The Tropical Fruit Forum

Thank Ilya you for your interesting report.

The picture of the entire plant is interesting because it shows the variety of growth forms and thorn development. Taken together, these are all characteristics that my several, even smaller plants also exhibit, sometimes only individually.

As for the fruit, it seems to be mostly a pure mandarin, so few Poncirus cells are recognizable in the chimera... However, the thickening of the peel indicates a disorder, possibly PT cells. Have you tasted the peel, especially at this thicker spot?

What were the coldest temperatures your plant has already withstood?

Thank you,
Indeed, everything is twisted in this variety, so no wonder the peel is not uniform.
I was always intrigued by the absence of trifoliate taste in its fruit reports.
The smell actually is of pure satsuma and neither albedo nor flavedo do not have any special notes, the bitterness is on the level of satsuma peel.
The same  can be said on the taste of central white region that is a part of vascular system, supposed to contain only poncirus cells.
I have had Prague since 2002, bought a  very small plant grafted on PT from B.Voss. It was in open since 2003, never protected , experienced many episodes with  frozen grounds, the lowest temperature was -16C in 2012, when it lost the tips on a new summer growth.
It was flowering but no fruits and stayed very small.
I never observed any pure poncirus or satsuma stems on it.
In 2016 I regrafted it on 1 m high poncirus stem, grown from the seeds sown in situ. Last year it brought the first fruits, that were ridiculously small. So, this year it has been its first harvest. The lowest temperature since 2016 was -11.5C.

Marcin,
Is it possible that your Karel Mundl plant is this one:
"Kolín"
A few years ago, Karel Mundl received trifoliate fruit from Kolín, which was also practically bitter-free and very edible. Unfortunately, the owner of this plant from Kolín has passed away, so the future of this plant is unknown. If anyone has further information about this Kolín trifoliate, or the possibility of obtaining seeds or grafts, I would also be interested.

Posted by Jibro here: link

I  had for many years Ventura lemandarin in a pot and was rather disappointed  by the smallish size of its fruits.

This year I have its first harvest from open ground plant (5star citrumelo graft).
 

Largest fruit:


Smallest one:



Very pleasant unique smell, reminds Keraji with something else (Yuzu?), bitter flavedo, moderately bitter albedo.
Fruit peels easily, many  white seeds, very juicy, non bitter, 12°Brix, no aftertaste, good ratio sugar/acid, can be eaten out of hand.

I guess Sylvain called it OPTaichang, a seedling from open pollinated
Taichang.
Funny that its first fruit was deformed, probably by flower mite infestation.

http://pafranceparamoteur.free.fr/datas/perso/Agrumes/temp%204/Taichang%20lemon.png

I don't know, but high grafting on the strong root and fixing new growth upward is very helpful.

I think it would be an interesting and exciting cross, if possible. I wonder why no attempt has ever been made. It seems like it should be possible with a blood orange or a red pommelo.

https://tropicalfruitforum.com/index.php?topic=52897.msg509721#msg509721

You have a good eye.
It is Frontenac, hybride of V.riparia and  Landot noir. Completely resistant to phylloxera and fungal diseases here.

Yes, it is definitely working to force non-stop grow of young seedlings.
Also,high humidity prevents red mite infestation.

Up to the four true leaves nucellar seedlings of it are mostly monofoliate.

Quote from: Skandiberg on July 23, 2025, 12:45:47 PM

I would have expected some trifoliate ones from that cross.

I think it's far enough removed that the trait didn't get passed on. CL4s are only 1/8 trifoliate, even US-119, which is monofoliate, is 1/4 trifoliate.

Trifoliate leaves are definitely a multi-gene trait, since it doesn't follow Mendelian inheritance (often becoming a different trait with mixed mono and trifoliate and/or bifoliate leaves in the second generation). There's something about it that is a true dominant gene, since every F1 trifoliate hybrid has trifoliate leaves, but after the initial cross it stops behaving Mendelian.

Still, the majority of my F3 exhibit at least occasional bi-tri foliate feature.

It is well known that winter hardiness in poncirus is multigenic with at least 6 gene regions situated on different chromosomes.
When present together, they are responsible for its resistance of -24C. 
One need many generations  and high number of seedlings to keep them together and simultaneously introduce genes for large fruit, high sugar and absence of nasty taste from cultivated citruses. On the top of this,  these traits are also multigenic.
This does not exclude serendipitous finds, but most probably will be achieved only by the methods of genome engineering that are beyond the means of amateur hybridizer. 

Two years ago I succeeded  to make a cross of PoncirusPlus with Valentine that had the acidless pomelo as a mother.
https://tropicalfruitforum.com/index.php?topic=52897.msg509721#msg509721
The seedlings are growing nicely, some of them are now one meter tall.

Your "acidless orange" is probably something else.
I have two of them- Meski from Tunisia and a French variety Gosset, their seeds do look exactly like those of a normal sweet orange.