'Mutabilis' - has anyone noticed this?

Here in NW Tasmania (U.S. Zone 9b), my ‘Mutabilis’ is evergreen, puts out new growth, and flowers, all year round. One thing I noticed with mine was that none of the flowers produced during the hottest and dryest times of the year set OP hips, but over winter (we get the bulk of our rain during winter and the ground is always very wet), EVERY flower has set an OP hip (whilst everything else around it is leafless and dormant… so they must be selfed). They are not large hips but they are very definately swelling and will probably be ready to harvest in mid spring.

Hey Simon. How old is the plant?

2 years in the ground here George. Only small, around 50cm tall so far (it grows all year round… albeit slowly…).

Mine does this every year.


Many roses, not just ‘Mutabilis’, will not set hips when Summer heat sets in. Most fail to set seed when daytime temps rise above 90F here, in fact.


Most of our days in summer are around 78F (26ish C) with a handfull getting up to 107F (42ish C). I just found it strange that my night time temps are down to 24-25F (-4ish C) to about 54F (12ish C) during the day and it is setting hips when it wouldn’t in spring - autumn when conditions were far more suitable.

Also Simon, maybe the plant has only just started to trigger into fruit production in its lifespan…perhaps it had been a little slow to establish?

Now that spring is approaching , you might find that it starts to set fruit spring summer and autumn. It will be interesting to know anyway…

Many roses, not just ‘Mutabilis’, will set self pollinated hips when Summer heat sets out that eventually do not set spring op hips with or without pollinator help.

In my observation they are mostly either rather self sterile and/or with reduced fertility i.e. triploids. That they are self pollinated is quite reliable here.

This is also the second year it has done it.

Roses have a self incompatibility mechanism and the form that it has is a gametophytic system rather than a sporophytic system. Diploid roses tend to express SI more than diploids, even though if we get down to it our polyploids likely express it in some ways as well. With a gametopytic system the pollen germinates and the tube gets stalled out within the style from pollen grains of self pollination or pollen that has the same particular alleles for the S gene from a different parent. There are proteins in the style that interact with the pollen tubes. Those pollen grains from different parents (with different S alleles) do not get stalled in the style and have the advantage of getting to the ovules at all or faster and participate in fertilization.

Heat can denature proteins and make them less effective at their job and allow pollen tubes from self pollen to grow through and participate in fertilization. I have had this happen in the greenhouse in summer with many diploid normally self incompatible polyanthas. I raised seedlings from those hips and am convinced they are selfs due to particular traits. For instance, thornless stems are recessive in this germplasm and the seedlngs from the one thornless rose I had in the greenhouse were all thornless even though there were thorny roses all around it. Flower color and double versus single blooms were all consistent with self fertilization as well.

The gametopytic SI system is more leaky and easier to work around than the sporophytic system and thankfully roses are have the one we can work around if for our objectives we would want to.



Diploid roses tend to express SI more than diploids

I mean more than tetraploids.

If such mutabilis selfs are then germinated, what good or bad characteristics could they bring into breeding… (eg. inbreeding problems, or fertility issues, or better genetic mix through meiosis gene shuffling etc…)

That’s a great question George. Inbreeding can theoretically be helpful to get rid of alleles that contribute to weak growth or traits we don’t want. Rose breeders have not really pursued parent building that much it seems using inbreeding, although theoretically it should be possible. Perhaps on a grand scheme of things we kind of do as we use common parents over and over and over generations many modern roses trace back to common parents (i.e. Charlotte Armstrong, Peace, etc.). Peter Asher at the U of MN really challenged the typical mindset of breeders of clonally propagated crops with his work with mums. Mums are hexaploid and typically breeders keep crossing divergent parents in order to try to avoid some inbreeding depression and get very heterozygous offspring. This works to a large extent, but after time goes by it seems like the overall quality of the progeny goes down and we need to raise more and more seedlings to get the better ones because maybe we accumulate and mask deleterious alleles and they begin to express themselves as we reshuffle more and more related lines as the years go by it seems. Peter used inbreeding as a genetic seive to get rid of someof these deleterious alleles. He went ahead with inbreeding and experienced some depression. He saved the most vigorous of the inbred offspring and then these became much better parents in future crosses with many proving to transmit a higher percent of selected characteristics like flower color and vigor and other things. Later on in the populations he raised from which to select his advanced selections he was able to find a higher rate of what he was looking for. He compared the old practice of crossing the most unrelated plants we happened to have anymore as a remnant mindset taken from dog and other animal breeding. He said many had a crazy idea in their mind of one in ten thousuand or whatever it happened to be would be good enough to be a cultivar. He said he would prefer to breed smarter and not harder and although there is chance in plant breeding he didn’t want to just play pollen roulette. I really enjoyed the conversations we had and he really got me thinking about a lot of breeding practices.

