(An edited and less illustrated article was originally published
by the Puget Sound Dahlia Association in "Dahlias of Today"
1996) Information from ......
Jean Knutson : 7335 34th Ave. Southwest : Seattle, WA 98126
There have been some rather famous experiments using barely sub-lethal doses of X-Rays to deliberately cause mutations in Dahlias, Including some in the Northwest. See Dahlias of Today 1981. The major work was reported in 1966 by C. Broertjes and J. M. Ballego in the Netherlands. Published in EUPHYTICA Vol.16 No.2 pp171-176. Wageningen, September 1967.
Another natural process that "scrambles" the genes is a process called Crossover that can occur as the chromosomes become tangled during their separation phase as a cell divides and grows. The process involves a bit of the end of one chromosome being detached and then reattached to the wrong chromosome, thus changing the genetic code. Usually the end bit of one is exchanged for the corresponding end bit of the other. This explains the small changes that are observed.
In any case, loss of, or change in the instructions to manufacture or produce one of the many required chemicals (proteins, sugars, enzymes etc...) will cause the color that was to result, to be changed in hue or saturation, or it may be lost entirely causing an underlying color to show through. The end result of severe losses is often white. Since rather a lot of damage must be done to deny all color, we often find that true white cultivars are lacking other healthy qualities which may have suffered collateral damage.
Some Dahlias obviously have a more fragile genetic makeup than others, and they do sport more often. Consider the pale yellow cactus KLANKSTAD KERKRADE first released in 1956. It sported in 1967 to give WHITE KERKRADE, an obvious loss of color. Ten years later KLANKSTAD gave MAJESTIC KERKRADE which has considerable warm pink blended towards the tips. This pink is just barely visible on the youngest petals of the parent. Not a new characteristic therefore, but changed in intensity. Since then there have been several sports of the apparently more fragile MAJESTIC, and some of them have sported also.
Lawrence & Scott-Montcrieff's monumental work on Color in the Dahlia in the '30's tells us that the Dahlia has multiple possible color controlling factors. All are subject to mutation. The code controlling them may be inherited on more than one chromosome. It could be up to four doses of the same information from each parent. This provides excellent redundancy, thus ensuring that most information is included at least once. This is also true for all of the instructions that a Dahlia needs to grow vigorously, but lets get back to color inheritance ...
The additional factors MAY cause an accumulating intensity of effect, like human skin color. There may be none or up to four.
Some words are: (factors are often called Genes, but Alleles would be more correct.)
no factor present = NULLPLEX
One factor = SIMPLEX
Two factors = DUPLEX
Three factors = TRIPLEX
Four factors = QUADRAPLEX
Ivory, symbol "I", begins to show in the Duplex condition and becomes a very pale yellow or cream at Quadraplex. The very pale lilacs and pinks are due to a factor called Pale Anthocyanin, symbol "A", which also shows increasingly with more factors. Ivory and "A" seem to interfere cumulatively with each other. Apparently both colors require the same precursor chemical and it is in limited supply and under its own genetic control. The competition causes a diminished effect of both "I" and "A". I suspect that MAJESTIC KERKRADE has more anthocyanin showing due to less competition because of a loss of an "I" factor from (probably Triplex or more) KLANKSTAD, leaving two "I"s. Further loss = PINK KERKRADE and loss down to Simplex = REGAL KERKRADE. LADY KERKRADE seem to have no signs of Yellow or Ivory at all. This is all supposition, of course, but it has an underlying logic that is somewhat compelling.icons leading to photos
Yellow, symbol "Y", is expressed fully in the Simplex condition and further factors have no visible effect. Much evidence indicates an inhibitor of yellow which may be inherited cumulatively to give certain delicate pale yellows and creams. These can be very similar to Quadraplex Ivory. There also seems to be an Intensifier of yellow, but observation of the suspected, extra bright, egg-yolk yellows like KENORA CANADA and KENORA SUNBURST will show a pale, almost suppressed, anthocyanin on the unopened petal reverse or perhaps a dark stem that indicates the presence of a touch of orange and the true reason for the extra saturation of color. Lawrence called these pseudo-yellow.
