DNA marker analysis identified four different types of Kunenbo.
It is Kunenbo-A that is ubiquitous parent of hardy Japanese citruses.

Yes, I got it from you under the name PTxSunki😊
Grafted on poncirus, it is very resistant,  not so on its own roots. It is now 2m tall,hope will flower soon. The leaves of the spring growth are narrow and fall in the autumn, while those of the second,summer flush are wider and keep green during the winter. Both are mostly monofoliate.

In this paper of DNA analysis the spelling is kabuchi ,not kubachi

Since original (USDA Florida) 6-7-2 is monoembryonic, its European seedlings  should be different from mother plant.
Contrary to the original description, my  "6-7-2" of B.Voss gives very small number of seeds (1 per ~10 fruits).
1/3 of them contain green embryos, the rest are white.

The leaves look the same. When young the thorns were also present on small branches, now they are  mostly on the trunk.
My plant was from B.Voss, immature wood grafted on poncirus, first flowering was in 2008.

I am far from Sicily, but my Tarocco (TDV variety) has a nice color already in January

It is  a very old variety, there exist several clones differing in fruit quality and tolerance to in house conditions under very dim winter light in Pavlovo  (56° N).

Ilya.  How many of the citrumelo 5* x  Flying Dragon hybrid seedlings do you have?  I ask because I plan backcrosses of various 3/4 P.t. 1/4 citrus, and I'd like to know how much segregation for cold tolerance there is in the backcross 1 generation.  I will be following your results with great interest.

Last spring I pollinated with FD 20 castrated flowers of 5*, got 6 fruits in autumn, totally with 45 seeds.
It gave 43 seedlings; 12 of them are clear hybrids.

Depending on weather conditions there is some overlap between poncirus and its hybrids  flowering. Otherwise, pollen can be dried and stored up to one year at -20C in containers with  a small bag of silica gel.
Last year I succeeded in getting citrumelo 5* x  Flying Dragon hybrid seedlings, but it was after several years of failures.

No, usually it does not have any smell, but when days are hot and in a full flower, you can percept a very  faint perfume.
Nothing to have with citrus fragrance,   resembling more an old candy box 

For the moment nobody knows precisely the origin of poncirus.
 In the recent article you mentioned they used statistical methods to infer the relations between genomes. They made it both for the main part  of genome residing in cell nucleus and coming from both parents as well as cytoplasmic organelles like mitochondria and chloroplasts that mostly are inherited from the seed parent.
Statistics found some discrepancy between these two analysis  in the position of poncirus relative to other citruses.That is why they made a hypothesis that poncirus comes from the very old hybridization between two only distantly related plants. That happened long time ago and in the nuclear part of the genome the parts coming from these ancient parents were scrambled in such a way that you can not distinguish their precise origin. The situation is different for cytoplasmic part that is inherited only from one parent.

Robert,
It really depends on the variety, some years ago I tried to evaluate the number of monoemryonic germinations in fruits of two ponciruses
Old plant from Jardin des Plantes de Paris



My poncirus (from B.Voss)
You

Some more reading on zygotic seedlings in poncirus
https://www.jstage.jst.go.jp/article/jsbbs1951/36/2/36_2_138/_pdf
https://www.jstage.jst.go.jp/article/jjshs/74/3/74_3_189/_pdf
https://www.jstage.jst.go.jp/article/jjshs1925/63/1/63_1_23/_pdf/-char/en