I have been wondering if the inheritance of the repeat flowering trait in tetraploids is as cut and dry as in diploids? For example one could expect the offspring of two heterozygous diploid parents to break about 1/4 expressing the repeat gene, about half carrying the gene, and about 1/4 not carrying or expressing the trait. Do these type of results translate when working with tetraploids? Do the multiplication of the chromosomes involved in a given cross alter the statistical break down of a recessive trait being expressed?
This is the voice of an inexperienced novice. Any help would be appreciated.
You are correct; the multiplication of chromosomes does affect the statistical break down of a recessive trait being expressed. With a tetraploid there is four sets of chromosomes and usually only two are past on to next generation. If we look at the gene location responsible for repeat bloom and assign the dominant allele for non-repeat with a capital
Paul, thank you for the confirmation of what I suspected. If this is true of repeat blooming, it then follows that it would also be true of all recessive traits, both desirable and undesirable. From that info, it would seem that working with diploids is likely to give quicker positive results as the isolation of ANY given trait would be easier and accomplished with less effort.
it would seem that working with diploids is likely to give quicker positive results as the isolation of ANY given trait would be easier and accomplished with less effort
Sure, if your objective is to isolate a trait that happens to be available in a diploid rose, and it’s a trait that is dependent on a single gene (few are). However, it’s a bit like the dog who chases cars and finally catches one - what’s next? The fact is that it takes a very long time and a great deal of work to turn it into something desirable.
Great point!!! Roger Mitchell has written some great articles working with 4x species for RHA and his article on inheritance of juvenile recurrence for the issue of Floriculture and Ornamental Biotechnology. I’m definately not afraid of working with tetraploid one time blooming species. It just takes longer usually. They actually form the basis of many of my advanced breeding lines. I have some parents now finally that are one time bloomers and tetraploid, but have three copies of the repeat bloom allele- so Rrrr. When I cross them to repeat bloomers I get half repeat bloomers. A person just filters through the parents and finds some that have the other traits one wants (health, hardiness, etc.) and works towards repeat bloom at the same time. Step by step, generation by generation, we can build the germplasm we desire. One can just think of the earlier generations as parent building and later ones where you can get more repeat bloomers coming out and may want to raise out larger numbers tossing the one time bloomers early on knowing there is greater liklihood of getting more repeat bloomers that hopefully also possess other traits one wants.
I have a tetraploid that is RRrr for repeat bloom and in crosses with repeaters I don’t get the 1/6 repeaters expected. I suspect the RR chromosomes are preferentially pairing so each gamete gets Rr. Oh well, I’ll just have to go another generation to get Rrrr and hopefully then repeaters. I’ll work at selecting seedlings that are healthy, vigorous and have other traits I like along the way to hopefully preserve the positive traits in the original 4x species and why I started those breeding lines.
Moving in multiple steps isn’t so bad. Eventually we move closer to what we are looking for and can do so with our limited resources. It’s hard to believe I started breeding roses 25 years ago. We’ll all hopefully keep breeding roses for a long time to come, so investing in longer term goals isn’t so bad.
Wow, I didn’t realize there were that many barriers in the diploids. Is it better to stay with roses that have a similar septet formula? Are there many known hybrids or species that bridge compatibility well between one species and a dissimilar one?
I agree, with such slim odds of getting all the desired traits from a cross all in one shot, it is more practical to take it in steps. Like you say, going from
I didn’t mean to be discouraging about using diploids either, just cautionary about the investment it takes to work with them.
About the only thing I can add to the advice of Paul and David is to advise you to tightly focus on a specific objective related to the trait you are after. Learn everything you can about the trait through the scientific literature and especially by your own direct observations. Keep in mind that the genetic basis of vaguely defined ‘traits’ like disease resistance and winter hardiness are due to multiple genes and their heritability will be harder to pin down than more specific traits like, say, fringed stipules, the curve of a prickle or pubescent leaves. Likewise, there are more types of remontancy than the form of juvenile recurrance David and Paul have described, and these forms (and their interactions with other forms) are not as well characterized genetically.
Paul mentioned bridge species. This is a very important concept that has largely been ignored by rose breeders, at least in the published literature. The idea here is that roses (either species or hybrids) which are genetically intermediate between two other roses are best able to mediate the transfer of a trait between the two more distantly related roses. Helpmefind.com has a wealth of lineage data that is useful in this respect. However, for species roses you will also need to study phylogenetic charts for clues about possible bridge species.
I think concentrating on one specific trait is fine once you have the rest of the plant to point where you want it. If the plants you want to work with are close to what you want then go ahead work on the little traits. But if they are not then you have to get the plants to that point. Like Ralph Moore said and I
Thanks for the complement Paul :0). I started breeding roses when I was 13. One rose that I’ve found that seems to be a good diploid bridge is ‘Therese Bugnet’. It crosses back to rugosas to make rugosas with a more almost quartered flower form sometimes and one can get the shiney rugose foliage back in some. It crosses with polyanthas and makes some very interesting hardy polyantha like roses with larger flowers (like my ‘Catherine Guelda’ that won a silver certificate at the ARC trials a few years back). For a diploid it sure has a lot of potential.
