Still trying to wrap my head around Canninae meiosis, and how to overcome...

In prior discussions, the notion of overcoming the Caninae Meiosis of e.g. Rosa glauca (as a mother, to maintain desireable qualities) was likened to trying to steer a large ship with an oar while the rudder was in a set position. I presume this is primarily a question of quantities of genes, but perhaps also their willingness (or lack thereof) to segregate in a manner that stops the canninae tendancy, while maintaining a preponderance of the good qualities. Poorly worded, I know, but I mean to ask, do daughters segregate the same as their mothers and always keep the same sets of non-paired genes?

Several years ago, I said that if I lived in a more amenable climate and could access the plants, I would love to cross glauca with a hexaploid (e.g. Rosa sweginzowii) to see if that shot of genes could integrate and break the mieotic connundrum.

Just curious if any of you more educated minds have any idea how such a hypothetical might pan out?

That’s a great question Philip. Here are some thoughts that come to my mind. In the past, I found a 3x R. pomifera (it is tetraploid and in the Caninae sections). There were twins from a seed- larger was typical 4x and smaller 3x. The seed was a suspected self as R. pomifera is the first to bloom and there was nothing else in bloom. The smaller 3x twin was likely from a cell called a synergid, which has the same genetic makeup as the egg. With Caninae meiosis, the eggs of the parent would be 3x and pollen 1x. This triploid was/is fully fertile with well filled pollen that is the typical diameter for 1x pollen. Selfed seedlings of it are also 3x, suggesting eggs are 2x. The two sets of chromosomes that seem to traditionally pair during meiosis in Caninae section roses were disrupted in the 3x R. pomifera because one of them was lost as it was not fertilized by typical 1x pollen. Another set of chromosomes in the triploid seems to be working to pair with a complement set to restore the Caninae meiosis. The triploid selves seem to have a bit more visual variation. Perhaps this is due the pairing and segregation of some chromosome sets that have not been pairing before and just transmitted wholely as is through the eggs.

I have some hybrids of R. pomifera x polyanthas. The hybrids are 4x and have the size of 1x pollen, so the specific sets of chromosomes that are pairing here too seem to be altered. Likely two sets of R. pomifera chromosomes are pairing during meiosis.

I have a 6x hybrid of a 5x R. eglanteria x a typical tetraploid modern rose. Pollen is fertile and the size expected for 2x. It seems like the 4 sets of chromosomes that got passed along from R. eglanteria reestablished the Caninae meiosis with two of those sets pairing well. I assume then the 2 sets of modern rose chromosomes are likely pairing between themselves. The 2x pollen is likely one set of modern rose chromosomes and one set of R. eglanteria chromosomes. This sort of pairing seems to be happening in hexaploid Alba roses too (2x pollen). Albas seem to be a hybrid of some 5x Caninae section species and the tetraploid R. gallica.

So, to try to answer your question, it seems like in hybrids with other rose groups, the Caninae section meiosis seems to often continue when the Caninae species is the female, although in a somewhat slightly altered way.

It has been very hard to obtain hybrids of for me of Caninae section species used as males on modern or other sections of rose species. Once in awhile when there is a seedling that direction, it is very weak.

The Caninae species and their hybrids demonstrate two important aspects of heredity:

  1. Genetic regulation of chromosome pairing
  2. Segregation distortion (all the unpaired chromosomes present in the ova, but none in the pollen)

In a diploid Rosa species with 14 chromosomes, we expect these to arrange themselves as seven pairs for meiosis. But what happens when we are dealing with a tetraploid that has been assembled from two diploids? [Basye’s probable amplhdiploid is probably an example; R. x kordesii is not.)

How do chromosomes from the two parental species avoid pairing off with the “wrong” partners? If they did, meiosis could become a jumble of pairs, trios, quartets and soloists. This is not good fertility.

In order to reduce chromosome pairing frequency enough to allow fertility, various genes come to the rescue. I have no idea how they accomplish the task, but they do. See Riley (1958), who located a few chromosomes that carried genes that determined whether haploids from hexaploid bread wheat would would behave as a triploid (x=7), or as a monoploid with 21 chromosomes.

Temperature also plays a role. Wulff (1959) discussed the odd case of the triploid ‘Schneeschirm’. During its autumn bloom, this variety was sterile. However, during its summer flowering, “Their reduction division is characterized by the occurrence of only 0-3 trivalents, with pairing to 7 bivalents and 7 univalents or 1 trivalent, 6 bivalents and 6 univalents. This reduction division proceeds rather regularly. The univalents, splitting twice, are mostly taken up into the young tetrad nuclei. Chromosome elimination is low, and so viable pollen grains and egg cells will contain 14 chromosomes.”

That is to say, during the summer this variety acts like a tetraploid, so far as can be seen from its gametes.

