Using High Ploidy Roses can give Different Results

Just a bit of trivia

Next spring I intend to use two roses in my breeding cycle.

Rosa Sweginzowii and Rosa wilsoni, both are hexaploid and balanced 3+3. Crossing these with a modern type, would give completely different results for each and if fertile,the use of the F1 crosses would vary.

F1 Crosses

Rosa Sweginzowii(3+3) X Modern(2+2)Result Offspring(4+1)

Rosa Wilsoni (3+3) X Modern (2+2) Result Offspring(3+2)

All data used was from Hurst’s Septet Formulae

All moderns would be tetraploid, forgot to mention that



So… these hexaploids (assumed to be producing 3x gametes) crossed with modern tetraploids (assumed to be producing 2x gametes) will result in pentaploids.

3+2 = 5

Is that what you are saying?

Is it possible that the splitting in the precursor sex cells may less frequently not be even for both the hexaploid and the tetraploid.

There have been documented cases where unexpected ploidies occur, like diploid + tetraploid ----> tetraploid offspring etc etc etc.


The hexaploids were tested by Hurst and were shown to be both 3+3 . I use it when using species so I have a rough guide to what may happen theoretically. Hexaploid formulae can vary from 3+3, 4+2 and 5+1, what is important to me is the formula of the F1 cross, determining which path to go down.

You pointed out the diploid x tetraploid , resulting in a tetraploid offspring, Muriel was that offspring, but when Muriel was later crossed with other tetraploids it produced triploids.Something similar may have happened to the R. Bracteata as with the RugosaX used that resulted in producing R. Kordesii. It may have been the result of an environmental change, extremely cold winter or may be other factors (drift from herbicides).

Ploidy in rose breeding seems a highly complex subject, I really don’t fully get it.

Do you have an asprin, it gives me a headache lol

I don’t bother with it any more. Not that I am a real up and coming rose breeder, as such LOL. Still, if Mr Moore supposedly never bothered with it, I figure I’ll just do the same as he did. It is a cop out of sorts I know, but yes, it saves on the asprin round here. I give up wth it.


I think of this way:

There is a likely pattern of events that is likely to take place given certain actions and scenarios. However, these events are not static, and neither is nature. So its good to be aware of what may be going on, but its also good to let go (mentally) of any fixed ideas of how something will work. That is why I rarely plan out too far in advance even though I could. I try to make he best decision possible and move forward with it. If it fails, there are a lot of other ideas to focus on.


I like the idea of using hexaploids in our breading programs. Several years ago I used R.moyesii

R. moyesii ‘Geranium’ is virtually sterile? Now ya tell me! I have it on order for this spring and had big plans.

That is what another member told me and from my results it wouldn’t surprise me. I would go ahead and use it anyway, maybe you’ll have better luck than we did. I had R.moyesii “Highdownses” for a while and it wasn’t hardy enough to leave enough stem to flower from and it got BS so bad it was bare sticks for most of the summer. But it is a cross with a Hybrid Tea and Geranium may perform better because it’s considered pure R.moyessii.

Thanks for that Paul, I stumbled across Hurst’s work years ago, and only use it as a guide, I was aware it was written back in the 1920’s , but getting some direction even though the compass needle may be a little wonky still helps.

The interesting thing about R. Sweginzowii is, no body,so far has 'nt used it in a breeding cycle. Have about 30 seeds from a cross in stratification at the moment, will be interesting.

Some one was trying to get me to use R. Moyesii ( geranium) in a breeding cycle, glad I didnt get it in, have used Nevada with good results though.

cheers warren

oooops big correction, have 30 seeds in stratification from a cross with R. Forrestiana, but I am still wondering why nobody has used it?.

I think there are two reasons why R. Sweginzowii hasn

As a matter of interest, is it just the caninae section which have these univalents, or do other rose species also have these?

Also about univalent chromosomes in the dog roses, are they chromosomes which the plants use to transcribe from, or are they genetically inactive chromosomes?

is it just the caninae section which have these univalents

Interesting question. AFAIK the canina are the only group which has that unique meiosis.

Nature likes even numbers of chromosomes - odd numbers give unstable mismatches. The theory is that canina meiosis evolved as a means to accommodate sexual reproduction of a rose species (proto-canina) having odd numbers of chromosomes.

When we create a situation where chromosomal mis-matches are bound to occur we can expect something unusual has happened if it results in a living plant. Crosses between distant species (‘wide crosses’) and crosses between roses of different ploidy create such situations. The thought is that in such cases all or part of the ‘odd’ dna is lost or switched off but it would not surprise me to find hybrids where univalents get created instead.

Target breeding using caninae seems a daunting proposition. However, here are some traits and their inheritance patterns in caninae that may be useful in planning such crosses.


leaves - hairs and odorant glands

leaflet shape

epicuticular waxes

flower volatiles

peak flowering time

sepal size and serration

hip form and size

molecular markers


fruits - sepal persistence and the diameter of the orifice

shape and quantity of prickles


leaves: leaf shape in R. villosa x R. sherardii

Flower colour and size

hip shape

This may be enough information to make some predictions. For instance, I’m trying for pine scented moss by putting moss pollens on R. glutinosa.

Note, too, that flower color isn’t strictly dominated by the canina chromosomes. That is to say, you can expect to breed some unique colors with them if you try.

Reference: Wisemann, V and Ritz, CM. “Evolutionary patterns and processes in the genus Rosa (Rosaceae) and their implications for host-parasite co-evolution.” Pl. Syst. Evol. 266: 79-89 (2007).

I realized by using high ploidy roses would not be an easy task, but just think if you could find a way, it would be like opening Pandora’s box. This is what I think of when using cultivars or species which have’nt been used due to its difficulty or scarcity. The most important thing is , to find a good bridging rose to do it with.