I was reading Paul’s latest entry in his blog (read it here: Paul Barden Roses: 04-07-05: making progress with L83), followed the links and did some extra reading and now have a few questions inspired by it…
I don’t know much about kordesii… I know it is tetraploid and I know it came from ‘Max Graf’ which is diploid… what I don’t know is if there has ever been any work done into how the chromosome doubling occured???
I went and did some reading into colchicine to investigate chromosome doubling caused by the inhibition of microtubules during meiosis… that was pretty interesting… but something else on the wikipedia page for colchicine grabbed my attention:
“When used to induce polyploidy in plants, colchicine is usually applied to the plant as a cream. It has to be applied to a growth point of the plant, such as an apical tip, shoot or sucker. Seeds can be presoaked in a colchicine solution before planting. As colchicine is so dangerous, it is worth noting that doubling of chromosome numbers can occur spontaneously in nature, and not infrequently. The best place to look is in regenerating tissue. One way to induce it is to chop off the tops of plants and carefully examine the lateral shoots and suckers to see if any look different.[11] If there is no visual difference flow cytometry can be used for analysis.”
The part in bold is what I was interested in. I guess they are essentially inducing sporting. Did kordesii appear from diploid pollen from diploid tissue or did it appear from sported tetraploid tissue on ‘Max Graf’, or is this information not known? This goes back to something I was interested in a year or so ago regarding inducing sporting from secondary axillary buds by chopping the stems back and then rubbing off the regenerating primary axillary buds to force the secondaries (see this link again: http://www.amjbot.org/cgi/content/full/87/3/355). If the fidelity of meiosis is ‘not as good’ in the secondary axillary buds as in the primary axillary buds is it reasonable to predict chromosome doubling of diploids could be forced to happen more often to produce more fertile, tetraploid, species crosses to bridge that fertility gap that often occurs when species crosses (esp. wide species crosses) are done?
Hi Simon,
That is a great question. Rosa x kordesii is a seedling of ‘Max Graf’. Kordes reports it is a self. Perhaps he assumed so, perhaps he self pollinated the flower, etc. However, the evidence of a semi-double to double bloom of Rosa x kordesii is very strong, overwhelming evidence that it is not a self. Double flowers (greater than 5 petals) is dominant to single and ‘Max Graf’ is single. There was likely a 2x egg in a MG flower and some pollen from a nearby tetraploid is what fertilized that special egg.
I have mass pollinated ‘Max Graf’ over many years and raised the seedlings. One seedling is my 3K20 that I shared seed and plants of with others. It is tetraploid and highly fertile. 3K20 likely has ‘John Davis’ as the male parent from the physical features. I have also got a 2x seedling with MG pollinated by a polyantha and shared plants of that too. That one is far less fertile.
Pollen or eggs that do not have a reduction in chromosome number compared to the parent is a relatively rare, but common phenomenon that allows plants to increase in ploidy. In such wide crosses like MG, unreduced chromosome numbers is often the method that leads to a little fertility in such nearly sterile plants where meiosis and getting good chromosome pairing and balanced gametes is very challenging. Also, unfertilized eggs, etc. that develop into embryos can bring the number back down again in species.
Wide temperature extremes can interfere with spindle fibers and arrest cells part way in mitosis and lead to cells after things normalize and go into another mitotic cycle to have doubled chromosomes. It happens very rarely I suspect and in more inhospitable climates.
Take Care,
David
P.S. I published a study where I compared trifluralin with colchicine for chromosome doubling. I obtained better results and this chemical is less toxic to humans. There is a lot of work out there with a similar chemical to trifluralin called oralzalin. These are both commonly used as preemergent herbicides to prevent mitosis in germinating seeds. They are not very water soluble and stay near the soil surface.
David said: “There was likely a 2x egg in a MG flower and some pollen from a nearby tetraploid is what fertilized that special egg.”
I’m inclined to believe this as well. When ‘Kordesii’ came along, Kordes proclaimed it a new species based on the fact that self seedlings all looked the same. If that was all that was needed to qualify a cultivar as “a new species” then we could almost call ‘Little Darling’ a “new species”! (well, not quite)
Could we also call Basye’s Amplploid a species also in this case? What is the full definition of a species anyways?
I don’t consider neither Basye’s Amphiploid nor r. kordesii as species because, to me at least, a species occurs in the wild. Instead, I believe them to be cultivars from species roses.
This season, I’ve used a seedling of kordesii X the amphilploid-- and crossed it with another related seedling, (a swamp rose x amphiploid). Who knows what results will come because both are very different despite being similar in parentage.
What’s truly funny is that Max Graf itself could theoretically be created in the wild (Japan). lol, --but unlikely that Kordesii could be.
Ok… regarding the 2x ovule… Was it due to some ‘malfunction’ in the meiotic process that prevented segregation of the chromosomes in diploid plant tissue or was it because the growning point the flower was made on had sported previously to become tetraploid and could routinely produce 2x pollen? I don’t suppose this is known???
Simon,
My money is on a “malfunction”. Mind you, I think there are many “malfunctions” that occur during sexual (and asexual) reproduction in plants that are all part of the evolution mechanism. Its not as if something broke, per se, but rather a rare mechanism kicked in and threw a genetic spanner into the works, and out came something new and unique. In a natural setting this may have survived to become a new population that stabilized into “specieshood”, or it may have died as a weak mutation and taken its novel genes with it. However, a human noticed it and made use of it, ensuring its new genes survived.
