Can someone explain in layman’s (novice) terms about ploidy and it’s impact on hybridizing??



THat’s a great question John. Ploidy is assoiciated with fertility (not the only factor of course) and in my mind that it the main reason breeders are interested. For instance, if one tries to make crosses staying at the diploid level (two sets of chromosomes) or tetraploid level (four sets of chromosomes), the offspring generally should be somewhat fertile and one can keep moving on with their breeding objectives more smoothly. Triploids (three sets) often have reduced fertility as the sets of chromosomes don’t always divide nicely and incomplete sets of chromosomes to sex cells often results in unsuccessful gamates.

One can make crosses between tetraploid and diploid roses, but sometimes the rate of take is somewhat lower than staying within the same ploidy.

THere are lots of exceptions and these are just generalities.

Dosage also is something to consider. Paul Barden has shared that ‘Golden Angel’ offspring often takes on a lot of traits of the male parent and is therefore an interesting parent to provide a lot of diversity in the offspring. It is triploid and can act as a bridge in providing fertile diploid, tetraploid, and triploid offspring depending on what you cross it with and even mixes among the offspring are found. It may contribute one set of chromosomes or two sets (sometimes I suspect even 3).

Ploidy can also be a clue in some situations helping to identify a “mystery” rose or identify which species a wild rose is.

Ploidy is also an interesting thing to consider for growth rates. The lower the ploidy the faster the growth rate is typically. There is less DNA to replicate and the plant parts tend to be thinner, etc. THe higher the ploidy the slower the growth rate typically, less branching, thicker plant parts, etc. These are generalities, but as one has roses of the same genetic background at different ploidy levels it is clearer to see. My diploid and induced tetraploid polyanthas and rugosas definately show that as well as when I see the growth rate and habit of R. acicularis from 4 to 6 to 8x. It seems like many of the great landscape roses these days are triploid. It is a nice compromise for growth rate and flowering and plant part size/thickness. Triploidy also is associated with less fertility and therefore less fruit set and perhaps quicker repeat bloom as in essence they are deadheading themselves. So, ultimately trying for triploids is a strategy we can use, but recognize it may be more difficult to generate offspring from triploid parents.

Just some quick thoughts before I head to work.



I am intrigued with your comments: "The higher the ploidy the slower the growth rate typically, less branching, thicker parts, etc.

“My diploid and induced tetraploid polyanthas and rugosas definitely show that as well as when I see the growth rate and habit of R. acicularis from 4 to 6 to 8x.”

I had no idea that there is a difference in the growth rate and habit of the different ploidies of Rosa acicularis. Did you determine this yourself or has there been a previous reference to this by a researcher? Regardless, I’m going to pay more attention to this situation when I collect propagules of populations of this species.

Thank you for this important information, especially when I am going to be doing much more work this year with Rosa acicularis in breeding programs.

Hi Paul,

Great point. It is a general trend in polyploidization studies comparing the induced polyploids with the starting material and was the case in the polys and rugosas I doubled as well as the one R. setigera that was doubled too.

The ‘Kinistino’ (8x) R. acicularis you shared with me for counting has grown into the least branched, slowest growing, most thick, rounded leaved form of R. acicularis I have seen. The 6x form at the MN Landscape arboretum is more vigorous, etc. than ‘Kinistino’, and the 4x forms seem even more so. I think growing conditions and other factors would make it a bit difficult to confidently say something is this or that ploidy, but it can help and there seems to be a trend between ploidy and morphology.

It is easier to see when we compare within a limited gene pool and genetic diversity can make things more difficult to detect the influence of ploidy on morphology. For instance, rugosas seem to have such thick foliage etc. and are diploid and may seem to have more polyploid characteristics than a 4x rose of another class. However, when one compares a 2x and 4x rugosa the trend in morphology changes is seen pretty clearly. Rosa acicularis has a wide range, but it seems the trend holds up to some degree in the ones I’ve seen. Morphology differences is what led Joan Monteith to identify the 6x probably Rosa woodsii she found in a patch of 2x R. woodsii to know it was of higher ploidy and unusual.

Take Care,


I would love to see here some photos showing the physical changes that are induced by different ploidy on a single class (eg. rugosa or some other)!

Some of the larger briars like R. moyesii and the wing thorned rose grow like small trees, often making one large trunk and some smaller trunks when they are mature sized. It looks wicked cool in person, and feels amazing to be able to walk under one when inside a botanical garden setting.

Has anyone ever double Rosa wichurana itself? That would be interesting.

Well John I thought about your question and here is the best way I can give you an answer. Almost every type of organism has a certain natural state of ploidy (virus and some lower life forms have different rules but that is a whole different subject). The diploid number of chromosomes is the base level and then after we have names to denote other higher number of chromosomes.

