Unreduced pollen in roses

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david zlesak
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Unreduced pollen in roses

Post: # 69648Post david zlesak
Sat Apr 06, 2019 10:25 pm

There is a new article studying unreduced/2n gametes in roses. Below is the link. I feel the authors did a great job studying this topic. There are some typos, lack of capitalization of rose cultivars, etc. In some of these open access journals there is often less quality control. They cited my 2009 paper and misinterpreted the data I presented on alba roses. "In R. alba hybrids, 2n pollen was produced and
abnormal ploidy was observed [14] ". They are mixing up n and x. n refers to life stage. 2n means the sporophyte stage (typical plant cells in leaves stems and roots). The gametophytic stage is 1n or n. These are the gametes or gametophytic stage. When there is a gamete (like pollen or an egg) that has the same chromosome number as the parent plant and the gamete did not go through the full standard meiosis leading to typically half the chromosome number, we can say it is 2n pollen- pollen with the same chromosome number as the plant (sporophyte) that generated it. Anyways, their photos and data seem reasonable and sound and I really love what they did. I was hoping someone would answer some of these questions in roses and was really glad to see this article.

It is interesting that in the cross they made they found that although the percent of 2n/unreduced pollen in 'Old Blush' is low (1.39% in their samples), after they put the pollen on 'Orange Fire' the stigmas allowed a greater percent of 2n pollen into the style than normal n pollen and the seedlings they obtained then had a higher than 1.39% rate of tetraploids. 'Orange Fire' is tetraploid and 'Old Blush' is diploid. The normal n pollen from 'Old Blush would lead to triploid seedlings and 2n pollen tetraploid seedlings. It would be great if they would have also used the 'Old Blush' pollen on a diploid mom to see if the stigma of the diploid also preferentially let the 2n pollen through. I think from some of the papers by some of the French rose researchers years back, that there were some clues that maybe there was some degree of preference. n pollen tended to fertilize diploid moms to a slightly greater extent and 2n pollen from diploids fertilized tetraploid moms to a slightly greater extent.

https://bmcplantbiol.biomedcentral.com/ ... 019-1696-z

I was transplanting polyantha rose seedlings tonight and it is fun to very rarely see some that look like they may be polyploid. The two pictured are open pollinated (likely polyploid on left and diploid on right). Perhaps the one that looks polyploid is a hybrid with a triploid or tetraploid rose, or maybe it is a hybrid with other polyantha and there was some rare 2n pollen grains in that polyantha dad. The typical polyploid characteristics include-wider leaflets that overlap each other more, thicker leaves and stems, and less branching. I'll check its pollen size and maybe do a root tip squash to double check its ploidy. It'll be great if it is tetraploid instead of triploid and fertile. I'd love to cross it with standard tetraploid shrubs and hopefully more readily generate hybrids with a good amount of fertility to move forward with.
Attachments
tetraploid and diploid polyantha rose seedlings.jpeg
likely polyploid on left and diploid on right

philip_la
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Re: Unreduced pollen in roses

Post: # 69650Post philip_la
Sat Apr 06, 2019 11:23 pm

A little off-topic, David, but in the case of unreduced pollen from a diploid creating a polyploid, are those polyploids likely to have any more cold-hardiness than their diploid seedlings? I recall reading that polyploid species are more common in colder climates, but don't recall the supposed reasons for such. It might have had more to do with insuring a greater diversity in offspring in a harsher climate than a correlation with hardiness per se.
Philip F.
[size=small][color=#669966]Zone 8 / Sunset Zn 30 (Austin, TX -- formerly New Orleans, LA)[/color][/size]

jbergeson
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Re: Unreduced pollen in roses

Post: # 69653Post jbergeson
Sun Apr 07, 2019 9:21 am

Thanks for this post, David.

Do you have any thoughts on cross direction in regards to combining polyanthas with modern tetraploids? Pollinating polys is a painstaking process, and I don't seem to have the knack for germinating them, so I'm inclined to use their pollen. (also thinking of Darlow's Enigma, which I don't know if qualifies as a poly but should function the same). I've used Candy Oh! as a pollen parent as well as Darlow's Enigma. In both cases it's a little hard to verify hybridity of the seedlings, as the seed parent's characteristics will somewhat dominate. But I've gotten seedlings that I'm pretty sure are successful crosses. Would you speculate that polys would have a similar rate of unreduced pollen as Old Blush did in the study? In that case, using polyantha pollen on modern tetraploids or triploids would have a better chance of creating a tetraploid that is 50% poly.

david zlesak
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Re: Unreduced pollen in roses

Post: # 69654Post david zlesak
Sun Apr 07, 2019 10:42 am

Those are great questions. It seems like with polyploid series like you mentioned Philip that the higher ploidy is found in the more harsh/severe end of the range. What I've heard is that polyploid allows for more alleles to be housed within the plant from which to hopefully accumulate alleles that contribute to adaptation/survival. That is an interesting thought. Polyploids in general (there are exceptions) seem to grow a bit slower. I had a 8x R. acicularis that was really slow and thick in growth. Perhaps they harden off better come winter too and tend not to push as hard into fall? I'm not sure.

