[1] set the stage. cover diploid,(a pair of chromosomes that both contribute to offspring character), in humans and reduction division to form reproductive cells, and recombination. then extend to the octoploid dahlia, with 4 pairs for each of 4 main color factors. History of B/Y tetraploid plus A/I tetraploid combination event.

[2] Symbols - B Y I A . Rules of expression. Dominance/recessive and upper case letters - mention recessive as equal to "blank". Cumulative regarding A and I, topping out, competition between factors. Numerical rules There is also a cumulative yellow inhibitor, H.

[3] Show complete genotype and simplified shorthand.

The following are two reproductive cells. Both are tetraploid and have half the genetic material of their parents.
BbbbaaaaYyyyIIIi pollen
bbbbaaaaYYyyiiii ovum (seed) When combined back into an octoploid new dahlia that combines ALL this information

However, BbbaaaaYYyyIIIi is how it is described, or shorter yet B1Y2I3, 
ignoring the fully recessive a's. This looks tetraploid, but it is a shorthand 
form which only shows the effective genes. For simplicity, we assume that the 
factors are all on separate chromosomes and that they are independently inherited,
but that is not correct and many are linked in any given cultivar.
Mutation events CAN separate them and this has happened in every case.

Possible reproductive cells (gametes) from this dahlia are:

[1] Bbbb : must get aaaa : must get one Y, could get another and yy : could get 1 or 2 or 3 I's plus i.
or
[2] bbbb : must get aaaa : must get one Y, could get another and yy : could get 1 or 2 or 3 I's plus i.

Thus this parent has 50% chance of passing on B, 0% of A, 100% of Y, 1/16 that no I's are passed, so 15/16 that at least one I is included. two or 3 I's are possible but less likely.

Whites are the key to tracking, if that is desired since they are blank for all colors. Thus breeding with them will give clear indications of the make up of the colored mate. This is a lot of work and it is complicated by the incompatibility between many dahlias. Lawrence did that work for the following table. This is a very long process, because there is a lot of incompatibility that seriously inhibits fertility between certain "families".

There may be more than two compatibility "families", but I have no data as yet. The sticky fluid on the stigma contains nutrient to support the process of pollen germination leading to fertilization. There are also hormones that inhibit self pollination and pollen from the same genetic "family". This means that a lot of crosses simply don't work, and no data can be obtained. The table below is a tremendous achievement.

Some colors associated with established, tested dahlia genotypes

magenta	A2 I1		scarlet	B1 Y2 I1
deep magenta	A1 Y1		scarlet	B1 Y2 I1-2
apricot-magenta	A2 Y1 I?		scarlet-orange	B2 A1 Y2 I3-4
apricot	A2 Y2 I?		dp scarlet-crimson	B2 Y1 I2
magenta	A3 I3		dp orange-scarlet	B2 Y2 I?
purple	B1 A2 I?	*	dp crimson-scarlet	B3-4 Y1 I?
dp purple-crimson	B1 I1	*	deep scarlet	B A? Y2 I?
pale purple	B1 I2	*	white	I1
rosy-purple	B2 I2	*	ivory	I2
crimson-scarlet	B1 Y1 I3-4		white	I2
crimson-scarlet	B2 A2 Y1 I1		yellow	Y1 I2
crimson-scarlet	B1 Y2 I?		yellow	Y2 I1
purplish-crimson	B1 Y1 I?		yellow	Y2 I2
purplish-crimson	B Y2 I?		yellow	Y3 I2

Information on a factor that is simplex can often be spotted by its loss in a random mutation causing a streak in a petal. See my article. On the other hand, a stable color that never streaks is pretty good evidence of multiple (2 or 3 or 4 ) factors that supply redundancy so that a loss mutation will not show.

*Numerical rules

Y = 9, B = 6. these are the heavyweights - from one tetraploid ancestor.
A = 0.5, I = 1.0 . obviously very different - from the other tetraploid ancestor.