So at the diploid level in roses we have 14 chromosomes (the number of chromosomes can be different depending on what organism your talking about so in humans it is 48 but this is still called the diploid state because this is the base number). So lets say for visualization state that the 14 chromosomes are represented by 14 shoes thus 7 pairs of shoes overall. When sex occurs between two diploid roses the new seedling has 7 left shoes coming from the mother and seven right shoes coming from the father giving the seedling 7 pairs of shoes. The 7 right shoes + the seven left shoes = 14 shoes overall is the base state or the diploid state in roses. This state where each shoe or chromosome has a match and this is what makes the plant happy and everything work out.

In general the different levels of chromosomes are based on adding a whole set to the base number. So Tetraploids have 28 chromosomes (shoes) which is 2 x 14 = 28. So a Hexaploids is 42 chromosomes (Shoes)which is 3 x 14 = 42. Sexual division in these work the same way as the diploid division except the number of shoes or chromosomes for each parent increases by seven or 14 overall.

Problems occur when the parents chromosome numbers do not match. Lets say our mother plant is Gloire des Polyantha which is a diploid (14 chromosomes overall or 7 pairs of shoes) and we are using the pollen from Commander Gillette (aka 65-626) which is a tetraploid (28 chromosomes or 14 pairs of shoes). The mother plant Gloire des Polyantha gives away to her new offspring seven right shoes and Commander Gillette gives to this offspring 14 left shoes). So this new seedling has seven pairs of shoes (the normal diploid number) but it also has 7 more left shoes coming from the father (7 + 14 = 21 this is what we call a triploid). This not only makes it hard to walk but when this new seedling has to give away it shoes to the next generation it usually does not know how to split up these seven shoes evenly.

Usually these odd states of ploidy like the triploid above means the plant is sterile. While it grows perfectly fine when it comes to sex it just can’t do this. But god has a sense of humor so to keep us humans on our toes he made these rules and then made exceptions roses being on of them. In roses the triploids are sterile just as in every other kind of plant except for this particular variety or that particular variety. So while most are infertile enough are fertile that it pays to try using a triploid at least once just to make sure god is not laughing at you.

So the basic levels of rose ploidy are

Diploids (14 chromosomes)

Tetraploids (28 chromosomes)

Hexaploids (42 chromosomes)

Then you got the

Triploids (21 chromosomes)

which falls between diploid and tetraploid on the scale

…And finally if God did not make it difficult enough you have the Caninae part of the rose family behaves on that part of the family I would suggest that you first understand the basic ploidy level and how they work and then when you feel comfortable then do a search on this forum using Caninae as a search word and then you will see God truly is laughing at us some times.

One last thing if you have a library card or can find this book up in the book store I would recommend the cartoon history of genetics. In goes through the history and basic genetics in an easy to understand format.

You’ve got me laughing too Adam! I’d never thought of them as shoes before, but that’s a great analogy.

And while I was reading that, I was thinking about sterile diploid hybrids… that could be like 7 left shoes trying to match up with 7 right army boots. Not similar enough, so confusion and sterility!

Ya it was the best way I could explain it. It doesn’t explain things like cross over and link genes but it is a good start.

Jadae, besides Eddie’s Crimson (which was used in the breeding of Knockout), do you know of other moyesii hybrids that make rose tree trunks?

Also, I was looking here and I noticed that a lot of the Rosa cinnamomea hybrids produce “petal-lets”:

The Rosa bracteata hybrids also seem to have a unique flower form.

About working with triploids. Has anyone else noticed that triploids seem to swing one way or another in the pollen they like to accept? In other words, some triploids seem to prefer diploid pollen and some seem to prefer tetraploid pollen?

Jon, the R. m. ‘Geranium’ at a place here called Joy Creek Nursery makes a small tree. They might have the straight species mixed in there, too. The nursery is basically a botanical display garden of rare plants that has a sales cottage. It’s the same concept as Heirlooms, but it regards all types of plants.

I wonder if this difference applies to plants?


Without doubts as long as plants are organisms…

Preamble of the text is about all organisms gene expression.

“Understanding how organisms function at the level of gene expression is becoming increasingly important for both ecological and evolutionary studies. It is evident that the diversity and complexity of organisms are not dependent solely on their number of genes, but also the variability in gene expression and gene interactions. Furthermore, slight differences in transcription control can fundamentally affect the fitness of the organism in a variable environment or during development.”

One could add it is main obstacle encountered by genes manipulators…

“In other words, some triploids seem to prefer diploid pollen and some seem to prefer tetraploid pollen?”

Yes, I’ve noted this tendency as well.