Boris
New Member
Posts: 26
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Post by Boris on Jul 9, 2021 2:53:23 GMT -5
Usually, when obtaining hybrids, PT is used as a male parent (exceptions: Morton, Willits, Colman, and Rustic). So it is easier to reject nucellar seedlings in the offspring by mono-leaf. More than one hybrid has not yet reached the frost resistance of PT. Genetic information is contained not only in the nucleus, but also in chloroplasts and mitochondria. Thus, almost all hybrids inherit the chloroplasts and mitochondria of non-cold-resistant parents. Is it possible that part of the frost resistance of PT is inherited by these organelles? Has anyone ever come across such studies?
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Post by pagnr on Jul 16, 2021 22:56:11 GMT -5
I think frost resistance would be multi factorial, i.e. a range of different factors would contribute to it in PT. Dormancy would be one factor, leaf and stem tissue factors would be others, i.e. thickness of layers etc. Plus other factors, FD has a longer dormancy than PT. I am not sure how the chloroplasts and mitochondria might contribute to this. Possibly chloroplasts resistance to damage or mitochondria shutting down in cold weather dormancy. Only a guess ??
According to your question, how do the PT x hardy Citrus hybrids stack up. Yuzu is cold hardy and possibly semi deciduous. When you hybridise PT x Citrus you would be diluting the cold resistance factors in the main genome for a start, with Citrus genes. Even if you could retain the organelles from PT, you might need to get more of the PT genes back by backcrossing or selecting further in the next generation of F2 hybrid seedlings. Some off type Citrange and Swingle seedlings seem to have more PT characteristics than the seed parent.
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Post by mikkel on Jul 17, 2021 10:06:03 GMT -5
In my eyes, it is just as important to choose the right varieties for crossing as it is to apply the right strategy.
Breeding for certain traits is always about crossing, selection and backcrossing. Trees are no different from annual plants. It is only the time it takes that makes the difference. Using Pt as a mother has advantages, but the main work is still to produce F2 and F3 and so on generations, selecting for the best traits. A general pattern for introgression of certain traits into a variety is
Citrus x Poncirus ---> F1
selfing F1 to produce a lot of plants with different genetic recombinations ---> selection for frost hardiness and backcrossing the best with Citrus ---> selection of seedlings for best frost hardiness and backcrossing with Citrus again and so on and so forth. Producing a small number of hybrids is always just a lottery as there are thousands of possible genetic recombinations of the parental genetics. The broader the base to choose from, the higher the chances. This does not necessarily mean that it is impossible to find something of value, but it simply cannot be planned for. A simplified scheme for backcrossing with the assumption that frost resistance is simply controlled by a single recessive gene, which in reality is not the case, but the scheme is the same, then just with several layers of this scheme. in reality there are many possible deviations from this scheme, possible intermediate steps, such as backcrossing with poncirus for higher winter hardiness. and so on. It is just a simplified scheme. the best thing in my eyes is to start with already existing hybrids, that saves already one or even 2 generations. 5Star di Ilya would be an example of a hybrid that can be placed in this scheme in the place of the F2 generation (selfed F1 hybrid offspring), even if it should not absolutely fit this crossing formula. It produces zygote seedlings and is very suitable for breeding. Another possibly even more suitable variety would be HRS899 by Ulrich Bäurer, a Changsha x Poncirus offspring in the 2nd generation. It is hardy like Poncirus and produces zygote seedlings. The C35 F2 seedlings from kumin are also good for backcrossing with Citrus, for those in the US. It would be advantageous to backcross the hybrids with their own citrus parents if possible, as otherwise undesirable gene combinations can occur (but do not necessarily have to occur). for HRS899 U.Bäurer this would be Changsha or at least Mandarin. 5Star di Ilya probably Swingle or a pomelo from the less sour types as there is the possibility that it is offspring of the Chandler pomelo variety. Chandler itself is a hybrid of Siamese Pink pummelo and Siamese Sweet pummelo. C35 seedlings of kumin with oranges (Ruby orange). It makes a lot of sense to deal with crossing strategies, but of course it is not the only way, but it gives a certain predictability. Ultimately, all other crossing attempts are interesting and helpful, but there should always be as many as possible. think big another scheme showing different genetic combinations and the distances to each parent of Citrus x Poncirus hybrids in the F1 generation (Citrandarin and Citrumelo): All hybrids are more or less in an intermediate position, only very few are closer to a parent. In the selfed F2 generation there will be some that are very close to the parents (it depends, as always, on the number of seedlings) for the curious, the whole scientific paper