Y and I produce apigenin and quertcerin.

Anthocyanin is produced whenever A or B is present, but exactly which chemical type AND color depends on some point addition. Cyanin - reddish, is produced when the point total is less than 8. Over 8 yields Pelargonin - purplish red. The Blue Delphinidin has never been found in dahlias, to my knowledge, but is chemically very similar and looks to be within a single mutation event, so there is hope.

Combinations of
Y and B = red, Y and A = apricot,
I and B = various purples, I and A interact and compete = whites, pinks, blends.
the H inhibitor of Y can cumulatively dilute its effect almost to I level.

Pigment production potential can only reach 2 unless Y and/or B is present when it can go to 6. Thus most combinations have genes demanding production of more pigment than the plant can actually produce, and competition and compromise occurs. There is also some evidence that cell sap pH is another genetic factor that can influence the hue of an anthocyanin. This is not influenced by soil pH.

Wayne Shantz and Gordie Leroux are both on the trail of a good violet purple cactus. Both are using Kenora Challenger which looks to be I1or2. Success will be some combination of B and I that exceeds 8 points, so that pelargonin(less reddish) is produced. My intuition is that this elusive color is B1 I3or4 = 9 - 10, with competition from the I's reducing the reddish expression of pelargonin. So I would suggest crossing Kenora Challenger with one of the * types in the table. The purple listed as - B1 A2 I? is interesting and suggests that including A might also be useful.

I will be releasing Hy Rudy B, B SC PR next year - 6.0 out of10 undisseminated, Ribboned as high as section, Blue in open at Eugene '97. I would estimate that it is B2 I2or3, and that it would make a great breeding mate, if compatible. It has broadly revolute petals that do not quill. Color is rosy purple with violet tones on petal reverse and tip.

And a good Ivory might be Hy Mom, an AA IC. Goes to TG 2000. Spike X Klondike.
You can see the depth and petal count.

---

Dark Foliage

My experiments suggest that Dark foliage - lets call it "D" - is dominant in a given pairing of chromosomes, but since there are 4 pairings it gets more complicated.

DD DD DD DD = full black leaves and calyx and stem and central disk. It would be the same as
Dd Dd Dd Dd, or any other genotype that had a "D" in each pairing. So simplifying, lets call all such =
D D D D or D4. Then we have acceptably dark ones with some green in the leaves with D D D d (D3). Those with D D d d (D2) are visibly lighter and need intense sunlight to develop much darkening. The simplex D d d d would only have a few hints showing. I refer to them in my notes to myself as Full Black, 3/4 Black, Half Black, and Maybe.

There may be more than one dark foliage pigment. Keith Hammett observed that there seems to be a more purple and a more bronze version.

Dark anthocyanin in blooms is closely linked to the foliage anthocyanin character, but Hammett has broken the link with Clarion, pure yellow single, which I just got last year. He has also released Midnight Sun, a soft orange Small Dec., about 4 - 5 foot, with D3 appearance. It has given me some hand pollinated seed that yielded several seedlings with some signs of dark foliage - D1 or D2. I attempted a backcross from and to them with Midnight Sun and have 2 seedlings showing D2. In breeding, recessives are actually a lot easier to deal with since they must be pure or they do not express.

I'm pretty much convinced that the Variegated character is inherited as an accumulating dominant in much the same way.

July 2003 Update

I have kept busy breeding various dark foliage types and, although the gene pool is limited, I have been able to observe for several years since the previous article was written. I summarized my findings in a letter to a correspondent in France who asked for clarification, and then to Keith Hammett for his comments. Letters, slightly edited, follow...

from me:Regarding Dark Foliage in the dahlia: My comments are based on my observations and I cannot PROVE the hypothesis. However I am convinced. Each succeeding cross adds new observations and they have all fit into the concept quite comfortably. Still not proof, but compelling.

