rookiequestion about -ploids


I was reading something about diploids, triploids, tetraploids, pentaploids and hexaploids. It’s all difficult stuff but is their any way to see on a rose what kind of diploid it is? Does every kind of ploid has specific visable characteristic? Or is it only visible by microscope?



Hi Timothy,

It is primarily visible by just microcope- counting chromosomes in specially prepared cells or estimating chromosome number from pollen size. However, one can have pretty good guesses knowing types of roses and becoming familiar of what is typical for them. For instance, roses that set few op hips that tend to have just one or a few seeds inside is a good clue that the rose may be triploid. This is the case for all the Knock Out roses, Home Run, Iceberg, Nearly Wild, many of the Meidiland landscape roses and so on. Most relatively fertile (especially female fertile) modern hybrid teas, miniatures, floribundas and shrub roses are tetraploid. Within the same genetic background you can typically see slower growth and less flowers, but thicker plant parts in the higher ploidy level roses. I found this for the polyantha roses I took from diploid to tetraploid with a chemical called trifluralin. People often say higher ploidy level plants have greater vigor, I don’t typically see this and think people are not being very articulate and when they say that are mixing the idea together of greater vigor with greater plant part size. There are of course very vigorous tetraploids and such and weakly growing diploids, but for generalities it seems the higher the ploidy growth slows down somewhat.

I suggest that if you have particular roses in mind to ask what the ploidy is and many of us may know.



Now that we’re on this topic, David, perhaps you can help me understand something else…looking at roses, it’s possible to cross diploids with tetraploids that may result in triploid offspring, but when it comes to breeding daylilies, I was informed that 99% of the time you cannot cross a diploid with a tetraploid and get a seed pod; “diploid and tetraploid daylilies are not compatible, and if a pod did develop it would be very very unusual”.

So why is all this possible with roses and not with daylilies?

Hi David,

Thanks for the reply!

I’ve crossed a lot with New Dawn last year (also this year) and i didn’t get much seed from it. The hips stay small to. Also their where a few OP fruits left on the plant. I get only 4/5 seeds per fruit. So this could be a triploid?

2 seeds of my New Dawn x Together Forever still growing but doesn’t have blooms yet. i’ll take some pictures when they grow.

Is their a simple diagram where I can find which combination will work the best and which is worse


triploid + hexaploid = not so good idea

tetraploid + diploid = winner


Many regards,


Hi Dee,

That’s a great question why diploid and tetraploid roses can cross more readily than daylilies to produce triploids. There are also some barriers in roses too, but to a less of an enough of a degree that we can get offspring. Some of the manuscripts by the French researchers that looked at ploidy among seedlings from crosses of haploids (2x) from modern 4x hybrid tea roses crossed with species and such suggest that there are gametes that are more likely to result in viable offspring due to their ploidy contributions. I worked with potatoes and there is a strong “Triploid Block” there. In potatoes and maybe with daylilies and other such species, one critical failure point is the development of viable endosperm. THere are embryos, but without the nutrition from the endosperm, they fail and die. One can try to save the embryos at a young stage in tissue culture and raise them to maturity. We did this in potato.

New Dawn is triploid. I raised a number of op seedlings of it this spring. One time bloomers or stingy bloomers with long canes is common and I think that does not have to due with ploidy. I have some seedlings that repeat bloom pretty good though too. It would be interesting to see what ploidy your offspring are. New Dawn is such a disease resistant rose it would be great to see what other wonderful progeny breeders can generate with it.



Interesting you mention that, David, because a breeder of oriental lilies in the area once mentioned that a few Orienpets (oriental x trumpet lilies) have been developed in the manner you speak of; they salvage the embryos before they perish, and raise them in petri dishes.

What I find bizarre is that a diploid rose that rarely sets seed may one day (years down the line) self-fertilize and produce fertile tetraploid offspring - now how freaky is that?? I guess there are no set rules when it comes to roses; they do have that element of surprise! I’m guessing this is an evolutionary thing. According to the writings of Dr. Svejda in a recent NRC journal, r. kordesii sprung from a ‘selfed’ Max Graf fifteen years down the line, if I remember correctly. So I learned that a reluctant or sterile diploid is capable of ‘selfing’ to producing fertile tetraploid offspring on a whim. Roses are quite complex, unpredictable, and quirky that way.