www.mdpi.com/2073-4395/10/12/1961/htm
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Post by pagnr on Jul 17, 2021 16:47:04 GMT -5
Poncirus X Citrus hybrids such as Citranges, Citrumelos etc are known to produce highly uniform seedlings. This is a major advantage for their use as rootstocks. This tends to continue in further generations. A Citrange rootstock grown out to produce seed, will also usually produce highly uniform seedlings. It may not be exactly the true original "Citrange", but they are clearly the same variety with very minor differences if any detectable. Is this an advantage or disadvantage for further breeding work ? The variation you can tap into would seem to be limited. ??
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kumin
Full Member
SE Pennsylvania, 45 miles north of Chesapeake Bay, Zone 6b
Posts: 113
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Post by kumin on Jul 17, 2021 22:00:26 GMT -5
F1 Citrus X Poncirus hybrids are variable in regards to zygotic vs nucellar percentages within their progeny. For rootstock purposes, nucellar seedlings are highly desirable and are selected as a preferred characteristic.
Breeding for fruiting scion cultivar development has a very different goal, namely the expression of a range of characters. Nucellar embryonic seedlings are a hindrance in the quest towards the expression of recombinant genes.
Excessive nucellar embryony precludes the use of many cultivars as seed parents.
Citrandarin US 852 is a hybrid with ~50% zygotic seedlings. US 1279, US 1281 and US 1282 are additional citrandarins that produce 100% zygotic seeds.
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Boris
New Member
Posts: 26
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Post by Boris on Jul 19, 2021 10:33:35 GMT -5
pagnr, what you are writing about (uniform seedlings) has nothing to do with sexual reproduction and hybridization. In fact, this is a vegetative reproduction from which the F1 generation is obtained again. Come on, guys! You are not answering my question, but telling me about the general principles of hybridization and selection. Perhaps the language barrier plays a role here, and I did not ask my question very clearly. I'll try to describe it in more detail. In addition to chromosomal heredity, there is also a so-called extranuclear inheritance. This is all that the descendant inherits only from the mother organism, besides to the genes contained in the nucleus (in chromosomes). Various vacuoles, cytoplasmic networks, centrioles, and so on. And most importantly, mitochondria and chloroplasts. I believe that other organelles do not play a significant role. Chloroplasts and mitochondria have their own extra-nuclear DNA, which mutates in the same way, but is inherited only from the mother. The question is, are there any genes in these non-nuclear DNA that are partially responsible for frost resistance? Do we lose them when using PT as a father? A cursory study of the issue suggests that there are genes in chloroplast DNA that affect various metabolic processes, the production of starch, lipids, some amino acids, and pigments. There are scientific works on editing the genome of chloroplasts of various plants, as a result of which drought resistance, resistance to herbicides, resistance to diseases and insects were increased. ( Here is the article about the advantages of kumquat chloroplasts in resistance to citrus canker.) But whether there are genes in citrus chloroplasts that affect frost hardiness, I could not find. Mitochondria are responsible for respiration and energy production, and I think their genes can also play an important role in frost hardiness. However, I recently updated my memory of kumin's experience in obtaining F2 hybrids from citrange C35, which apparently have the same frost resistance or very close to PT. And this may mean that all (or almost all) PT genes responsible for winter hardiness have gathered in these hard descendants. And this may be the answer to my question: there is nothing important for winter hardiness in the PT cytoplasm, since the mother of C35 was Ruby orange. But I'm not 100% sure yet.
