Diploid vs Tetraploid - a crossroads

I’ve been reading and gotten myself in a loop. I know there are people with far more scientific/technical understanding and familiarity here than I do so just looking for opinions/thoughts.

Being in Australia, a generally favourable climate except those few weeks or summer with 40C+/100F+ temps. I’ve been looking more at the warmer climate species and classes and well diploids seem the norm. Add in a lot of references to resistance to PM (something I’ve been getting a lot of…don’t need Fedtschenkoana to make ghostly foliage here) and I’m left wondering what are the real pro/cons of diploid vs tetraploid?

diploids = more frequent cross over
diploid = higher rate of expressing recessive traits
tetraploids = thicker parts

I would assume tetraploids have more complex/dense pigment and perfume simply due to cells having more going on in them.

Mostly just wondering why tetraploid dominates the work being done, may just be the whole “breeding back to the current best” thing at play but I feel like I’m missing something.

Thank you

My best guess, thinking of some other species that have been recently advanced by intensive breeding is that tetraploids have certain features that are advantageous in rapid reproduction/propagation for retail trade. Daylilies, iris, napa cabbage(which may have hybrid vigor being an allotetraploid) just pop into mind at the moment.

There is also what evolutionists call contingency. Kind of like an accident that send you down one road rather than another. Really most of the big breeding programs with roses have been in the last 150 years. How many generations is it from Austrian copper (or Persian yellow) to PEACE? The rose used to generate a yellow HT depended on HP background for repeat blooming. If the mutation of FLC happened in an ancestor of roses brought from China, what other choice of parent was there if one wanted repeat-flowering HT or HP roses? So despite being an impediment to getting homozygous FLC mutant which promotes free repeating, tetraploidy was about the only option. van Fleet made a triploid with diploid wichurana that certainly doesn’t lack vigor. But repeated crossing and selection gives tetraploid offspring. Even fewer generations occurred between New Dawn (a sport) and most of the descendants.

Once there were some good colors, and good plant and flower form, competitive commerce drove the use of whatever could produce the fastest production of novelties, even before patents demanded it. Crossing the FLC mutation into diploids was very hard by classical genetic methods. It adds generations to the selection process.

Florist roses, pesticides, fungicides, fashions and styles constantly pushed work with the already well-positioned tetraploids to make novelties for teh insatiable market.

I hope someone can argue me out of this sort of fatalist position. Actually I’m optimistic that giving up pesticides and insecticides will drive the market in different directions. Plus application of CRISPR technology ought to soon allow us to get FLC mutants at will in diploid or tetraploid species. The issues are two. Actually doing it (selection), and successful plant regeneration. I would bet on floral dip being easier than callus tissue regeneration if we work with species that have large numbers of seeds per flower. Our stumbling block may be concern that the outcome could be labeled GMO.

The end of the opening paragraph is a bit…questionable. Polyploidy for daylilies comes at a cost, significantly reduced seed set (often around 6 seed per tet cross but over 30 per dip cross) so advantageous reproduction possibly not. The flowers are generally more showy/larger/thicker with tets but both tet and dips are still intentionally bred, tet’s don’t do the Spider/UFO form well due to the thicker petals and pink (at least currently) works better in the dips. I can’t really comment on iris too much, the bearded don’t grow here well (they rot so easily), the non bearded classes (Lousiana, Pacific Coast, Siberbian,etc) are predominantly diploid though (there are a few tet lousiana and siberbian but they aren’t the standard or where breeders seem to be working) but that market is far tinier…Tomas Tamberg has demonstrated some significant benefits in going tetraploid with non beardeds (fertile offspring from wide crosses, would open up warmer/humid climates than beardeds…just probably take a hundred years of breeding to look as equally interesting as beardeds currently are and to select for fragrance from the few non bearded species with it) but no one really seems to be working on that (possibly because it’d probably take more than 1 life time).

New Dawn seems to have been primarily bred back to HT’s and a few Floribunda, can’t really be surprised that tetraploid is the result, kind of an inevitability if always breeding back to tetraploid.

Between this and the other thread Diploidy or not diploidy. That is the question... - Rose Hybridizers Association Forum
I’m left thinking that tetraploid of the modern classes was more the result of breeding back to the best, chance and to retain cold hardiness (before the diploid cold tolerant species were considered) more than a significant advantages in being polyploid. I really feel like I’m on the outside looking in and something just isn’t clicking in my head :\

On a slight tangent though, I would assume at least in part that FLC incorporates juvenile blooming? Do polyanthas, tea, china’s, hybrid musks and noisettes (maybe?) not demonstrate juvenile blooming (I haven’t really dug around in those classes enough to know).

What is an FLC? Can we please define three-letter acronyms if we must use them? Thanks.