There is a 60 year old (40 foot long) Dorothy Perkins growing wild at my friend’s grandparents’ farm in south-western Ontario. I drove down there recently to have a look. There were but two blown flowers left on the bush holding on for dear life until I got there. I took some time to study this wonderful bush - it was evident it spread via underground runners all these years since there were absolutely no o/p hips to speak of. I also remarked very small, poorly developed stigmas; a friend of mine said it’s triploid, which explained alot. Could you say, David, if a TRIPLOID is capable of ‘selfing’ to produce fertile tetraploid offspring (in the way that diploid Max Graf produced r. kordesii)??

There are Dorothy Perkins descendants listed on HMF, mostly the result of it being a pollen donor, yet some of its offspring are curiously derived from it having functioned as seed parent, go figure! I took a runner with me to plant up north - this rose has the most charming clear pink flowers with beautiful rose veining and strong damask-like fragrance. I wonder if anyone here might have worked with it in any way?

Are you sure that is Dorothy Perkins? I still have a functioning nose, and I’ve not been able to find much (if any) fragrance in Dorothy’s flowers. I know that soil and temperature can make some difference in fragrance and (especially) color, but I’ve never heard that Dorothy has a strong fragrance of any kind, let alone damask or damask-like. Do you have pictures?



diploids should be the hip parent… many breeders have said.

Although, Ralph Moore has produced a few splended rugosa hybrids as pollen parents… and one is supposedly fertile (but not in commerce in the United States… in Italy, yes, but not here.)

When I use diploids such as Champney’s Pink Clusters, The Fairy, and Perle d’Or… they are nearly always hip parents. (I can’t get Renae to set hips, and so I use it as a pollen parent instead and have a rather nice polyantha like rose with old garden rose form and few thorns. Hip parent was Sutter’s Gold… it hasn’t been fertile because of lack of pollen… and perhaps ploidy number.)

Peter, we’re almost sure it’s Dorothy Perkins, or at least we like to pretend it is, lol! For the longest time, this rose was referred to as “the wild rose down at the farm”, until we asked my friend’s mom what kind of roses his grandmother had planted back in 1947, and she said she remembered a couple of them being Dorothy Perkins. There’s a chance it might not be Dorothy, but it looks pretty darn close. The thing that puzzles me is that HMF lists it as “non fragrant”. The blooms of this rose are semi-double to double measuring 2" across; it has prominent pink veining on the petals, and we all took in their wonderful fragrance. It has 7 light to medium green leaflets with matt texture. New runners (and young foliage) are a beautiful light green with many prickles that are long, thin, slightly point downward, and hooked at the tips. New runners also tend to be more stiff and upright than flexible. This rose is planted right in the heart of Ontario’s farmland, so the soil there is dark and fertile. I do have pictures, but I didn’t take them with a digital, unfortunately. I might put them on disc at some point just to oblige you. All I can say is that this rose looks almost identical to the one on HMF, with the exceptions being the fragrance and height. Its ‘rambling habit’ is more arching and spreading, if anything, with 6 - 7’ tall canes. It’s thickest canes tend to be more upright, and branches out at the top carrying clusters of pink flowers. For a supposedly “wild rose” it certainly does not produce o/p hip, but I do think, however, its pollen may be of possible use.

If you have pictures to post of your Dorothy Perkins that illustrates the flower, stems, foliage, and color in detail, I might be able to assess the differences. HMF doesn’t give me enough detail.

Dorothy Perkins (Syn. Excelsa) is a diploid.

When you make interploidy crosses you better think of wat ploidy to expect in the gametes. Then you can calculate ploidy in the offspring. Like a triploid (3x)(better use them as a male parent) will have haploid (x) and diploid (2x) pollen (you can see it in the sizes). So when you do 2x X 3x you will find mostly 2x in the offspring, while 4x X 3x will give 4x in the offspring. Sometimes you will find other ploidy numbers suggesting that sometimes you have unreduced gametes leading to higher ploidy numbers.

David, we again checked the ploidy level of Bonica (Meidomonac) with the flow cytometer as some time ago you obtained different results. It is here again tetraploid aswell in the leaves as in the roots we took from some cuttings to be better able to compare it with your chromosome counts.