That's a great question Joe :0). I agree it would be really fun to get more hybrids with polys and a range of polyploid modern roses. It has been very hard, at least for me, to bridge polys and typical fertile modern roses like Carefree BeautyTM and others. I've tried both directions and haven't gotten much success. There is one hybrid I still have in a pot from after the move and need to get propagated that is a poly x 'Champlain'. It is a nice deep pink with a very nice plant habit. It is from 1999. There were some hybrids with it I liked years ago, but lost them in the moves. I wish it was healthier. What seems to really work is polys- diploid or tetraploid- with fertile tetraploid minis. 'Hannah Ruby' is a triploid hybrid with a diploid poly and 'Honeybee' is a tetraploid hybrid with an induced tetraploid poly. I suspect what is allowing those hybrids to work so freely is that the Moore minis I've used in the past ('Rise 'N Shine', etc.) have some polyantha-like parents in the background and bring in a good dose of Systylae genetics (R. multiflora, R. wichurana, etc.) to match or work well with the same species backgrounds in the polys. I haven't kept up on the new minis. Maybe there are some healthier/hardier ones that could be a good bridge now. I like what you mentioned about using some triploid modern roses too. 'Golden Angel' is triploid and seems to be a nice bridge between ploidy levels. It is a parent of the diploid 'Topaz Jewel' (other parent a rugosa). Knowing it was the parent of a yellow diploid hybrid is what got me interested in wanting to use it to cross with polys to bring in yellow and stay at the diploid level. Years back I got a plant of GA and put poly pollen on it and got several hybrids. I counted some of them and those I counted were diploid. They were pastel and some had a bit more modern form to the blooms. Unfortunately, they weren't fertile and I lost them over time with harsh winters. Last year I bought some more GA's from Burling hoping to try again with some of the current polys I have around. I think it's possible to find some good polyploid modern roses with the right background to accept poly pollen and make the crossing easier. It'd be great to learn others suggestions for which roses may be good to try.

Karl K
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Re: Unreduced pollen in roses

Post: # 69663Post Karl K
Mon Apr 08, 2019 2:38 pm

philip_la wrote:
Sat Apr 06, 2019 11:23 pm
A little off-topic, David, but in the case of unreduced pollen from a diploid creating a polyploid, are those polyploids likely to have any more cold-hardiness than their diploid seedlings? I recall reading that polyploid species are more common in colder climates, but don't recall the supposed reasons for such. It might have had more to do with insuring a greater diversity in offspring in a harsher climate than a correlation with hardiness per se.
Simple answer, Not necessarily.
Fagerlind (1958)
k. Rosa multiflora—tetraploids from diploids—three individuals, badly frozen each year. Earlier, one of them flowered rather richly, but not at all in recent years. All these specimens are now languishing considerably.
http://bulbnrose.x10.mx/Roses/breeding/Fagerlind.html

Fagerlind lived and worked in Sweden, near the northern limit of this species. Doubling the chromosomes just pushed them over the edge.

On the other hand, I've read that 'Hansa' grows happily and flowers freely in Alaska.

People who still believe that Rosa acicularis is a "pure" polyploid series including diploid, tetraploid, hexaploid and octoploid varieties are beyond saving. Those who are capable of considering more than a handful of traits at a time (e.g., Hurst) can see that the polyploids combine traits of more than a single ancestral species. It is the combination of traits that allow some polyploids to survive in the far north, but not because they are thrown together.

Hurst (1925)
In the most complex case studied, in the octoploid species BBCCDDEE (R. acicularis Lindl.), the four double septets seem to work more or less in relays in different parts of the plant at different times and seasons, resulting in a periodic predominance of one septet over another in certain parts of the plant, the general result being more or less a mosaic of the four septets of characters arranged end to end or side by side.

Naturally with four double septets working equally and independently in an octoploid species, only about one-fourth of the characters of each septet can be represented at one time. An analysis shows that in a plant of R. acicularis Lindl. carrying four years' growth of surculi, stems, branches and branchlets, about one-half of the characters of each of the four septets B, C, D and E were represented (fig. 174 e and f).
http://bulbnrose.x10.mx/Roses/Hurst/HURST2.HTM

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