Last week I got one set of twin embryos that had separate Testa(e?) in the same achene. And I planted them without giving it another thought. This week I came across two sets of twins, one with a shared testa(e?) and the other with separate testa but both in the same achene. One of the nice things about this use of calcium nitrate, is that the seed cover separates and slides off so nicely that it is easier to catch such occurrences.
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Aw, cute. It will be interesting to see how these develop.
That is so cool! I agree with Judy, can’t wait to see if the blooms are twins too! I don’t recall ever seeing twins develop in any of mine.
Based on prior ‘twins’, I think they might occur about one per hundred seeds germinated. That probably varies some with varieties, but that is based on modern hybrids I have used. Definitely just a hunch. Two yrs ago I got 5 sets with about 500+ germinations. I haven’t raised any pairs to maturity-one always seems to be runty and gets culled. Last yr I only remember one set (it’s easy to miss them) and they were quite similar and quite awful-got culled early. I do remember a couple of sets where one just failed to grow-got one or two secondary leaves and just sat there and declined. So far, as ‘cute’ as the baby pictures are, it will take a few more attempts before I find a pair that makes it.
THe runty one can be very special and have the same constitution as the egg- haploid. After meiosis, the original cell that has half as many chromosomes goes through three rounds of mitotic divisions to make 8 copies of itself. One divides to 2, 2 to 4, and 4 to 8. One of those is the egg, two are synergids on each side of the egg, two are the polar nuclei in the middle that get fertilized to produce endosperm and the remaining three are at the other end and are called antipodals. Periodically a synergid develops into an embryo and if it is within the same testa as the fertilized egg that is often a good sign that that has occurred. One can recover diploid seedlings from tetraploid parents. Anther culture has not been successful in regenerating haploid roses (ones with half as many chromosomes as the parent) and it has been difficult to get haploids through unfertilized eggs. There is a French group that has done that. Pollen is irradiated and used in pollination. Somehow it encourages some eggs to form into embryos without normal fertilization. THose embryos are saved and put into tissue culture before they abort after a couple or so weeks because of non-functional endosperm.
Having diploid genetics of our modern tetraploid roses can be very useful in bringing those genetics into hybrids with diploid species and cultivated roses and open new opportunities. These first diploids extracted from tetraploids can be very weak and carry a lot of deleterious recessives that are exposed. If we carefully raise these and find those special ones that are fertile and a little more vigorous they can be very good bridges to some interesting breeding directions as well as genetic studies. It is much easier to look at and understand segregation in diploid crosses than tetraploid crosses where there are so many more possible alleles segregating.
My plea is for us to save these runts and view them as treasures to open up new understandings and directions in rose breeding.
Sincerely,
David
I usually mark the twins on their stake. Maybe I need to start flagging them. If they survive the cold nights, and I believe the cold nights are culling devices themselves, I will treat them with a little more respect after hearing your explanation. I would like to see the results of some blooms for comparison, etc. It is so early, I know I will find some more.
Here is a picture of 'Rise ‘N Shine’ and a haploid (diploid plant) from it. The haploid is on the left. The leaves and flowers are both smaller. Unfortunately, this haploid is not fertile. The other two photos are of seedlings from this year each with a twin from the same testa. The smaller seedlings were very very small and took a lot of care for keeping the humidity just right to get them to survive. I plant them in the same pot at first to keep track of which came from the same seed. I’ll count their chromosomes after they are larger and are in their own pot.
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Nice photos, great illustration of your explanation. I am keeping a little better track of the twins-for instance I have Sharpie-black magic markered them, so that they stand out somewhat. And all are doing well so far-the birds did get one of one set, but I still have three complete sets. I really have to transplant (separate) the one set that I could not separate when newly planted-or maybe they are co-joined. One of those has three cotledons, but it is the runty one. The first set is planted in the same pot, and like yours one is definately much different. The second set is quite similar in size and both seem to be growing at a similar rate. Unfortunately I have no sheltered greenhouse space for them to be sequestered in, but am keeping them in an area nearer to the house for now. The sun has been so brilliant (was in the 70’s again yesterday) that I would hate to cook them in a mini-greenhouse.
David Z, a couple of questions if possible, your first photo’s have blue(?) wool tied around some of the spent flower heads, is this for one’s that you have pollinated.
The other part to this question is you seem to have your pots in plastic on a steel tray, do you mind explaining your method. I am gathering all info I can on raising seeds/seedlings, Regards David.
Hi David!
Great questions. I used colored yarn on the Rise 'N Shine plant that year. Most of the time I use paper strung tags to mark crosses that I write on. I dip them in polyurathane and let them dry before I write on the paper so it lasts longer. I had very few pollen parents and the Rise 'N Shine plant in a pot in a sheltered location, so decided to use different colored yarns for different pollen parents. It worked out well. The yard does fade some, but it lasted. George Mander uses colored coated wire which may be easier.
The tray is plastic. I pot up the seedlings (most are in 6 packs) and I keep the humidity high over the top with plastic domes. After a few days I prop up the sides to reduce the humidity slowly. After a couple true leaves are on them they are fine and I eventually take the cover off. With super special roses I pot in those 3" pots and use a baggie to manage the humidity. The seeds are in baggies of moist peat and germinate there before I transplant the out. The humidity transition helps. Sometimes going from the baggies to potting them at ambient humidity leads to the growing point drying out. I like to use Pro Mix with biofungicide to pot seedlings.
Take Care
We also use a 4-inch piece of telephone wire to identify different pollens. We used 39 different colors a couple of years ago, and there were many more to choose from. Used tags for so many years so we could include a date, but when all the crosses are made the last part of June, it really doesn’t matter all that much. I just make a label for the baggie after I harvest the seeds and get them stratifying. There are many different pairs of colors in a large cable, which might have 30 or more pairs. Phone companies used to leave pieces of cable near the junction boxes when they worked, but now with copper prices what they are, they probably keep them. We use the same concept when propagating cuttings. I just keep a master list of colors assigned to a specific rose.
Thanks David for you reply and explanation, I can understand it now. I will save some of that for later experiments.
John, the idea of telephone wire sounds great. I will be out on the weekend looking for any that looks not in use (Ha Ha Ha). I have a freind that works for our phone company and will ask him over the weekend.
Regards David.
Here is a photo of two sets of twins that have survived. Did not note whether they shared a testae or were separate. The birds did scratch and devour/pull out by roots the other sets. One or two did die unassisted. This one just opened today. It is a Gemini x 34-06-05 cross. The ‘runt’ is very fragile looking, is a single, and is a vermillion pink. It looks like the larger one (which is smaller than most of its’ seed batch mates) will be a bicolor, double, possibly red with some orange/pink/ yellow.
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[attachment 674 2012newseedlings020.jpg]Here they are easily compared.
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The lower one is also very small, although the flower is huge. The smaller ‘runty’ twin is very, very small and is maybe two weeks from flowering-just formed a bud in the last day or so. They both seem fairly healthy.
I marked as twins when potting up and will keep a special eye out if they ever break surface of the two seeds from one achene. Neil