I am really excited about finding these twins this morning and thought I’d share it. Hopefully I can get these twins to live. A few years back I had twin seedlings from a seed of R. pomifera. They shared the same testa (papery outer covering). One was a little bit smaller. The smaller one was 3x and the larger one 4x. The 3x one is most likely a synergid that developed into an embryo and in essence is a haploid (same genetic makeup as the egg before it was fertilized). With R. pomifera the egg is 3x and pollen is 1x. So, this 3x seedling grew and matured and it flowers and fruits well. Its seedlings have consistently been 3x as well. It blooms so early there is not anything else around besides R. pomifera to cross with anyways. So, it seems logical that the eggs of it are 2x and pollen 1x. Now there is a set of twins from this 3x R. pomifera!!! Maybe this smaller seedling will be 2x and the larger one 3x.
Perhaps a 2x version of a Caninae section rose would be very useful for genetic studies and understanding the ancestral genomes within this strange section of roses. In essence if this smaller seedling is 2x perhaps just two of the genomes are isolated and useful for especially molecular work. Perhaps it will also be an interesting breeding link to bring fragrant foliage into some modern hybrids. Using pollen of Caninae section roses that is 1x has some limitations because it probably is just a single genome represented and crosses seem more difficult using Caninae section species as males on other roses compared to visa versa, at least for me. On the egg side there are so many genomes represented and the offspring is generally very similar to the female, that it complicates breeding. Perhaps this seedling, if diploid, would offer a unique opportunity to generate modern hybrids with just the genomes it contains.
Last spring I shared 3x R. pomifera seedlings with those interested and hope to be able to do so again this spring.
David, that is great news. I find it interesting that your 3x R.pomifera was from a twin also. It seems to run in the family just like some roses produce a lot of sports. It will be intriguing to see if this smaller plant survives and if it is in fact 2x. If it is 2x with just the univalents from the 3x, it will be interesting to see what characteristics it has and if it is fertile. Keep us up to date on this.
I got the twins home safely, separated and potted up. Master Gardeners help me collect rose seed germination data at work on Tuesdays and seed from this 3x pomifera was included in the experiment. I was helping them count yesterday and found this twin! I had it in a plastic bag all day with some water and was holding my breath as I separated them and potted them up when I got them home. I’m hopeful too Paul if the smaller one is 2x and would have fertility despite its strange combination of genomes that probably are univalents normally. That’s a neat trend of twins from a twin. It sounds like people have selected for it in cotton and over generations increased the rate. If my memory serves me I think they eventually got it to either one in 100 or 1000 seedlings having twins with one as a haploid. The French rose research group working with haploids had a 4x egg of R. canina develop (from normally 5x R. canina) and they found basically no fertility in this 4x plant except I think for 2n eggs where all the chromosomes went together. It’s sure a treat that this 3x pomifera is very fertile. In fact it surprisingly has comparable hip set and seeds per hip as its 4x twin it is planted near. The smaller twin actually has some pretty good size to it and I’m hopeful it will live. Hopefully in a couple months I can sacrifice some root tips and see what ploidy it is and give an update. I was able to get some pictures before potting it up and will try to pass one along to Peter for the newsletter.
The R. pomifera twins are both surviving and making their first true leaves!!! Last night as I was potting up seedlings I found 2 more sets of twins from general tetraploid shrub rose crosses which shared the same testa. From my potato work where haploids from tetraploid potatoes are so important for use in crossing with wild diploid species it was important to generate a lot of haploids. Many were not very fertile or were weak and it took a lot to sort through to find those that would be useful in breeding. It seems that the same holds true for roses from what the French group reports and what I have found with my limited number. Hopefully as we keep our eyes open for haploids we can eventually find some good diploids from tetraploids that would be fertile and useful. I have a yellow haploid (diploid) out of Rise 'N Shine, but unfortunately it does not produce any anthers and has not been female fertile in crosses yet. My haploids out of ‘Dorcas’ grew well for awhile and them fell apart and died. There was one gorgeous one that was stippled and well branched and floriferous- like a diploid China rose. Too bad it died.
Until some good haploids to work at the diploid level come about from modern roses maybe the most productive way to get to the diploid level for those of us who want to would be to cross triploids onto our diploids. Hopefully there will be some diploid offspring that have traits of interest primarily found in roses at higher ploidy levels. I have gotten a diploid from open pollinated ‘Nearly Wild’ seeds and a 3x seedling of mine, although most op seedlings were 3x or 4x.