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kumin
Full Member
SE Pennsylvania, 45 miles north of Chesapeake Bay, Zone 6b
Posts: 113
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Post by kumin on Jul 19, 2021 16:04:15 GMT -5
Boris, you are asking very good questions, which I am totally unqualified to answer. Clearly, in both animal and plant hybrids there is a distinction between parent species serving as male parent vs female parent. E. ferus caballus X E. africanus asinus hybrids differ in varying degrees from the reciprocal cross. Avian hybrids in the case of domestic Cairina moschata X domestic Anas platyrynchos are very distinct from the reciprocal, the female hybrids of the one cross being able to lay sterile eggs and capable of flight, while the reverse are incapable of egg laying, or flight.
Moving to plants, there are cases of successful hybrids in one direction that fail in the reciprocal. Potentilla, Rubus, Fragaria hybrids come to mind.
Poncirus itself is postulated to have arisen in the remote past as a hybrid between a form of Citrus and an ancient, distant relative, hence the trifoliate characteristic.
I suppose there could be a trial evaluating the hardiness of Poncirus hybrids, comparing progeny derived from Poncirus as the male parent vs as the female parent.
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Post by pagnr on Jul 19, 2021 16:22:03 GMT -5
pagnr, what you are writing about (uniform seedlings) has nothing to do with sexual reproduction and hybridization. In fact, this is a vegetative reproduction from which the F1 generation is obtained again.
More than one hybrid has not yet reached the frost resistance of PT.
You are correct. My point was more about the number of crosses you would need to make and number of seedlings you would need to grow to obtain the hybrids, or if in fact the tendency to produce uniform seedlings would be a barrier in further generations. Since your question tended to maximising the frost resistance of PT hybrids, I was wondering if retaining the PT organelles in Hybrids would be successful in itself, without the rest of the PT genes for frost resistance. Or similar genes from Cold Hardy Citrus types.
ps I don't think I was directly answering your question, which is beyond my knowledge.
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Post by mikkel on Jul 20, 2021 7:20:20 GMT -5
you are of course correct that my answer did not directly respond to your question. It was actually more of a monologue of my thoughts on how I personally see the practicality of hardiness breeding at the moment. I hope that wasn't too offensive. If it was, I would like to emphasise that it was not meant to be. Unfortunately, I haven't heard anything more than thoughts about poncirus producing hardier hybrids as a mother plant. What I wanted to point out was that even if the winter hardiness of Poncirus as a mother plant is better inherited, it will still be a question of the quantity of seedlings and the breeding strategy to find the hardy ones. Even with Poncirus as mother plant I would expect that the majority in the F1 will not be as hardy as Poncirus itself. Maybe a bit more than if poncirus is used as pollen parent, but not so high that it would give an hardy hybrid within 1 generation Probably this would have to be done again via several generations and backcrossing. My personal conclusion from Kumin's experiments is that good results can also be achieved with existing hybrids. and that ultimately the breeding strategy is much more decisive. My considerations are purely pragmatic and I think above all about saving time, which each generation costs. It makes a big advantage if there are already two generations. However, I would like to use a Poncirus as mother plant in backcrosses and have already thought about it, but have not yet achieved any practical results.
But these are my thoughts and I don't want to persuade anyone.
Your thoughts are absolutely interesting and I would be happy if you could find out something about it. I haven't found a scientific paper on the subject yet, but I think I might have heard about hybrids with poncirus as the mother. If I find something I will post it.
