic mutant branches with variegation, which can be removed and propagated using grafting.  In a natural invorenment these clones usually die off the competition with normal plants, unless people cherish and propagate them. Mutant seedlings are often generative mutants, which carry their variegation to the successive generation, whereas mutant sports are usually somatic only and can only be propagated by cutting. Obviously, for a breeder generative mutants are the most interesting.