How many others are finding and working with twins or interested in going to and working at the diploid level?
Robert, I don’t know if you have heard of the found rose Peggy Martin but I just ordered one from Petals from the Past Nursery. It blooms in the Spring and again in the Fall and is suppose to be completely disease resistant and thornless and probably diploid. Here is a story on it.
Interesting! Renae and it’s siblings are also diploid as should be Cl. Pinkie.
I also plan on using a prickle free diploid mini seedling of mine called’Petite Perle D’or’ and another prickle free mini a friend of mine created from R. helenae and R. rouletti called “HelRou”.
I work almost exclusively on the diploid level, but there are some traits that I will need to pull down from tetraploid cultivars.
I had planed to produce triploids in the hope of recovering diploids in the F2. Perhaps it would be worth producing some self pollination’s of those tetraploids in the hope of finding twins and obtaining some haploid seedlings.
Are there any tetraploids that have been noticed to produce more twins than others, particularly yellows, velvet reds, and “blues”?
Hi Jinks, That’s a great question about some more prone to produce twins. ‘Dorcas’ has been one for me. Since most people aren’t looking for those small twins, I think they get overlooked and lost and die from lack of attention when they are especially small. One key I think for what roses can produce them is genetic load. Roses like ‘Dorcas’ seem to produce consistently vigorous seedlings and I think have less deleterious recessives that once unmasked can lead to some weak and more variable fitness. Haploids tend to be relatively weak (of course there are exceptions) and roses with less genetic load and potential for haploid seedlings with less fitness problems should hopefully be more likely to produce those that survive and have fertility. In potatoes the cultivar ‘Atlantic’ has been really good at producing useful haploids. There is also greater or less propensity for producing twins with haploids. In cotton those that tended to produce them were intermated and then some cotton lines were found that produced even higher rates of twins.
You do not need to self your tetraploids to get haploids from twins. The weaker haploid twin tends to be a synergid that has the same constitution as the egg. If you are using tetraploid parents anyways in breeding you can just look for a smaller twin and what the dad of the larger twin is may not matter.
Sometimes an unfertilized egg will develop into an embryo as a haploid. Pollination does generally need to occur to fertilize the central cell so there is endosperm so the embryo can survive. My haploid of Rise 'N Shine came from a cross of RNS x a one time blooming species rose hybrid. This little seedling flowered and it was a clue it did not have the one time bloomer as a dad because the dad should not be segregating for reblooming offspring. The seedling turned out to be diploid. You may choose to pollinate your favorite tetraploids with males you know should produce all one time bloomers and look for the stray rebloomers.
I think the potentially most fruitful approach would probably be to take some modern triploids that have the traits we want (there are more triploids than I suspected from my work) and purposefully bulk pollinate them with diploid pollen and find fertile diploids among the seedlings. Flower Carpet Yellow, many of the warm colored Hybrid musks, Red Meidiland, Starina, Tropicana are triploid. It can be hard to get seeds and viable seedlings from triploid females, but it is possible and after the obstacle is crossed and we get some fertile diploids we can go from there. Some triploids are better than others at female ferility. We can use triploids as males on diploid females and we can get diploids too, but pollen competition would probably favor pollen with higher ploidy based on some of the data from the French group and in other crops like potato. I have some data from tetraploid x triploid crosses where I got triploid offspring pretty readily though.
Hi Jinks, That’s a great question about some more prone to produce twins. ‘Dorcas’ has been one for me. Since most people aren’t looking for those small twins, I think they get overlooked and lost and die from lack of attention when they are especially small. One key I think for what roses can produce them is genetic load. Roses like ‘Dorcas’ seem to produce consistently vigorous seedlings and I think have less deleterious recessives that once unmasked can lead to some weak and more variable fitness. Haploids tend to be relatively weak (of course there are exceptions) and roses with less genetic load and potential for haploid seedlings with less fitness problems should hopefully be more likely to produce those that survive and have fertility. In potatoes the cultivar ‘Atlantic’ has been really good at producing useful haploids. There is also greater or less propensity for producing twins with haploids. In cotton those that tended to produce them were intermated and then some cotton lines were found that produced even higher rates of twins.
You do not need to self your tetraploids to get haploids from twins. The weaker haploid twin tends to be a synergid that has the same constitution as the egg. If you are using tetraploid parents anyways in breeding you can just look for a smaller twin and what the dad of the larger twin is may not matter.
