The Tropical Fruit Forum

Better for what?
I've never considered citrons to be of much practical use, apart from smelling nice (flowers & fruit) and impressing people with the very large fruit and the strange fingered Buddha's Hand.
Perhaps martweb has found this article: Gastronomy and the citron tree https://www.sciencedirect.com/science/article/pii/S1878450X16300014
Strangely, this article makes little mention of the main culinary use I have come across. This is the production of candied peel which is frequently used here in England as an ingredient in the traditional Christmas Cake.
I also remember visiting the distillery on the Greek island of Naxos where citron leaves are made into a liqueur.
See my report at http://www.homecitrusgrowers.co.uk/citrusplaces/naxos.html

If you grow citrus in containers in a 'non-citrus' climate, the container size probably has a greater effect on plant-size than rootstock. Even so, with a short summer growing season, a vigorous rootstock may be better than a dwarfing one.
From the point of view of propagation, some varieties root much more readily than others. If you have enough cuttings, try both rooting and grafting!

Here in England we know it as the Rhododendron Leaf Hopper.
Introduced from USA in the 1930's it is thought to spread the fungus that causes bud blast on rhododendron flower buds.
I have this pest on rhododendrens and occassionally see them sitting on the leaves of my citrus plants. However, I've never noticed any citrus damage caused by them.

There is one fungicide which is said to specifically control phytophthera. This is Fosetyl-Aluminium sold as Aliette. See for instance https://www.cropscience.bayer.us/products/fungicides/aliette
As others have said, the best way to guard against the problem is to avoid saturated medium. Make sure water can drain freely through and out of the pot in abround 30 seconds. I also re-plant with the stem raised a little above the surface of the pot mix, even with the highest roots showing.

Nice to see that there is at least one picture of an Australian citrus!
This C. glauca - Desert Lime - was grabbed from the video at about 50 seconds.

Don't forget that Australian Finger Limes have a quite different history from conventional citrus species and varieties. The FLs have really only been selected recently from wild plants which have then been given names - as yet there has been little if any breeding to encourage and select desirable traits. Plants available outside Australia are also quite likely to have been grown from seed or propagated from a seedling and so can be variable.
Conventional citrus are not found wild in the forms that we generally know. They have been selected and propagated for hundreds of years and named varieties are now exact clones of each other with very little variation between individual plants.

I have been growing the fast-flowering Poncirus for many years. In a really good citrus climate in seems to grow OK, but in cooler climates growth is extremely weak. The largest of my plants are still only about 20cms (18") tall. Yes, it does flower before other seedling trifoliates, but the flowers on these small plants are often imperfect and usually do not form fruits. On the rare occasion when a single fruit has formed it has dropped when still tiny. So for me it has failed to be useful for hybridisation experiments or obtaining seeds. Very sad!!

pagnr - a member of this forum in Australia - sent me a useful pdf article about pollination of citrus to produce hybrids. It was written some years ago by Steve Sykes who developed several Australian native hybrids such as the Red Centre Lime (previously Blood lime) and the Sunrise Lime.
Title: Methods used for conducting controlled cross-pollination in Citrus
View at: http://www.homecitrusgrowers.co.uk/pdfs/Citrus%20flower%20pollination%20methods.pdf
Mike/Citrange

To be honest I can't remember whether they have seeds or not.
Although I had a look today, there aren't any fruits left - they all seem to fall together sometime in November.
I'll try and remember to check later in the year!

The whole tree is clearly dying, so the problem is almost certainly at the roots or trunk.
It would help if you post a picture of the trunk at ground level.
Is this a grafted tree or rooted cutting?
And what is the idea of that netting on the ground?
Here are three possible causes:
1.The roots could be rotting due to waterlogging and poor drainage.
2. It is simply too dry and not getting enough water. Once completely dry it can be difficult for water to penetrate and it runs off before reaching the roots.
3. There is restriction of sap flow in the trunk - usually caused by fungal phytophthera infection arising from physical damage or damp soil on the trunk.

I have just a small piece of information linking the names Zehnder and Dunstan which I was told about when researching the origins of a citrus tree in the English city of Nottingham. This quote is taken from my website at http://www.homecitrusgrowers.co.uk/citrumelos/citrumelonottingham.html

However, I did have a lot of citrus seedlings raised from seeds a contact in the USA had sent to me and think this is where the connection comes from. I  received the seeds from a Mr Zehnder who said the parent plant was a citrumelo, not a citrange. He didn’t give me the cultivar name of the parent plant so I initially called the young plants ‘Zehnder Seedlings’ although subsequently he told me that the true name was ‘Dunstan’.

Over the years I have read many reports on attempts to consistently induce early flowering in citrus seedlings. This has always been important commercially in order to develop new varieties. Methods attempted have included choice of rootstocks, height of grafting, hormone treatments, budding another flowering twig below the new graft, restricting sap flow by bending, etc. etc. As far as I know, none of these has been consistently and significantly successful. The exception may be the introduction of early-flowering genes from another species (arabidopsis?) but I'm not sure this has been used outside laboratory experiments and may not be acceptable to some people.
The idea that there is an early-flowering 'hormone' that can be transferred from flowering to non-flowering seedling has often been claimed - and named florigen - but never scientifically accepted or isolated.
I have grown early-flowering Poncirus seedlings for many years. Some seedlings do indeed flower when the plants are still only about 15cms/6" tall, but for me the flowers do not form fruits until the seedlings are bigger. And they are so slow growing that this takes many more years. I have not used them as rootstocks because in my cool climate I need something vigorous.
There are of course many anecdotal reports of inducing early flowering, such as the one by pagnr in this thread using FD rootstocks. He is lucky his FDs are flowering after 5 years - mine take 10 years or more! I also spoke to one French nurseryman who said that standard Poncirus seedlings flowered much earlier if a FD interstock was used.

Interesting climate discussion - even if a little off-topic.
I'm sure much of what you say is correct but nonetheless Britain does very occassionally suffer what we call 'The Beast from the East'. This is when there is a prolonged period of easterly winds in winter originating in Siberia and blowing over northern Europe via Moscow and Berlin. It is usually associated with a strong Scandinavian high pressure system. Passage over water is limited to the English Channel which is only 20 miles across at its narrowest and then provides limited warming of a cold continental air mass.
You talk about Sweden. Remember that the Northern part of the Gulf of Bothnia usually freezes along with the Gulf of Finland and very rarely the whole of the Baltic. This is in part due to the very low salinity - in places the Baltic is nearly a fresh-water lake. In these conditions easterly winds reaching Sweden are isolated from any warming water. I doubt there are any outdoor Yuzus in Sweden!
Here is a photo of the English North Sea fishing port of Whitby Harbour frozen in 2010.