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Post by mikkel on Jul 20, 2021 7:50:07 GMT -5
pagnr, what you are writing about (uniform seedlings) has nothing to do with sexual reproduction and hybridization. In fact, this is a vegetative reproduction from which the F1 generation is obtained again. It has nothing to do with sexual reproduction in the strict sense, but it means the same for hybridisation work. Pure clones of the mother plant can also be produced from cross-pollinated flowers. In practice, one is faced with the task of finding the hybrids. at first glance, only the monofoliates are recognisable as hybrids, the trifoliates needs further investigation to be distinguished from the clones. The point is that varieties that produce nucellar seeds are less or not at all suitable as hybrid parents.
Especially Poncirus often produces nucellar seedlings, the probability to find monofoliate seedlings in F1 is very low. This further limits the use of Poncirus as a mother plant. You may raise many seedlings that turn out to be only clones afterwards. . It is still not impossible, but the effort is enormously increased.
This is how I understand pagnr's post.
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Post by mikkel on Jul 20, 2021 15:32:48 GMT -5
According to the UC Riverside Citrus Collection -- citrusvariety.ucr.edu/citrus-- there are, for example, Benton, Citraldin (CRC 2619), Citrandarin (CRC 2618), Citrange #1416, Citrangelo (S-281) and a few others that are referred to as Poncirus x Citrus hybrids. They are probably not more cold resistant than other F1 hybrids, otherwise they would be better known.
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Post by ilya11 on Jul 20, 2021 16:54:45 GMT -5
Boris, I guess that you already had an answer when cited historical citranges with poncirus seed parent. They were not generally more frost hardy than reverse crosses.
Frost hardiness in poncirus is highly polygenic, with probably hundreds of genes participating in it. It is probable that few of them are coded in cytoplasmic organelle genomes, but they certainly are not major players.
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Post by pagnr on Jul 20, 2021 17:30:15 GMT -5
According to the UC Riverside Citrus Collection -- citrusvariety.ucr.edu/citrus-- there are, for example, Benton, Citraldin (CRC 2619), Citrandarin (CRC 2618), Citrange #1416, Citrangelo (S-281) and a few others that are referred to as Poncirus x Citrus hybrids. They are probably not more cold resistant than other F1 hybrids, otherwise they would be better known.
They are probably not more cold resistant than other F1 hybrids, otherwise they would be better known. I think some of these you mention were specifically developed and selected as Citrus rootstocks from groups of crossed seedlings, for characters such as vigour, compatibility with Citrus scions, root disease resistance etc. Overall cold resistance may not have been a major factor, beyond a certain hardiness. The rootstocks are intended for use in Citrus growing areas, not the extremes of Citrus cultivation. Potentially more cold resistant types, or even more palatable fruit types were discarded from the seedling pool when the selections took place, as they didn't meet all the rootstock criteria. I did read something about the development research for Benton Citrange, and noted many crosses were grown, and only two eventually selected as Citrus rootstocks. That's from hundreds of seedlings, if not 1000's. Interestingly Benton Citrange fruit are more palatable and fragrant to my taste than other Citrange fruit. They are closer to their mandarin parent, without much of the normal Citrange PT flavours. I think the original work on Poncirus X Citrus hybrids was at first aimed at producing hardy edible Citrus fruit varieties, but moved into the rootstock research area once their suitability was discovered. Unfortunately for us, the main focus of Citrus research is focused on the existing mild climate Citrus growing areas, and on disease resistance for HLB Citrus greening. ( And the curse of Citrus hobbyists worldwide.....seedlessness in fruit )
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Boris
New Member
Posts: 26
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Post by Boris on Jul 21, 2021 1:50:24 GMT -5
I hope that wasn't too offensive. If it was, I would like to emphasise that it was not meant to be. Absolutely, no! I didn't even think in this way. I'm even glad that I got so many answers. I just decided that initially my question was not asked clearly. There is not much time now, I will answer in more detail later.
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Post by mikkel on Jul 21, 2021 10:54:06 GMT -5
Not on the subject of winter hardiness but more broadly on the subject: An paper on the different chemical composition of the fruits of Poncirus hybrids depending on whether Poncirus was the mother or the father.
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