Sorry for the acronym if that’s the proper word. I wrote a long article on it in the newsletter a few years ago. It stands for Flowering locus C in the model plant arabidopsis. In roses it has a different name I suppose, but the principle is the same. When normal it allows flowering only after a winter. When mutated, the plant flowers as soon as it has the energy, so every few leaves up the stem. Probably the mutation was noticed only once and all the interesting (repeat-blooming) roses are descended from that once event. No real proof but circumstantial evidence. IN the wild the progenitors of various classes of roses do not rebloom. Only in the last roughly 200 hundred years have we in the west had them. That includes the existing CV of noisette, polyantha, china, tea and musk that do rebloom. To get repeat flowering in New Dawn offspring they had to be crossed to repeat-blooming plants, or multi-generation blind selection had to be used. Being market-driven, breeders took the shorter path.

About daylily and iris reproduction I meant vegetative, not sexual. Bigger sturdier, faster growing for cultured gardens, not survival in natural conditions.

Sorry, out of time for now. Off to tennis.

To Plazbo. Yes you are correct. Tetraploids beget tets. So of course New Dawn x HT = tet. But if there had been reblooming dips, it would have given a lot of dips. It is my understanding that if one has a decent stable of dips and tets, one can make crosses to generate interesting trip offspring. And they are basically sterile so they become bloom machines. It has been commented on this board some years ago that some European breeders use that strategy to generate their most successful products. Certainly the KO roses are in much the same position re self-pollination, though I don’t quite understand the cause of that self-incompatibility.

So we are always juggling different needs when breeding for the market. Working with low fertility triploids is a real pain when less than 10 % of pollinations yield seed. Either you need a lot of plants and a lot of people, or a lot of years per person to get something. But in most rose plants repeat blooming tends to shut off once there is a significant hip load, whether dip or tet based.

Pick your pain.

Much of the earlier (19th century) breeding took place in relatively mild climates. Teas and Tea-Noisettes and Bourbon hybrids with Teas and Noisettes, were favored … along with the older classes that remained popular. But then came 1816, the year without a summer. And then the devastating winter of 1837/38. The tender varieties were not driven to extinction, but their popularity faded just a bit. The hardier derivatives of Gallicas and Damasks crossed with the reblooming types became favored. That some of these were larger than Gallicas, as fragrant as Damasks, and as free-blooming as Bourbons made the emerging Hybrid Perpetual class a winning combination. Exhibition blooms on plants that rebloomed … more or less.

Later, after much hand-wringing, the HTs became recognized as a class that was neither HP nor Tea. The Shows made these popular even after the Floribundas emerged as (generally) superior garden plants.

Juvenile blooming is independent of the “gene for rebloom”.

De Vries: Juvenility in HT Roses (1976)

De Vries, Dubois: Juvenile Period in HT Roses (1977)

I understand the progression to higher ploidy, it’s like entropy.

Would a chromosome doubled diploid species still be fertile?

And I don’t yet understand the fertility of tetraploids after a few generations. For example Max Graf
R. rugosa × R. wichuraiana, too incompatible for meiosis.
R. kordesii an allotetraploid of the above should be and is fully fertile.
But what happens when R. kordesii is crossed with other roses? I’d bet it was tough at first.

Do fertile tetraploid modern roses carry at least one pair of chromosomes that match up with each other when it’s time for meiosis?

Take fertile Hybrid Teas for an example:
Is there perhaps a fully settled set of chromosomes from a combination of R. fedtschenkoana, Rosa moschata, R. gallica, and R. chinensis, that allow at least half of them to pair up orderly? Otherwise, I see complete chaos during meiosis resulting in infertility, And if the fertile moderns do carry that common set on one half, how can we use that knowledge to our advantage?

And if you are big time, how could you use that knowledge to protect your IP?

I love roses, the more I learn, the less I know.

Doubled diploids typically lose some fertility. I don’t have the reference handy, but C. D. Darlington mentioned (somewhere) that in his experience newly formed auto-tetraploids always have at least one unpaired chromosome, along pairs and groups of three or four. This does get sorted out in later generations.

And then we get into another bit of weirdness that was formerly describe as Wichura-type hybrids, because Max Wichura found some of this behavior among his willow hybrids.

For instance, if you mate a tetraploid form of Wichuraiana with the tetraploid Macrophylla var. Korolkowii, at meiosis the hybrids will usually present 7 pairs of Wichuraiana and 7 pairs of Macrophylla chromosomes. There will be little or no obvious segregation in later generations.

This is interesting, usually on the deep dives through threads of old on here it’s implied if a seedling has juvenile bloom it’ll be a rebloomer. Haven’t paid attention to it with my own seedlings, will going forward.

Back to my original point of this thread though…there doesn’t seem to be an exact consensus on pros/cons for either dip/tet, a few generalities but they aren’t universal as exceptions exist and often those exceptions seem to be in plant classes I was already looking at like rugosa and it’s thicker leaves/stems (compared to many other dips). With other popular garden plants (ie bearded iris, liliums, daylilies, gladiolus, etc) there’s usually some significant differences between dip/tet (granted a lot of it has to do with breeding and many years of selection) so when I started looking at roses I automatically overlooked the diploids until I started looking at traits not really in the modern classes like rugose leaves, foliage fragrance, cresting, extreme flower clusters like R. helenae/R. multiflora/etc and see a lot of interesting things in other ploidies.

