Just thinking, the usual way of creating Citranges/Citrumellos etc has been to pollinate from Poncirus into the sweet Citrus type ( orange, mandarin etc ) and then screen for trifoliate type seedlings as the obvious hybrids.
However, there should also be unifoliate hybrids possible from the same PxC cross, which may be harder to discern from either off types or other accidental crosses. These may be better candidates for acceptable fruit types, especially if there is any genetic link between the trifoliate character and bitterness, leaf oil types, etc.
Is anyone aware of any unifoliate Citranges/Citrumellos etc, or 2nd gen unifoliate types ?

http://www.citrusvariety.ucr.edu/citrus/citrumelo_3821.html

this says there was Pentafoliate as a young seedling, how is that possible?

It is sometimes seen that a Citrus plant can throw some trifoliate leaves, or a Citrange etc can throw some unifoliate leaves. It is a matter of a gene being switched on or off during growth.
Many Citrus relatives are trifoliate or pentafoliate, so those genes are probably in all Citrus but turned on or off and not expressed, except by accident or in hybrids where the switch is cancelled out.
I would guess it is turned off, but that probably depends on what the ancestor of all the Citrus relatives looked like ( unifoliate or tri/pentafoliate )
A pentafoliate seedling must have the gene switch turned on or off in later growth.

I had a seedling tree that originally produced some pentafoliate leaves. I posted it on the forum some time back. However, the tree no longer produces any pentafoliate foliage. Why it did as a VERY young seedling, now none, I have no idea. - Millet

I have three Swingle seedlings that produced a few pentafoliate leaves last year. At that time they were about a foot high. This year none have shown up. It could have something to do with the weather or environment, as those leaves developed toward the end of the growing season.

When I read what Dr. Brown did and what Swingle and Webber did then I come to the conclusion that we have to go in a different direction than they. The dream of a F1 cross with good fruit qualities seems to be not more than a dream. Whatever nice citranges we have obtained it is not what people have hoped for.
My idea is that we might do better when we go in the opposite direction of the previous breeders: We should try to breed good fruit qualities into Poncirus not to breed frost hardyness into normal citrus. Or with other words: As much Poncirus as possible. That sounds crazy. But let me explain my theory. I think that the adaption of Poncirus to cold climate is so perfect and so complex that we never get its full genetic programme into a normal citrus within a few generations. And without the full programme we will never come to an hardiness of -20°C, so I assume. But it might be easier to breed some of the good fruit qualities into Poncirus or breed the most offensive aspects of Poncirus taste out.

> We should try to breed good fruit qualities into Poncirus not to breed frost hardyness into normal citrus.
What do you mean in practice? Back cross F1 with PT?
Back cross F2 with PT?

Hello Greg, it encourages me that you are with me. Hope we have one day something selfbred to exchange.

To your question Sylvain:
I want to make it more probable that all the hardiness genes necessary come together in one plant. Therefore I want to cross F1 plants back to Poncirus and also hardy F2 plants back to Poncirus. Thereby I create plants with over 50% of Poncirus genes. It is very likely that those plants have fruits much like those of Poncirus (so Swingle about cicitranges). But that may change in the next generation. Therefore I plan to create another generation by selfing with the F2 and F3 plants. So I plan with two generations. Might be doable in 10-15 years. And as far as I know nobody has done it before.
I hope that plants with more than 50% of Poncirus genes also produce more zygotic offspring than citranges. (As a rule fertility increases when the two cromosome sets are more similar. Hope that is also the case in these crosses.)
What I want to do sounds like a very frustrating long term programme. But I expect that the backcrosses with Poncirus will already be interesting. We have for instance a Segentrange in Europe, called Sanford Curafora, which can withstand -12°C and has good fruit. This plant crossed with Poncirus might give us Citrandarins which are hardy close to -20°C. I would be glad to have such plants even though the fruit might be good for nothing else than a lemonade or marmelade. Wish me luck! For I am crossing Sanford Curafora at the moment. Hope I get some seeds. Unfortunatelly the plant is said to have every few seeds if any. (If I don't succeed I cross the opposite direction next year.)

Till,

Do not quite understand what you are trying to achieve crossing citranges or citrumelos with poncirus. Fragrant hardy decorative poncirus? These crosses even theoretically will never give edible hybrids with poncirus level hardiness.

Both hardiness in poncirus and "good" smell and taste in citruses are determined by dozens of genes spread all over genome.
Theoretically, they can be separated and combined in one plant by crossing several poncirusXcitrus F1 plants and selecting among thousands, may be even millions of zigotic seedlings.
This is in parallel with what modern hybridizers of garden roses are doing in order to get new breeds. Kordes in Germany is selecting few new varieties out of millions seedlings.