With its wide background and multiple generations from direct species, I think that helps. THere is the idea of congruity backcrossing that Peter Ascher first named. Julie Overom wrote a very nice article on it in a past RHA newsletter issue. He demonstrated it in beans, but it can apply elsewhere too. Let’s say you have two species (say we will always work with diploids) that cross, but the offspring are basically sterile. Make the cross between different genotypes of the original species. Screen the offspring for some individuals with a little fertility. Work hard with them in order to cross them back to one of their species progenitors. Take these backcrosses and find those that have the most fertility and then backcross them to a member of the other species progenitor. After repeated backcrosses one direction and the other to the original species progenitors (can be different genotypes of that species) one eventually find individuals that have significantly more fertility. Such individuals serve as a good bridge to members of both species and then often to species that are different from those two.
The whole foundation is that one forces recombination between the two species as the seedlings go through meiosis and make their sex cells. Different sections and combinations of different species chromosomes are then reshuffled and individuals that have combinations that allow for greater fertility are possible. Even beyond that new traits often emerge. If one is just backcrossing only to one original parent and minimizing one original parent’s chromosomes, this process doesn’t seem to happen as readily. Peter got bean shapes and patterns emerge in advanced generations that were not present in the two species he started with. Who knows how much is locked up in the genomes of the plants we are working with and can be revealed.
I have some advanced generations of an annual bedding plant that I enjoy breeding where I incorporated a different species and intermated parents to keep a lot of both species genetics and encourage recombination. In these advanced generations I am getting prostrate growth habits emerging (I haven’t seen that in this bedding plant before- it’s not in either parent), interesting bicolor floral traits, etc. It is a lot of fun!!!
For my Ph.D. work I studied Easter lily (Lilium longiflorum) and its close relative L. formosanum. THere are seed hybrids on the market that bloom fast from seed like L. forosanum called L. x formolongi. I wanted to recreate these interspecific hybrids to study the inheritance of fast bloom. I couldn’t get viable F1 seed!!! I only was able to get some F1’s after embryo rescue and they were basically sterile. These seed strains I learned later from a Japanese breeder are several generations away from the original parents with selection for fertility and fast bloom along the way and flowers and leaves that look more like Easter Lily. These seed lines for sale are amazingly fertile and cross readily with both Easter Lily and L. formosanum. They also make great bridges to other lilies. I was able to generate some intersectional crosses with Oriental lilies with them using embryo rescue.
I don’t think we need to necessarily follow the congruity backcross system like a step by step process, just as long in the end we have enough divergent crosses to encourage a lot of recombination and then eventually select individuals that have usable fertility.
I have crosses with ‘Alba Meidiland’ (low fertility for me) with polyanthas that have just bloomed this spring and have lots of full-looking hips on them!! I also have a ‘Lilian Gibson’ x polyantha hybrid that has more fertility than LG. Raising seedlings from divergent hybrids like these with just a little fertility can be a way to generate offspring and find some that will hopefully be more fertile and serve as bridges to other germplasm groups.
What complicated advanced hybrids besides ‘Therese Bugnet’ have others found in roses that serve as a good bridge?
Although this is the first year I have had an opportunity to work with it, I am hoping ‘Suzanne’ will prove useful in this regard. I have found that ‘Basye’s Thornless’, aka ‘Commander Gillette’ breeds with just about anything, in both directions, and is half R. carolina.
I now working with some hybrids involving R. rugosa and R. bracteata that are fully remontant and fully fertile. I have a first generation R. clinophylla hybrid that is remontant also (how did THAT happen?) and sets seed easily. I have not yet determined if the seeds from this hybrid will germinate; I won’t know till next Spring.
When crossing little compatible diploids I got positive results using as many different individuals as possible. Mixed pollen of the sp on many mothers. Fertile hybrids being possibly better mothers than species. It is surprising and not so predictable that most successes are from a few mothers despite similar pedigree. As happened for me using bracteata x clinophylla as well as roxburghii pollen on fertile hybrids involving bracteata, rugosa, nitida and foliolosa.
I’ve read over this thread and have a better understanding of repeat bloom inheritance. Great information.
I was wondering about a seedling I have PMND which is ‘Pink Meidiland’ x R. nitida Defender. The plant bloomed its first season 3 years ago but has not bloomed since. What I’m wondering about is what does blooming the first season signify about the repeat bloom potential of a mature plant and should this turn out to be once blooming, why would it bloom the first season?
I’m assuming it’s a triploid but I was hoping for viable pollen to use for hardiness and disease resistance from Defender and health and floriferous bloom from PM.
I have heard and read in a publication, ‘Inheritance of flower, stem, leaf, and disease traits in three diploid interspecific rose populations’ David Andrew Shupert, that the ratio is 1:8 for recovering everblooming not 1:4 as expected. In my own experience with large crosses of diploids I get 1:8 also.
I have found that with bridging species like what I V Michurin did in the 1920s are very uselful. With diploids I like using Rosa blanda since it crosses with R. rugosa, R. multiflora, polyanthas and Chinas. I was able to get one seedling of Golden Chersonese but it was weak and not hardy in the 1b-2a climate.
I red more of the comments on Rosa blanda. The one that I use is a cross between a Manitoba and a Labrador R. blanda. These plants accept most other diploids but produce few seeds per hip (they are more likely due to being small rather then low fertility). I have F2s that are fertile using polyathas -hardy, small, reblooming but very ugly. Ames 5 is an example of R. blanda crossing with R. multiflora. Mine is very fertile and sets hips easily.
I like R. blanda and species are not clones; each plant breeds differently.
Also to correct the earlier response. It should be a back crossed to the rebloomer is 1:8 not 1:2 as is expected.