So I’ve been looking at it as a case of “do I attempt to introgress the traits I like into the modern class genome or do I attempt to introgress the modern traits I like into the closer to species plants”. Either way I’ll be producing triploids so the question of what to put the triploid pollen on is where I go around in circles a bit. I’m leaning heavily to the second option as it seems especially with rugose foliage that it dilutes/disappears easily (on that front I wish Simon was still around, he seems MIA, I know he did a number of Scabrosa x mini would be interested to know what happened there and if there were any further generations made) so if I want to maintain that trait I likely need to stick within a generation from roses displaying that trait. Most people seem to be going the first way with introgressing diploids/species into moderns though, it makes me second guess what I’m thinking, I’m a hobbyist, I don’t have a background in this at all (software engineer though) if what I’m thinking made sense surely others would be doing it right?

The only trait I have doubts about taking down to diploid level is cresting. Based on things said on the forum it seems its a trait that gets exaggerated by more copies of the gene causing it. I know with Moores work there was a lot of health issues and nothing has quite reached the extreme cresting of Crested Moss itself so it’s likely not a question anyone can answer. I’m also not using one of Moores crested roses (using Helga Brauer) so there may be some points of difference in genes/chromosomes taken from Crested Moss.

this would be a lot easier if the traits I like weren’t so diverse and spread out :\ But I do feel more comfortable in travelling the diploid path and that I’m not missing something obvious since nothing major has come up.

I think that you will have to live through he triploid stage. Looks like a diploid trait will be harder to move to tetraploids than the other way round. It ought to be easier to bring repeat blooming to diploids than to take rugose foliage to tetraploids.

I did a quick google search on tetraploid infertility and hit a lot of articles, some very old, suggesting that any crop where the grain is the product of interest the autotetraploids yield much less than the starting diploids. Largely it may be caused by poor meiosis and mitosis during germ cell production so there are fewer seeds per head. But even earlier, fewer tillers per plant in barley for instance (Evans and Rahman). Darlington did say some about this in a paper at the bulbnrose site. Even crops where grain isn’t the target, the autotetraploid may be less good, for instance kale. That may be an indirect effect of scrambled and biased chromosome crossing over in the generations leading to the seed used to grow the crop.

Now I’ll have to do some more searching to refresh my memory on a couple of points.

For one, I vaguely recall reading that new tetraploid daylilies tend to be brittle. Triploids had the desired increase in size, but without the brittleness.

And there was something about triploid sugar beets, but the memory feels like it goes back some 40 years, and I can’t pull out the details.

Anecdotally, Basye’s Amphidiploid 86-3, a created tetraploid hybrid between Banksiae and Laevigata, is nearly a mule to work with. I forget who shared it with me eons ago with the warning that it won’t cross, and it has taken MANY years to get results from it, but it has finally worked. The greatest number and most promising results have come from using it with fertile triploids. Cal Poly X 86-3 'CPX86-3' Rose ; Golden Horizon X 86-3 'GHX86-3' Rose ; Lynnie X 86-3 'Lynnie863' Rose are listed on Help Me Find. L56-1 X 86-3 has resulted in three seedlings. One is quite weak, won’t grow and has yet to flower after three years. One is moderately vigorous with smaller foliage, smaller flowers (white with pink staining on the petal edges) and one is a monster, with large, dark, glossy foliage; single, larger white with pink staining flowers and appears to want to repeat. It is aborting hips right and left, which may be its character or due to the immaturity of the plant. Hopefully, the pollen might work.
The Lynnie X 86-3 seedling is quite fertile, both directions, but its offspring gives a mixed bag of traits. The more promising looking are using its pollen on Pretty Lady, resulting in what appear to want to be larger, arching shrubs which resemble Pretty Lady in varying colors from blush pink to coral.

My hunch is that with tetraploid and higher ploidy species roses things are probably orderly during meiosis, with settled sets of pairs representing a high degree of influence of particular ancestors finding each other. With jumbled up moderns who knows? I guess it could be a free for all. That could be why quite a few show poor hip fertility. I quizzed Dr. Byrne at A&M on this and he was a bit non-committal, although he backed up Kim’ by telling me that some induced tetraploids of diploid species crosses that you assume would be fully fertile turn out not to be, and he said that he is still regularly surprised by roses and mother nature.

The sterility of the tetraploid hybrid between Banksiae and Laevigata is certainly interesting. It seems to violate Darlington’s Rule, which is not a Law.

Diploid wheat has 7 pairs of chromosomes, just like Rosa wichuraiana. Even if we could get 7 pairs of wheat chromosomes and 7 pairs of Wichuraiana chromosomes into the same cell, we would not expect the result to be fertile even if the meiosis were regular. In fact, we would not likely get beyond the tissue culture stage with such a monstrosity. In this case the problem is not about failure of chromosome pairing, as in the case of hybrids of less remote relatives.

In some cases of weak fertility in distant hybrids, the use of trace elements, auxins and such like have helped restore at least a bit of fertility. In other cases temperature can make a great difference.

This paper deals with wheat hybrids, but might give some hints as to how the tetraploid hybrid between Banksiae and Laevigata might be nudged towards more fertility.