Taking into account scarcity of true zygotic mothers among F1 poncirusXcitrus hybrids, long juvenile period and large size of citrus trees a similar program for hardy citruses will require a huge investment.
The cost can be reduced only if DNA markers both for hardiness and "good" taste are known, so the selection by culling can be done early. But for the moment we are rather far from this understanding.

Of course just serendipity can some time work, so it is still worth to try like Dr. Brown and others have been doing in the past.

Ilya, I think your numbers are quite right...maybe millions of F1 x F1 crosses to get all the traits in one generation. Not possible for me to do so not a goal. I expect it to take thousands of plants from that kind of cross to get to just Poncirus like hardiness. That is possible for me and so I will select for just that trait initially to build a gene pool. These plants will then be crossed with relatively hardy decent flavored plants to create a second generation of plants that be crossed with each other to create a third generation that will be screened for Poncirus like hardiness. Long process, but from that last pool of survivors I would expect to find some good flavored fruits from hopefully a manageable plant population.
In parallel I'm trying to backcross some F2s to the first year flowering Poncirus hoping to get some relatively hardy crosses. I hope that the early maturity genetics are not recessive, otherwise it'd be another generation before that trait returns...but still worthwhile perhaps.

My focus is not on the first generation, i. e. on Poncirus x citrange or Poncirus x citrumelo. My focus is on the next generation created by selfing. You are certainly right, Ilya, that I cannot bring all interesting citrus features together by this method. But if I have a poncirus with better smelling flowers then it would be great already. However, my aim is at good fruits. And here I would say:
- Fruits without resin taste are my minimal goal.
- Fruits without resin taste and bitterness would be great.
- Fruits bitter but sweet and without resin taste are also welcome.
- And fruits without resin taste, without bitterness, and sweet would be the non plus ultra.
I am quite optistic that I reach at least my minimum goal and probably also more.
I do not know whether I need millions of plants. I suppose your calculation is too pessimistic because it does not take into account that we can narrow down the number of plants by good selection in each generation. And some people have already done great work in that field in that they left us interesting Segentranges. Take your Swingle 5* or Sanford Curafora. If I manage to reproduce within two generations the absense of resin that Sanford Curafora offers me but add hardiness then that should be possible.
And if I use monoembryonic Poncirus plants then there is much hope that I get some more zygotic seedlings then we are used to from the first generation.
What I want to do is very much like that Greg is doing: I select plants with interesting treats and try to combine them: For example a decidious hybrid with sweet fruits would be great even if it has not full hardiness. I could combine it with plants that have the other features.
Or other things might be interesting: If, as you and Dr. Brown observed, Citrus ichangiensis eleminates off flavors in Poncirus hybrids then it might be interesting to cross them back to Poncirus and see if the genes suppressing the off flavors are not equally active in a more than 50% Poncirus hybrid. And that could already be one deciduous and quite well adapted to our climate. You see even if I do not manage to breed out certain undisireable genes it might be that a certain gene combination silences those genes I do not want. And only the result is what counts.

Yet, I agree everything depends on chance or God's grace. I cannot promise anything. I can only make certain combinations more likely. And I am just beginning with my experiments. So much too early to make bold claims.

What regards the long juvenile phase, I hope very much with Greg to get the early flowering poncirus and that the early flowering feature is dominant in its offspring. If I do not get it or it does not help me then I still do not expect to wait for more than 5 years. Dr. Brown brought all his trees to flowers within 4 years by the admittingly not nice technics of wire girdling. I can try to graft mature twigs into the plant to stimulate its maturation. And I can try what Bernhard Voss recommends in his book: Grafting on Poncirus or better: grafting on a Satsuma which is grafted on Poncirus. He says that plants on Poncirus are blooming within four years and those grafted on Satsuma (which is on Poncirus) within 1 year. Since I have no experience with these technics I have to be skeptical that they work in all cases that I wish. And I am quite sure they don't. Yet, they will help sometimes and sometimes is perhaps enough. That is at least what I hope.
But is project is abig one. If we work together (by pollen exchange for instance) we can archive something. What we can archive at least is to make the work easier for the next generation of citrus friends having the same goal.

Most probably if, and when, a good tasting and very cold hardy citrus variety is ever developed, it will probably be through gene splicing, and or incorporating genes from some foreign plant species into a citrus tree. Thus making a biotech GMO-citrus cultivar. I doubt that it will ever ever come about through Poncirus. An example of how this can work, Greening disease research has produced a citrus tree that is resistant to the Greening disease by introducing a spinach gene into the tree's chromosome. Perhaps a foreign gene could be found that induces cold hardiness to cirus. - Millet