It is really fun to find twin rose seedlings. When there are two that share the same outer coating (testa) and there is a larger and a smaller one, the smaller one is usually haploid I’ve found (having half as many chromosomes as the mother plant). Before fertilization, within the female tissue there are 8 copies generated of the nucleus that is the product of meiosis (sex cell development). One gets packaged in the egg and if fertilized becomes the embryo. The other copies serve different functions. On each side of the egg there is a small cell (synergid) and each gets one of these haploid nuclei. The purpose of these small cells is a bit unclear. Some suggest they serve to filter out viruses that may be coming with the pollen before the male nucleus enters the egg to help protect the new seedling from infection. Sometimes synergids are triggered to start dividing and generate an embryo without fertilization. There is the standard large embryo from fertilization and then a small embryo nestled close coming from a synergid. Some roses seem to produce these sorts of twins more readily than others. The small embryos are often weak and don’t make it naturally. Since I pot up my germinating rose seedlings out of baggies, I can spot them sometimes and baby them along and get some to survive. Often I find them in seeds of tetraploid parents and the smaller embryo is then diploid. Yesterday I found a set of twins in some op seed I raised of a healthy tetraploid yellow rose and got some nice photos. Hopefully this small twin survives and is diploid and has some fertility. It would be fun to cross it with diploid polyanthas and other diploids to bring yellow in. Have others been on the lookout for these sorts of twins? Twins that each have their own testa or covering tend to be the standard ploidy from my experience. There is a single yellow High Voltage diploid seedling from a couple years back I hope to use in breeding this summer that seems to set op hips and have some fertility from being able to germinate some of those seeds. There are a few diploids out of ‘Gaye Hammond’ I need to screen to hopefully find some with a bit of fertility. There wasn’t any op hips on any of them last summer.
That is so cool David. I hope the smaller twin survives and has some fertility.
Hi David
I keep a keen eye out for twins when planting my seeds. I did find two sets last year but as you say the weak one seldom survives and mine have been determined to pass to the other side as quickly as possible. Good luck with yours. All the best. Mike
Old thread, but I thought this was an appropriate place to note that I received my first set of twins this week. In this case, the cross is Papa Meilland x Candy Apple (tetraploid x probably tetraploid), and the two seem to be of equal vigor thus far.
They are beautiful Lee! It’ll be interesting to learn how they develop and if they look alike and may be identical twins or if they look very different. Years ago I had one set of twins that were similar sized out of the same testa and both looked alike for color and stippling, etc. The cross led to lots of variation in the population, so being so similar seems like they may have been identical twins.