Sometimes an unfertilized egg will develop into an embryo as a haploid. Pollination does generally need to occur to fertilize the central cell so there is endosperm so the embryo can survive. My haploid of Rise 'N Shine came from a cross of RNS x a one time blooming species rose hybrid. This little seedling flowered and it was a clue it did not have the one time bloomer as a dad because the dad should not be segregating for reblooming offspring. The seedling turned out to be diploid. You may choose to pollinate your favorite tetraploids with males you know should produce all one time bloomers and look for the stray rebloomers.
I think the potentially most fruitful approach would probably be to take some modern triploids that have the traits we want (there are more triploids than I suspected from my work) and purposefully bulk pollinate them with diploid pollen and find fertile diploids among the seedlings. Flower Carpet Yellow, many of the warm colored Hybrid musks, Red Meidiland, Starina, Tropicana are triploid. It can be hard to get seeds and viable seedlings from triploid females, but it is possible and after the obstacle is crossed and we get some fertile diploids we can go from there. Some triploids are better than others at female ferility. We can use triploids as males on diploid females and we can get diploids too, but pollen competition would probably favor pollen with higher ploidy based on some of the data from the French group and in other crops like potato. I have some data from tetraploid x triploid crosses where I got triploid offspring pretty readily though.
There are many possible benefits. If the smaller twin is actually of lower ploidy and has the same genetic constitution as the unfertilized egg, you have some differences to work with. You may get less Caninae section contribution when using it as a female in crosses with other roses because of the potential for less Caninae section chromsomes coming through compared to the typical species. Many of us have experienced the only way to get viable hybrids is using the Caninae section species is as the female parent, so this helps. Caninae meiosis can break down more readily in these roses missing a chromosome set. The balance of genomes and dosage is disrupted and some chromosomes that did not pair during meiosis before may be able to now and there is more potential for differences among gametes from the Caninae section gametes. Selfs of my triploid R. pomifera segregate more widely for leaf morphology and plant vigor which may be an indication of this breakdown and potential for new recombination events.
Good luck. Another group that generated 4x R. canina plants from basically unfertilized eggs of 5x versions had a lot of sterility and in the offspring of them used as a female the only gametes appear to be 4x and were 2n. Perhaps if you have a 4x plant your would be different. My 3x R. pomifera definately is fertile and even has similar fertility to its 4x twin.
One of the embryos is only slightly smaller than the other. (say 15% smaller).
They were interlocked in a parallel configuration with the same polarity (root end / cotyledon end). ie. they were like a person giving another person a “piggy back” (as we say here down under) - I hope this translates to something understandable).
They both had a viable pearly-white appearance.
Their line of apposition was clearly visible running midway along the unit in a transverse manner.
When placed in water they did not separate, and there is some possibility they are conjoined.
I planted this “double embryo” immediately, and now await the results. I guess they should be up in a week or two at the most if they are viable.
I have twin embryos that I just extracted from one single testa covering of Rosa Canina.
Good work - canina embryos are among the most difficult to extract intact. I find the seeds to be much like miniature Brazil nuts, having very hard and fibrous pericarps and sutures glued together with epoxy.
I did the extraction with what is known in our neck of the woods as a Stanley knife (maybe you guys know them as box cutters or razor blade knives?).
Anyway, the reason for my “mad pursuit” in R. Canina embryo extraction is that I want to get a few Canina rootstock seedlings going to complement my other rootstocks. No particular reason, just that the plant “presented itself” to me at the right time, loaded with hips.
As I would rather not have to wait up to 2 years or more for the germination by the usual means, I did the extraction method instead…
George… I have a load of rubiginosa seed here that you are welcome to try as well… I’ve found it difficult to strike the cuttings so thought I would try the seeds instead. If you would like some let me know. It’s from the canina complex group of roses, is a pentaploid, and was often used as a rootstock in the past.
Have you ever heard of the Engalls, who grew roses in Sydney? Well Mr Engall (senior), who has since passed away, was the guy that first showed me with his hands how to bud rootstock, bless him. This was about 20 years ago now.
Anyway, he kept going on about “sweet briar” rootstock. Maybe he was referring to the R.Rubiginosa you are referring to here.
I guess if some of these species roses are such a pain to strike, nurserymen are just going to select the easiest rootstocks to root, like good old Multiflora, rather than necessarily anything that may be more suited to local conditions.