And so was born the hybrid tea LOL sorry…
That’s kinda what I meant by putting malfunction in quotes… all part of the blind watchmaker’s grand scheme 
I think it would be really interresting to see if we could ‘force’ some of the diploid species crosses to mutate and form tetraploid specimens by really hard cutting back etc… like I need another project rolls eyes
How common are NATURAL “ploidy-sports” of roses, for want of any other better description? (eg tetraploid rose sports a diploid branch, or the reverse)…is there one example of where this is known to have occurred without human interference?
Great points Paul!
That is a great question Simon we cannot answer with 100% certainty. Unreduced or more appropriately called, 2n gametes, occur frequently enough though. THere are different mechanisms that lead to them. There are even 4n gametes. The original megaspore mother cell (and microspore mother cell too for pollen formation), has its DNA duplicated. Upon two key divisions 4 gametes are obtained typically that have half as many chromosomes as the parent plant. Upon these different steps there can be premature cytokinesis as well as parallel spindles just to name a couple things that can happen to result in a gamete that has twice as many chromosomes as the parent. Most typically the gamete that has the chromosome number of the parent plant is not exactly like the parent plant. THere is a little bit of recombination between chromosomes and relative to the parent some chromosome sections that are duplicated and some that are missing then compared to the original parent plant. As part of my Ph.D. research I looked into ‘Daydream’. It is reported to be a cross of ‘Lavender Dream’ and ‘Henry Kelsey’. I used AFLP markers and learned there is no unique fragment in it common to HK and missing from LD. DD and LD have some slight differences in banding (mainly a relatively few missing bands) likely due to recombination of the chromosomes and some arms duplicated and/or missing. ‘John Davis’ of course is a triploid, but tends to produce most of its pollen in the diameter range expected for a tetraploid (2x pollen). Other seedlings of Max Graf were tetraploid too. I suspect 2n eggs is relatively common in Max Graf. In addition, I found the same true for ‘Robin Hood’. In the literature there are 4x offspring from it. I made crosses of it with 4x males and acquired a number of 4x offspring. The rate of 2n gamete production is influenced by environment and also the parental genotype can be more or less prone to it. THere are some (primarily recessive) genes that tend to allow for the potential for things such as parallel spindles and premature cytokinesis documented in other crops. In my potato research I looked at genotypes able to produce 2n gametes and followed the rate of 2n pollen formation across years and environment. It varied, but generally genotypes able to produce them produced them to some degree over time.
Spontaneous chromosome doubling of somatic or vegetative tissue of course is possible, but there is such a strong precedence for 2n eggs in Max Graf that it is very plausible and highly likely that is the mechanism by which R. x kordesii was able to come into being.
There are roses that routinely produce some 2n pollen. Looking at pollen diameter, for instance, these include ‘Morden Blush’ (a tetraploid with some pollen large enough to be 4x) and ‘Topaz Jewel’ (a diploid with some 2x pollen).
If we want to take advantage of the different sized pollen grains for instance, there are mechanisms for sorting pollen by size. I never have done it though and it sounds like it may be a bit tedious.
Sincerely,
David
Unless you were looking for it I would imagine they’d be really hard to detect.
What I meant was I think it would be hard to determine how common natural ploidy sports were because they would be hard to detect and I doubt if anyone is even looking… but if you think about it we have diploid species, tetraploid species, and even pentaploid species (are there others???)… they had to occur somehow… maybe they occured through somatic cell mutations… Dr Basye was working with a tetraploid version of bracteata (code named ‘Cyt 127’… not sure what that means though)… I wonder how that appeared?
I read soemwhere that roses that were artificially doubled in chrmosome number looked fairly disctinct from their halved originators, no?
Henry has a cultivar of Rosa acicularis nipponensis that he thinks could possibly be tetraploid even though the species is diploid. The leaves are much, much larger.
I cant find the link of Henry’s right now, but it shows the foliage disparity.
David,
Has anyone studied any of the highly fertile triploids to determine if there is a difference between the percentage of 1N and 2N eggs, VS the percentage of 1N and 2N pollen grains? I’ve wondered about the behavior of ‘Golden Angel’ in this regard, since it is extremely fertile both as a seed and pollen parent. I sometimes get up to 25 seeds per hip and often 95% germination. (Remember, triploids are usually sterile! LOL) Is there any reliable technology to measure such values? Is there any point in looking for this data, or is it not likely to be useful? Whaddaya think?
Paul
That’s a great question Paul. Not that I know of. Ovules are very difficult to clear and work with to isolate and count chromosomes. There are just so many more pollen grains being formed and easier access to them to study. People typically rely on the ploidy of offspring and make inference to the ploidy of eggs. For determining ploidy of pollen in triploids, doing in vitro germination tests could help. Triploids typically have a low rate of pollen germination like Leen Leus looked at in her thesis. We just apply a lot of pollen to overcome that and often pollen at a higher ploidy level can have greater vigor and get to the egg sooner. Heavy pollination may select for a higher rate of 2x pollen participating in fertilization than 1x pollen. We can look at the pollen that germinates (shows viability) in assays and if it is early in the process, etc. we can look at the size of each grain that germinates and get an inference of ploidy based on that. The ones that are aneuploid and likely dead or incapable of germinating we can omit from our study. The aneuploids that can germinate would of course be counted and would likely be near having complete sets of chromosomes and we can infer the ploidy they are closest to. Aneuploidy in roses is relatively rare anyways and such grains may not participate in fertilization and the generation of viable offspring that readily or there may be some corrective measure the embryo/plant undergoes to make complete sets later.
I think it would be great to pollinate GA with a diploid that has very uniform pollen size and a tetraploid male with very uniform pollen size typical for its ploidy level and look at the relative ratios of ploidy levels among the offspring. There is some evidence that there is preferential embryo development (yet not complete) from gametes having the same ploidy level. This would be a great test to help infer the answer to that question as well. Would you be up for it Paul?
Take Care,
David