Why are some triploids fertile/semi-fertile (New Dawn) and other triploids (Sir Thomas Lipton) are sterile?

Hi Leen,

It is great to hear from you. That is good you were able to confirm your Bonica is a tetraploid. The one I worked with is from Bailey Nurseries and was own root. It and also Royal Bonica, it’s reported sport were triploid. I confirmed Bonica again and it was still triploid. Dr. Huey the common US rootstock is triploid, but they were own root. It would be interesting to compare the different roses sold as Bonica and see if if they differ in appearance. In one of the earlier flow cytometry papers with roses (Yokoyo et al I think) they suggested that sometimes DNA content can be misleading and a couple roses were misclassified. Perhaps Bonica has more DNA typical for a triploid and the DNA content you are getting for it is consistent with tetraploids, but if a root tip squash or meristematic cells from the shoot tip were assessed it would have 21 chromosomes.

I suspect that with roses with relatively low fertility that the environment can play a significant role as well as perhaps physiological state for how fertile the rose is from year to year. I think another strong factor is having pollinators and relatively compatible roses to cross the nearly sterile roses with.

I think that the evidence strongly points to R. x kordesii not being a self of Max Graf, but a cross with another rose. Single flowers are recessive to more than 5 petals. R. x kordesii is semidouble to double and Max Graf is single. My suspicion is that Max Graf had a 2n egg and that flower was pollinated by some nearby double flowered tetraploid garden rose. Perhaps Kordes selfed the flower, but the successful pollen grain most likely was brought by some pollinator to generate R. x kordesii. I have a few Max Graf plants and over the years routinely harvest 30-40hips from them with 1-3 seeds each inside. I have Explorer roses nearby and polyanthas. Some years I pollinate open flowers with bulked pollen from tetraploids. I have a couple double flowered 4x seedlings with what may be John Davis which is nearby as well as a double magenta diploid seedling likely crossed with a nearby polyantha.

Sir Thomas Lipton is diploid.

A friend has what I suspect is a White Dorothy Perkins. It is in isolation and last year set just a few small op hips. This year I pollinated it with pollen from diploids and it has a lot more hips on it with greater size, although nothing like the hip set of a very fertile rose.

I think that as we are creative and persistent we can generate seedlings from challenging, but worthwhile parents and hopefully continue our work with more fertile selections bearing their genes. I have a nice Lilian Gibson (it is diploid) seedling that is also diploid and may be a cross with a nearby polyantha that is a lot more fertile.

Ploidy and fertility is very interesting for us as breeders. It would be great if we can all find access to a microscope and try to answer the questions we generate.




Thank you for the great information and for correcting my thought about Sir Thomas Lipton’s ploidy. Is my memory right that STL doesn’t set seed either by self pollination or foreign pollen? If I’m remembering right, could someone explain why a diploid would be sterile? Thanks for all the great information.



“why a diploid would be sterile?”

It is called genetical disharmony.

In other words in its set there are not the needed genes for seed development or more probably there is an incompatibility between its two genes sets when it comes to developing seeds.

Not uncommon with species crosses.

So much it is named interspecific sterility.

Hi Rob,

Like Pierre mentioned, there can be some genetic confusion. The parents are diverse enough that the genes and their cues for when and how to express themselves can be different enough that there is confusion and failure of things to progress well. This may influence chromosome pairing and many other traits. For instance the Grootendorst roses have frilled petal edges and a rather chlorotic appearance most of the time and I think that is probably due to genetic confusion or incongruity. Staying at one ploidy level does not ensure fertility. For instance, crossing a diploid donkey and a diploid horse makes a sterile diploid mule.