Point #1
Dark factor is independent of Green. Green is always present.
Point #2
The dark is an added characteristic that forms a light activated pigment (Anthocyanin) in surface cell layers. Mostly on the leaf top surface. Mature leaves do not have it on the under side and light exposure will not cause it. Shading a leaf will cause the dark to be re-absorbed. Thus dark factor is caused by an additional genetically controlled new pigment.
Point #3
Most recessives are simply the lack of, or failure to produce some protein or enzyme etc... This dark factor actually produces something. Something new. Something additional. Actually the pigment is a familiar dahlia feature. The new part is expression in the leaves..

Point #4
I understand the temptation to rate it as recessive because of its reduction or disappearance when Dark is crossed with Normal Green. But that behavior is only easily explained in traditional Mendelian dominant/recessive terms if the species is Diploid. When it is composed of 4 matched pairs (octoploid), with each gamete tetraploid, then it becomes much more interesting as each factor has the potential to be expressed in steps. 4 steps. Actually 5 if you include no factor at all! Please take another look at my article (above) and perhaps I will have added some clarity to my idea.

However I can disprove the dark = recessive theory as it only takes one counter example to do that!

Crossing 2 recessives always gives recessives. yes? I have several incidents of dark X dark yielding green.

His reply:

I can see that you are refining your ideas with regard to the inheritance of
dark leaf dahlias.

I agree with the points that you make.

#1. Yes the pigment or pigments are clearly in addition to chlorophyll and
occur in the cell sap rather than in discrete plastids.

#2. Yes the pigments concerned are light sensitive. We need to know
precisely which pigments are involved and we need to know whether the
intensity of expression is a matter of balance between pigments which form
sequentially under the influence of light or whether it is a matter of
concentration of a specific pigment.

#3. Yes I guess recessives are most commonly something being turned off or
absent. The whole concept of recessives works OK with single Mendelian
genes in a diploid situation. The paradigm is clearly complicated with an
octaploid not to mention the possibility of polygenes.

My problem is that I don't think we can determine a model for inheritance
without a better understanding of the mechanisms which give us dark leaves.
If more than one pigment is involved we are in a polygene system. This
could involve different genes for different pigments or analogues of the
same pigment and might involve other genes which have an influence on the
concentration or determine in which cells the pigments are expressed. Often
with pigment expression in petals adjacent cells may express wildly
different pigments. Blue next to red or absent.

I think that we can agree that it is a complex phenomenon that can not be
explained by a simple model. I support your observation that dark x dark in
no way produces a population without greens.

My reply:

**since then I have been out and around my patch ranking the foliage of the dark parent seedlings. D0 no signs of pigment, D1 slight darkening, D2 general darkening, but still a dark green, D3 some very dark sections but green still evident., D4 virtually no green evident without a search. The D2/D3 call was difficult near the beginning, but then I realized that if the overall impression was black = D3, if the overall impression was green = D2.
D3 is a perfectly acceptable level given decent sun exposure which has been lovely this year. A 30+ day several weeks ago burned my darkest seedling and that raises another question mark as I had supposed the dark reflected damaging radiation..What about ionizing radiation. Do you have any info or instruments to test that?

I have 5 D0, 2 D1, 36 D2, 34 D3, 7 D4. All from D3 parents. 2 of the D0's are from a D3 X normal.

And a subsequent message from me:

The dark pigment does seem to absorb heat like an Anthocyanin should. I wonder if it is useful to the plant for any of the following.

1) dark seedlings are much less noticeable in the early going. Perhaps reduced predation?
2) possible ionizing radiation, like ultra violet, is absorbed. This would be useful at high altitudes where UV can be a killer.
3) Infra red absorption could add just enough heat at higher altitudes to extend the viable range.
4) toxicity? like the purple potatoe.

Any additional thoughts? (Any reader this far along is very much invited to comment!)

Copyright © 2003 Wayne Holland

email to nospam_hydahlia@shaw.ca just delete the nospam part!

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