And so, when a Caninae species is pollinated by a “regular” species (one that doesn’t do the Caninae mciosis), the mechanism regulating the special system is diluted. Blackhurst (1949) showed what happened in the F1 offspring from R. rubiginosa pollinated by various other species.

Blackhurst’s results look like a hopeless mess, but never fear. Heslop-Harrison (1954) gave examples of Caninae x regular hybrids that were at least partially fertile.

Professor Heslop Harrison emphasized that the F1 lots, whilst conforming, in a general sort of way, cytologically to the usual Caninae pattern, in their later meiotic stages on the female side showed important anomalies. As a result, amongst the seedlings, orthoploid plants were secured carrying chromosome complements of 14, 28, 35 and 42. Thus it was clear that a new polyploid series had been evolved by a distinctly novel mechanism. Further, amongst the seedlings there were encountered aneuploid plants with chromosome numbers 2n=24, 2n=32 and so on.

Apparently, in development a fairly heavy mortality rate takes place, leaving F2 plants, as far as present results indicate, possessing, like > R. spinosissima> , a balanced set of 28 chromosomes. These plants display a regular heterotype division like > R. spinosissima > and a normal homotype division, and are quite fertile. Further, this same fertility is manifested in the F3 and F4 generations. Incidentally, the lecturer pointed out that pinkness in all these crosses is dominant.

I must note that though some of these plants displayed a meiosis like that of R. spinosissima, they were not that species.

About that caninae meiosis as observed with R. pomifera. Some years back I got a seedling for that triploid R pom from David Z. Looks like about 10 yr ago as I had a plant big enough to pollinate in 2010. Crosses have worked apparently both ways but I’m always suspicious of R pom as female parent whether it is a self or out-crossing. The foliage characteristics of R pom are fairly dominant. I have put its pollen onto a range of plants and they come out with foliage like R pom. Successful fertilization is low, germination of the seeds is low. I am working only with tetraploid parents.

Internode length is the one character that seems to vary clearly. A mini mother gave dwarf seedling. Its OP offspring are very dwf. Soeur therese pollen in Rpom gave very tall plant which has not bloomed so far 3 years. Disease suceptibility (BS) is the other trait that can be introduced to crosses onto R pom. It doens’t seem to have dominant resistance to my strian(s) of BS. Germination is generally not very good in a year-long test and most seedlings are abandoned because they lose tehir leaves or look so much like R pom that the odds seem against having anything of interest come of it.

I guess, being a bit lazy, I am putting my main efforts into things like Above and Beyond, and hybrids where I have some advantage.

If I had time and space and access, I’d plant every seed I could collect from ‘Lady Penzance’. A fertile tetraploid with sweet briar foliage would be a real triumph.

On the other hand, I’ve been reviewing some info on the dwarf bearded irises. At one time it was thought (by people who bothered to think such things) that Iris pumila was merely a tetraploid version of I. attica. Subsequent investigation, particularly of chromosome morphology, made it clear that I. pumila is descended from an ancient hybrid of I. attica and I. pseudo-pumila.

This makes a nice story, but one little fact remains: no selections of the putative parents have been found with the (almost) sky blue pigment displayed by some forms of I. pumila.

Maybe the desired pigment requires genes from both the ancestral genomes.

I’m working on it, around 200 Lord Penzance seedlings at the moment, almost a year old, a few flowered around 8 months old, dull yellow with pale pink overlay, not particularly exciting. Also have more seeds from Lord and Lady Penzance to be planted out in a few weeks. Also a few dozen feral sweat briar seedlings (I wanted briars without recent foetida influence just to compare traits/health)…the smell from the many seedlings all nearby each other is very obvious the closer you get to them.

A fertile tetraploid with sweet briar foliage would be a real triumph.

I had the same thought about the pine scented R. glutinosa to which end I made a bunch of crosses with mosses. From these only the crosses with Mosseau du Japon in which glutinosa was female yielded hybrids of which I have four. They all have quite strongly scented pine scented foliage although they are not mossed.

The influence of the canina is overwhelming morphologically although, while glutinosa itself is a very small plant, these seedlings are mastifs like papa. I have not carried them forward successfully despite having made a lot of crosses with their pollen in a hope to break the canina influence. I’m downsizing my stable this year but plan to keep one of these because, well, pine scented foliage.

This seedling is a cross of Alba-semi plena X r. acicularis…and it’s passing the test of time for Zone 2 (USDA) hardiness. It produces hips without seeds to this point…has the foliage phenotype of r. acicularis…and is starting to sucker after approximately five years in a test bed. It’s surprisingly disease resistant but a slow and steady grower…still working with it’s pollen.
ASP X R.acicularis.JPG

Sorry to be slow at acknowledging replies. It’s been a while since I’ve had biology, which combined with my precocious senility makes this all a little hard for me to process. I had to look up Meiosis in Wikipedia so that I can attempt to ask intelligent questions. But just to make sure I’m understanding the process:
Typically, the cells contain pairs of homologous chromosomes, including those from which gametes arise via meiosis.

