Some ploidy questions

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Re: Some ploidy questions

Post: # 69139Post roseseek
Sun Jan 27, 2019 3:46 pm

Karl's final paragraph above may well explain the observed sterility of the early Teas, which led to the presumption that triploids are all sterile. Thankfully, they are NOT!
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Re: Some ploidy questions

Post: # 69144Post jbergeson
Mon Jan 28, 2019 3:42 pm

I'm replying to the original post and haven't read all the responses yet, as I'm too eager to get started procrastinating.

They talk about R. acicularis as having different ploidy levels. I got a bundle of them from Lawyer Nurseries, and they really seem diploid to me...small leaves and stems. The Robert Erskine rose "Aurora", which is supposedly a selection of native R. acicularis, has much larger foliage than the seedlings I got from Lawyer. If the ID's are correct, that might indicate a difference within a species, based upon ploidy.

I really, really want to bring the combination of full hardiness and remontancy of rugosa roses into breeding with modern garden roses. I've gotten some pretty interesting results crossing rugosas with moderns, but the seedlings are usually sterile. For instance, I have a very nice reblooming seedling that is Henry Hudson x Above & Beyond. It is white...if it were bright pink it might be a releasable rose for northern climates. (and if it was any shade of yellow or orange it would be a bombshell). Anyways, I've had fantasies about in vitro chromosome doubling to create a hexaploid, the pollen of which could then be applied to a diploid to create tetraploid seedlings.

My own attempts at chromosome doubling (using triflurilan) of seedlings at the cotyledon stage have not been successful. Mostly working with rugosas, and I tried with some of the Ole, Lena, and Sven series of compact, hardy, multiflora types. There have been a few seedlings that appeared to be successful doublings, but they lacked hardiness and disease resistance.


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Re: Some ploidy questions

Post: # 69146Post MidAtlas
Tue Jan 29, 2019 12:40 am

I'd personally love to see an oddball triploid hybrid like 'Agnes' doubled, then its hexaploid form used to pollinate diploid rugosa cultivars and probably assorted other diploids. It's amazing how perfectly healthy 'Agnes' is, given its background (even here in what seems to be the epicenter of all sorts of BS--Washington, DC), on top of inheriting yellow color and having a really pleasant fragrance. The biggest thing that bothered me about R. rugosa descendants back in central Minnesota was their erratic response to winters there, with certain milder winters doing surprising damage to them while sometimes far more bitterly cold winters left them hardy to the tips. Some of the hardiest Explorer series varieties had the same odd issues. Here a big problem for rugosas is cane borers, although that susceptibility could maybe be reduced through breeding and selection (I'm not sure that 'Agnes' isn't already an improvement over others in the class.)

Unfortunately, I'm not too inclined to play with those chemicals, and even if you were to get a branch of 'Agnes' to double, it would probably need to be propagated initially by someone adept at budding.


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Re: Some ploidy questions

Post: # 69147Post philip_la
Tue Jan 29, 2019 11:11 am

Most of the recent research I've seen recently on doubling chromosomes uses Orzalin in their protocol. Has anyone done such using e.g. Surflan? (And how would one convert pound per gallon to a microM solution?)
Philip F.
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Karl K
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Re: Some ploidy questions

Post: # 69148Post Karl K
Tue Jan 29, 2019 12:34 pm

Fagerlind (1958) reported on his experiments in doubling roses. He worked with both species and hybrids.
"It is now a well-known fact that doubling of the chromosome number brings about rather great physiological changes. There are considerable changes in the relative amounts of the substances involved. Amongst other things, there is a relative increase in the amount of water, with consequent changes in suction power and osmotic properties."

I think the pumping up of cells with extra water would account for the brittleness of newly formed polyploids. Fagerlind went on to describe the adjustment that occurs in the relationship between cytoplasm and nucleus that allows the cells to become somewhat smaller while retaining all their chromosomes.

Some of his results are a bit surprising. For instance, some tetraploids were less hardy than the diploid parents. Also, when some "sterile" hybrids were doubled, the resulting plants were less fertile, apparently violating Darlington's law.

I puzzled over these paradoxes, but then I remembered that Fagerlind was working in Sweden. It's cold there. A diploid species may be just able to survive there, while its tetraploid progeny, being a little slower growing, are more prone to winter kill because they don't have time to ripen their wood. Similarly, doubled hybrids that should be fertile, don't have time to ripen their fruit ... even though they might contain viable seeds.

Finally, it is important to note that many of the weakly fertile chromosome-doubled plants became increasingly fertile as they aged.

Karl K
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Re: Some ploidy questions

Post: # 69155Post Karl K
Wed Jan 30, 2019 6:13 pm

david zlesak wrote:
Fri Jan 25, 2019 10:40 am
I suspect the nice balance in features in some genetic backgrounds between the diploid and tetraploid levels help these triploid seedlings stand out more (bit more branching than many of the tetraploid siblings, etc.).
Many years ago I read (I don't recall where) that while Wilhelm Kordes was working the line that culminated in 'Crimson Glory', he was aiming for a darker counterpart to 'Mme Caroline Testout' and 'Lady Mary Fitzwilliam'. He came close, but if the plants at the SJ Heritage garden are correctly labeled, both Testout and Lady Mary are well worth emulating. In fact, I had wondered whether CG could be crossed onto a red Tea to get a better crimson bedding rose. I looked at 'Souv. de Thérèse Levet', but was not inspired to pursue the project.

Karl K
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Re: Some ploidy questions

Post: # 69249Post Karl K
Fri Feb 08, 2019 1:24 am

There is another matter regarding ploidy that should be mentioned ... gigantism. When a diploid species produces a chance triploid offspring, the latter is usually larger than the parent. Tetraploids are even larger. Here's an example showing Rosa macrophylla and its tetraploid form.

However, this gigantism is not entirely stable. Fagerlind (1958) wrote:
 It has on several occasions been stressed that polyploids which occur spontaneously in nature, and among these also those which may be regarded as intraspecific, often diverge more or less strikingly from the experimentally produced polyploids (cf. for instance Müntzing 1936, Fagerlind 1937, Wettstein 1937). The former frequently have better, the latter poorer fertility qualities; the former are often more feebly, the latter more strongly gigas-accentuated. As the cause of the difference one may of course reckon with the selection that in time takes place in nature. The above-described conditions regarding Solanum, Bryum and Rosa, however, open the way for the interpretation that at least in special cases the differences are due to the presence of a rather slowly running auto-adjustment.
In other words, the enhanced vigor tends to decline over time. This is one way that old roses seem to deteriorate. But how fast does the decay occur?
It is possible, furthermore, that the adjustment proceeds at a different rate in different organisms. In the tomato it would seem to proceed rather rapidly, in Bryum caespiticium-Corrensii more slowly, and in Rosa rugosa, which after 15 years appears to be at the beginning of its adjustment, the rate would seem to be still slower. 
For example, 'Gloire de Dijon' (tetraploid) is believed by some to have been a self-seedling from 'Souv. de la Malmaison' (triploid).

In some cases, reciprocal crosses can give different results. Pollinating a diploid by a tetraploid should give mostly triploid offspring. This represents a 50% increase in the number of chromosomes (or quantity of DNA) that the cytoplasm must accommodate. The reciprocal cross also gives mostly triploids, but this time there is a decrease of 25% in chromosome count and DNA quantity. Of course, this latter cross should not suffer so much loss of apparent vigor in the next few decades.

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