Sometimes part of the failure is that chromosomes have a hard time recognizing their partners for smooth pairing during meiosis and sex cells are left with mix matches and incomplete sets of the different chromosomes (aneuploid gametes). Sometimes chromosome doubling can help with that. So for STL perhaps after chromosome doubling the two sets of rugosa chromosomes can find each other and pair and the other background (a polyantha?) too. In wide lily crosses such as Easter lily x Asiatic lily crosses chromosome doubling does this well. In fact, the Easter lily chromosomes and Asiatic lily chromosomes preferentially pair so consistently without crossing over between genetic backgrounds for many chromosome doubled hybrids that selfed seedlings end up in essence breeding true and are just like the parent. This is what I heard happened with the Profusion zinnias. They are crosses between Zinnia angustifolia and Zinnia elegans and that diploid hybrid chromosome doubled to make a tetraploid. Selfing is somehow possible in these tetraploids now and they breed true because each species parent preferentially pairs and because of chromosome doubling the two copies of each species parents contribution and what pairs in the tetraploid are identical.

In our modern tetraploid roses there is so much variability in the species contributions and backgrounds. For each chromosome (roses have a basic set of 7 that contain all genes necessary for life) there may be more or less homology and ability to pair during meiosis. Maybe for chromosome one for instance the chromosomes recognize each other well, but maybe not for two. Those roses that are better able to have chromosomes pair uniformly (disomic pairing in particular, two at a time) seem to have better fertility. There are some papers out there looking at pairing of chromosomes during meiosis in tetraploid roses and there is a lot of variability for how chromosomes pair and later the final fertility- two and two, different sections or arms of three chromosomes pairing and a lone one,… This can lead to unbalanced gametes with incomplete sets of chromosomes going to each daughter cell and then reduced fertility, just like in the case of triploids.

Fertility and all the factors contributing to it are fascinating.

I think it is good if we look at ploidy as one factor (generally a strong factor, but just one) and keep our eyes open for roses that give us opportunities to bridge valuable genes and traits to our new seedlings. It is fantastic Henry has a seedling of STL that seems to have allowed him to bridge genes from STL to new generations of his seedlings.



Thank you so much for the explanations Pierre and David. David, your explanation answered so many of the questions I’ve been wondering about and in an easy to understand manner. You are so right that fertility and all the factors contributing to it are fascinating. Another question if I may, in the case of STL where chromosomes may have a hard time recognizing their partners for smooth pairing during meiosis would that be limited to that particular cross the produced STL or would one expect genetic disharmony with most/all rugosa x polyantha crosses? I did read that Henry had a possible tetraploid STL sport(?)…or was that a fertile diploid seedling? Years ago I was excited about working with STL and never had any success getting hips to set. Now I know that I had little chance of that happening. Thanks again for taking the time to explain these things. It’s greatly appreciated.



Hi Rob,

That has been the case for me with rugosa x polyantha crosses. In the mid to late 1990’s I generated a lot of those crosses and had over 5,000 seed. Out of those about 2,500 germinated. They suffered greatly as young seedlings and died from what I have come to think was just incongruity. They grew to a certain size and were stunted and died. My other crosses grew fine. I tried changing pH using more expensive grow lights and on and on. Come spring only 100 were strong enough to plant out and over the years only about 5 were able to flower normally and were kept. One was frilled like a grootendorst. One was a nice sized single blush. The one with five narrow contorted magenta petals seems to be the most valuable. It sets a few hips. I’ve tried to germinate seeds each year and got a few to germinate, but not survive very well. One seemed pretty vigorous and then collapsed. Svejda also found low fertility in her rugosa x china crosses and relatively very few set hips.

Hopefully my “ugly duckling” will be a link to some more beautiful seedlings someday.




You certainly have tested the rugosa x polyantha cross! Would it be safe to assume that polyantha x rugosa probably would give the same sort of results? It’s great that you got at least one that shows some potential. I hope you get some good results from it.

Henry, if you read this, could you report on what you have from Sir Thomas Lipton (sport or seedling) and how it is working for you? I thought I remembered that you had a tetraploid sport, converted branch or fertile seedling but can’t remember exactly what it was. Thank you.



Just to make a correction here; Peter sent me detailed photos of the real Dorothy Perkins, and I’ve concluded that my rose in question is NOT Dorothy Perkins after all. So the Fortwich Rose remains a mystery until I’m able to have it identified. Thanks for everything, Peter; you made a huge difference, and David, too, for clearing up any misconceptions about r. kordesii.

If you have pics, I can try my best to ID it. Also, Roger’s Roses (google it) has a lot of pics of random ramblers. Maybe you have Debutante or Lady Gay, among many other bajillion of the Walsh rambers…