Meiosis begins with DNA REPLICATION (S-phase) creating identical sister chromatids, which remain held together. (These, I suppose, resemble the X-shaped chromosomes of mitotic division S-phase.)

GENETIC RECOMBINATION (meiotic prophase) permits exchange of genetic info – that which ultimately permits unique gametes (crossovers, etc.). My impression is that these “crossovers” occur strictly between homologous chromosomes, which is relevant to my question below.

SEGREGATION (in Meosis I) results in two, what I think can be called “haploid” cells (containing half the number of chromosomes as the parent cell, technically speaking, though still containing linked sister chromatids – i.e. copies linked to original – which however are not identical due to recombination.)

CHROMATID RELEASE (meosis II) creates another segregation as the sister chromatids seperate and each form a gamete – hence, one cell has ultimately given rise to four unique gametes…

In Caninae meiosis, I presume some of the gametes remain with the egg, as homologous pairs. I presume these are generally the same homologous chromosomes every time, and it seems to me quite probable that the genes controlling Caninae meiosis are contained within these chromsomes, remaining with the egg? This would, it seems to me, imply that cracking the meiosis with the usual 1n pollen isn’t likely to achieve anything.
Hence the reason I was wondering if, in the example I was proposing, there was any possibility of e.g. 3n pollen (from a hexaploid) pairing with, and breaking up, the homologous chromosomes in a (3n) egg (of e.g. R. glauca), thereby ultimately permitting a breakdown of the system. Or is more likely that the chromosomes from the pollen will be unable to properly pair at all, and the cross will simply fail? It’s probably not appropriate to think that random chromosomes from an unrelated species can pair with those of a canninae, but then again, I suppose we do this with every wide cross we ever attempt.

I am making an awful lot of uneducated presumptions here… Would like to hear from those with more knowledge than I (which includes, probably, pretty much everybody! I just act like I know what I’m talking about!)

When I was first learning about the odd Caninae meiosis, I was unaware of two facts.
(1) There is more than one way for a cell to divide. In meridional cleavage, the plane of division passes through the poles of the cell. The resulting daughter cells are about as close to identical as we’re likely to find in living beings. In equatorial cleavage, to the contrary, the cell divides along the equator. The daughter cells are far from identical because …
(2) the cell contains a cytoplasmic gradient. The top of the cell (just to have a point of reference) is different from the bottom because of different substances and concentrations.

In meiosis, equatorial cleavage serves to concentrate the cytoplasmic goodies in the bottom cell of the tetrad, while leaving the top cell with little.

Paired chromosomes are aligned with the plane of cleavage. One member of each pair goes to the lower daughter cell, and one goes to the upper. But the unpaired chromosomes in the Caninae roses always lie just below the plane of cleavage, eventually ending up in the bottom stuffed cell.

In the female meiosis, the bottom cell, with all the unpaired chromosomes, is the ovum. In male meiosis the deprived cell (without unpaired chromosmes, is the pollen cell.

Darlington (1949) gives more information on the cytoplasmic gradient.

Jiang and Gill (1998) discuss a similar case of irregular meiosis involving wheat with a single chromosome borrowed from slender wheatgrass. In that case, the unpaired chromosome found its way into 97% of pollen grains, but only 20% of ova.

Finally, Ann P. Wylie (1975) discusses the case of ‘Carmenetta’, a R. rubrifolia hybrid, that proved to be temperature sensitive in regards to its meiosis.

Probably not the best case scenario given giant holes in lineage but Goldbusch is an example of the canine meiosis having broken down. Its capable of passing on the briar foilage scent (reportedly not as strong) which it had to have inherited via pollen even though the trait is locked in with seed at species level.

While we don’t know what Lucy Ashton is exactly, based on Lord Penzances other breeding and time some guess work probably leaves us with it being a very near (if not first gen) hybrid of rubiginosa. If we assume it’s child Magnifica is an open pollinated seedling we can see that the meisosis was behaving differently from that point forward as Magnifica had to pass the traits via pollen that eventually showed themselfs further down stream. Which leaves us possibly at two non canina out crosses. Granted a number of guesses/assumptions but possibly indicates it may not be the hardest thing to over come.

Doug, I missed your post earlier, and I’m only just wrapping my head around it…

That is, in theory, a hexaploid (huh??!!) (gallica (56n) x cannina (35n)), with a darned-if-we-knowploid (14, 28, 42, or 56n) acicularis? How do Alba Maxima and its sport, Alba Semi-plena, usually segregate when used for breeding? (And how is it hexaploid? Is my math messed up, or shouldn’t it be something else, like triploid?)

That’s a pleasant looking plant in your picture. Do you have any clue as to its ploidy? It’s preferred meiosis?

A hexaploid form of acicularis (or any pollen from such that acts accordingly) might be another interesting prospective mate for e.g. glauca, I think. For that matter, I wonder what alba might do mated with such…