Even though we aren’t likely to be able to inbreed enough to develop parents for F1 seed hybrids that come uniform from seed like petunias, we can use the principles they use which includes inbreeding for parent building in our rose parental lines from which we select our clonally propagated cultivars.

THere is slso the idea proposed and demonstrated by an alfalfa breeder at Madison of getting through the valley of death. In alfalfa the first couple to few generations of inbreeding resulted in very weak seedlings and high inbreeding depression. After a point, working with that germplasm and most vigorous individuals for continued inbreeding resulted in improved offspring even without wide outcrossing. One would begin to work out of this valley of death and back up the other side.

I suspect roses like Dorcas and some others that tend to produce relatively consistently heafty and vigorous offspring compared to other roses with a wider array of vigor may have less deleterious alleles (likely mostly he deleterious alleles are recessive).

I think raising your self seedlings of Mutabilis may result in finding some that accumulate the more favorable alleles you would like to get from Mutablis and pass on to offspring and yet have enough fertility to do so.

I should do more work in pursuing trying Peter’s ideas that he demonstrated so well in mums with roses!!!

Thanks for the excellent reply David :slight_smile:

You said:

“Heat can denature proteins and make them less effective at their job and allow pollen tubes from self pollen to grow through and participate in fertilization.”

If the proteins are in place as a selfing barrier and the warm weather denatures them, would I not expect to see more selfs during the warmer weather instead of newly formed flowers during the winter months?

Hi Simon!!

Yes, that is true!!! I think I misread your post! The denaturing and temperature thing overcoming SI is true with many self incompatible roses. With winter and your cooler temps this like you suggest is unlikely the cause in your case. Some roses generally have a more leaky SI system too compared to others beyond the plasicity that comes into effect based on temp. and maybe that is part of it.

Maybe your key issue with no seed set during the summer is the moisture aspect. How hot is hot for you? In the greenhouses where I got selfing from normally SI diploids it would get up to 100F or so during the day. They were well watered and the humidity was relatively high as well I suspect.


David, is it possible to check for the presence of the S allele?

Also, you raise a very interesting point about inbreeding. My feeling is that rose hybridizers have accomplished results in a similar way to Peter Asher, albeit inadvertantly. Generally speaking, to the extent that they can be quantified the lineages of modern roses are essentially a series of introgressions (about 21 generations long) concentrating the genes of R. chinensis, R. moschata and the foetidas with lesser contributions from R. multiflora, R. roxburghii and R. wichuraiana (in that order, btw).

Hi Don,

That’s a great question about testing for the presence of the S allele. I don’t think we have the tools readily handy in roses to do a good job at that. For instance, in cherries I believe and maybe in apples different S alleles have been numbered and cultivars characterized. It is so important for those crops because it influences which cultivars to put together in an orchard for cross pollination and good fruit set. In order to characterize S alleles and begin seeing how many different ones there are there needs to be series of crosses made and understanding of which combinations work and don’t work to build the matrix of data to assign numbered alleles to different clones.

One interesting thing that is in the literature and suggested, is that often at the diploid level we have SI expressed in crops, but at the tetraploid level it breaks down and selfing is more common. This is true with the polyantha roses I doubled as well as common in modern potatoes too. The idea is that the diploid may be S1S2 and then the induced tetraploid S1S1S2S2. SI is still active to some degree. Gametes that are S1S1 or S2S2 supposedly stall out in the style, but only those that are S1S2 get through. Somehow having this heterozygosity in the gamete even if it is the same alleles found in the maternal tissue can allow those gametes to go through. The induced 4x polyanthas set hips routinely in the greenhouse when the temp was moderate and the diploid polyanthas couldn’t it seemed due to SI.

Thanks for your thoughts on the different species and ordering them. It is sure interesting to think about!!

Simon, it’s also possible that the hips are seedless. If this is the case then there has been no self-fertilisation, just parthenocarpy.

Putting it in another way, I am wondering whether these odd hips have empty achenes which would suggest no fertilisation has occured… just a thought that’s all…

The hottest day last year was up around 42 degrees Celcius (about 107F). It doesn’t often get that warm here and average is about 26 degrees celcius (78ishF). So it is pretty mild really and the soil here is almost always moist (and under a thick layer of mulch). The hips have seeds developing in them (as mentioned above, I have some from the previous season that have just come out of the fridge on Sunday) though I haven’t checked inside them for an embryo as there weren’t enough for me to sacrifice, even to try some embryonic germination (not good at it yet… it quite literally leaves me feeling a little… crushed LOL). I should also mention that I have not tried deliberate crossings at any time on it either.