The Tropical Fruit Forum

I planted the ones in the photo in the garden. They also spent the last winter there at -11°C. Most of them survived, but this summer was not good and they hardly recovered and grew very little. Unfortunately, with all citrus the shoots in August are the strongest, in spring the growth is very small. But the late shoots have no chance of surviving the winter.
I still have many seedlings in the greenhouse, I want to plant them out next year. A bit bigger than the last ones.
Overall, most hybrid seedlings have little problem with the winter itself, more with the summers.

I would suggest an Ichangstar parentage...

Interesting that all flowers are on the top. Even the grafted ones.

It is the first time that it lasts so long. Usually they are ripe in winter.
They have the size of a small mandarine. They could be bigger, but my tree is small.

how can you recognise polyploidy? In Passiflora 4n varieties often have serrated leaf margins, like these poncirus leaves here.

the main problem here in Germany is the summers. in my area, a little further north than Till, it's even worse. Poncirus just doesn't like our summers and there is only moderate growth every year. The main sprouting is in July/August, but these branches often don't survive the winter.

@kumin What is Bishop Citrandarin? is it from Alan Bishop?

Mikkel, perhaps you are referring to outcrossing vs backcrossing within the original parents (sweet orange and Poncirus). Backcrossing should narrow the results more than outcrossing would.
The main reason I want to use the segentranges is that they've gone through a very vigorous screening for cold hardiness. The reason I want to use segentrandarins as breeding partners is potential shorter generational cycles, cold hardiness, lower off flavors, and potential earlier ripening of fruit.

In hindsight I suspect US 852 would have been a good seed source. There are a number of tri-specific cold hardy hybrids. These appear to be vigorous in many cases (Thomasville).

                           
I was thinking more of the dichotomy of hybridisations between different citrus species (species hopping), such as Pt x Orange ---> F1 x mandarin --->F2 x pomelo ---> F3 x kumquat ---> and so on
in contrast to backcrossing, where the hybridisations are limited to one parental species.

In theory, I imagine a crossing plan as follows:

F1 cross C35 (Pt x orange)

x selfing

---> F2
mass selection (like you did with the C35 seedlings)

backcross of the hardiest with Citrus

---> F3 
then: mass selection for desired traits

backcross to the same crossing partner like in F2

and so on.

Apart from the time it takes...

I would guess that by concentrating on a few traits and limiting it to one backcross partner, the variance of the offspring can be better limited within the desired traits.

The hybridisation of new Citrus species is also promising, but has the disadvantage that the number of seedlings must be larger, because the combination possibilities are simply more divers and there may be undesirable gene combinations that lead to completely different traits than in the parent species. Ilya once gave an example of sweetness, which is encoded by different genes in 2 citrus species, but the combination of both leads to sour hybrids (I hope I remember the example correctly).

Both has its reason and depends on what is to be achieved. I will do both as there are so many other factors that are involved (e.g. no flowers on a certain plant and the year is lost and so on)
but for a designed breeding program I would prefer a backcrossing scheme.

Wild hybridisation is good to find new types and new combinations.

Do you see a technical advantage in "wild" crossing? Or is it just your choice?
I do both or better I will do backcrossing in the future . But I see more advantages (apart from the long waiting time) in backcrossing, because it is probably easier to plan.

I thought if you already have a F2 (your C35 seedlings) with almost the hardiness of Poncirus, it would be a good idea to cross it with the original Citrus parent of C35. As you have an almost hardy hybrid, but with still inedible fruits, you have already achieved 1 goal. A backcross with Citrus could bring the focus to edible fruits.
If a plant had edible fruits it would make sense to cross it with Poncirus or with C35.
According to the ideal backcrossing scheme
A x B -> F1 
F1 x F1 -> F2S1
F2S1 x A / B -> F3BC1

Fingers crossed that there are already some plants with edible fruit! Just from theory. I would guess that a backcross with Citrus is is a good option with these F2 survivors.

I could not find any citations on this hybrid. Could you post a link to more information?

While searching, I stumbled across this interesting list. Probably all these hybrids are history now.

https://conservancy.umn.edu/bitstream/handle/11299/140015/TB252.pdf?sequence=1&isAllowed=y