Intense Lavender and Purple and other highly saturated pigments are caused by Dark Anthocyanin, symbol "B", named by Lawrence from the famous dark foliaged, deep red flowered [B]ishop of Llandaff. This factor is also fully expressed in the Simplex condition. When Yellow is also present the dark pigment changes chemically to become one of the highly desired RED shades. Red may also result if "A" is multiplex enough to produce sufficient anthocyanin pigment. Some experimenting is in order here, but I feel that multi "A" reds will be the more sun proof ones that we are all looking for, or Probably multi "A" plus "B" on the required yellow base. The very sun resistant, dark foliaged Firemountain showed a loss of "B" mutation that supports this idea.
As a grower you have to be very lucky to have a whole plant sport or even a whole branch where it would be possible to get a cutting. Usually it is only a part of a bloom or even just a segment of a petal.
The quite common streaking of a contrasting color on a petal, considered a fault when judging, is a most welcome bit of genetic evidence if you are a breeder. Some varieties never do it, some do it often, and the Variegated types do it in every bloom. This is only likely to happen if the color that disappears is Simplex. There is a certain likelihood of damage, of course, due to chemicals and radiation, but significant additional frequency is determined by the genes position on the chromosome. The closer to an end where crossover tangling can occur, the more often the factor is accidentally lost an the higher the frequency of a particular change. If the resulting cells which carry such a change form sufficient tissue, then a cutting may be had and the change secured. This is so likely in the variegated types that such sports are NOT accepted for trial under the same rules as "regular" sports. Usually, however, just a few cells in a growing row on a petal show the effect and the result is simply a streaked and spoiled petal.
A breeder may wish to avoid such a flaw in selecting potential parents if it is the disappearing color that is desired for the offspring, but if the other color factors are of major interest, then one can be confident of their greater likelihood of inheritance. Thus the flaw becomes a benefit, and welcome evidence. Furthermore the very fact that streaking occurs proves the increased probability of complete loss of the simplex color and an increased chance for the grower to obtain a solid color sport.
Simplex losses easy to spot:
Harder to spot:
Most so called "whites" are actually ivory's with one or two alleles. They often also carry a simplex "A", which may or may not always show up as a pale lilac or pink flush. If you are experimentally minded you can test a doubtful "white" by placing it in a jar with a crumpled paper towel soaked in household ammonia. Ivory's will darken to some shade of yellow. A true white will not turn yellow. The white tips of bicolors are true white which is caused by a separate factor that suppresses all color.
I hope this article will encourage readers to inspect their blooms closely to observe the changes that I have described. Close attention is always a benefit, but you will be especially primed to spot any color sports which, as you will see, occur all the time.
While you are looking, give a little sniff to the bloom also. Sooner or later a new characteristic, such as fragrance, will show up. Of course it will be SIMPLEX and probably poorly expressed, but if it is there at all you will have a rare plant indeed AND the beginning of an exciting breeding program to intensify the effect. All truly new factors show up in this way; almost lost in the Dahlia's wealth of features and needing your sharp eye or nose to take our flower to its next level.
Many very interesting and potentially valuable sports are not saved because of the difficulty of taking Summer cuttings, especially late in the year on what may be a heavily disbudded plant. Since tip cuttings will probably not be available, you must be prepared to take a Split Stem Cutting. These are somewhat more difficult to root, but not too hard. This is what you do ...
Usually the stem below the flower that has sported will have had the top few side buds removed. That's too bad, because they were the most likely to also carry the changed character. However, the closest leaves (plus stem) that still have dormant shoots should be cut off. When you split the hollow stem vertically, between the leaves, you will have two cuttings, each consisting of an upper portion that can act as a handle, the important leaf-shoot bud, and the lower portion that WILL develop roots. Keep your fingers and their contaminating oils off of the lower portion.
Treat with a strong rooting hormone and insert into your favourite mix so that the leaf axil and bud are JUST below the surface, so that there is no possibility of drying. It may turn out that the leaf is quite large. If so, simply cut it back to a sensible size. Too much surface can require more water than the cutting can deliver - too little will not provide the energy needed to grow roots. It takes three or more weeks, but growth will start. Grow the plant on, but keep it potted. This plant will not make a tuber with eyes as there was no other node tissue - the only node grew into the plant. You must keep it in the house in a window or better yet under long day lights through the winter. Cut it back as hard and as often as you like (more cuttings!), but keep it growing. In the spring you take regular cuttings from this stock plant and they will grow normally and bloom and make a tuber.
Good luck! And be sure to let me know about your successes.
Another interesting family is the Cupid family of Ball formation.
Copyright © 1997 Wayne Holland
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