Meiwa seems to be very polyembryonic (100%?). Not sure if it is any use as the pollen parent.

Hydrobell and pagnr thanks for commenting and the info. From my own small experience I observed Meiwa was at least 70% polyembryonic, with the vast majority being 2 embryos per seed and occassionally 3. Calamondin is 100% polyembrionic with up to 5 embryos per seed.

quote " meiwa is 70% polyembryonic "
I should have said 100% nucellar, (clonal from the parent), not necessarily also 100% polyembryonic, (multiple embryos per seed). I don't think there are any zygotic seedlings produced from meiwa seeds, I have never found any variation.

Nagami seems to produce zygotic seedlings, never seen Reale so don't know if it is zygotic or nucellar, or combination. Hopefully pollinating with foreign pollen may overcome any self incompatability/genetic barriers that prevent the Meiwa from producing variants . There may be hidden zygotics produced that never get pollinated, so never develop to seed stage ? Also single seedlings could still be "polyembryonic", if the other embryos in the seed died. True zygotics should be at least somewhat variable, even if self pollenated.

Thanks for the great info pagnr, I find hybridization discussion fascinating. I have a small kumquat tree a foot tall which I'm certain is Nagami (it was labelled "Meiwa" but the fruit looked and tasted exactly like Nagami bought from the store), I will use that also in future hybrid attempts.

Is it possible to store citrus pollen for future use when cultivars are flowering at different times?

quote," pollen can be collected by drying non-dehisced anthers from unopened flowers over silica gel at room temperature. The dried pollen can then be stored in vials at 4'C until needed. Stored pollen can be applied to the stigma of the female parent via a soft paintbrush."

The reason to keep away from open flowers is to avoid any extra foreign pollen that was transferred in by insects before you arrived with your brush. If you have many different Citrus flowering and high insect activity, there may be multiple pollen types already on your target flower. Then your A cross B, will actually be A cross X?.
In reality this is probably unlikely, depending on the actual flowering and insect activity at the time. and you can isolate the pollen parent plant or bag pollen source flowers and use the naturally released pollen.
However if you want to be 100% sure of A cross B, you should follow procedures.
Not sure if there are any other reasons to use non dehisced flowers. Perhaps the "immature" pollen stores better, I think released pollen has a few hours/days short life in the open air, so probably it may already be half spent in many cases if collected from open flowers?
The other storage/ pollen life questions are probably much the same in other vegetable crop breeding, Capsicum, Eggplant etc ??? From memory pollen has a reasonable storage life, but as for seeds, the kitchen fridge is not always ideal long term.

here are some general quotes from Carol Deppe, "breed your own vegetable varieties"1993
"most pollen becomes viable just shortly before the anther dehisces(sheds it) In general, it is normally maximally fertile and viable right after it is shed.
Some pollen continues to be viable for several days, other pollen is dead within a few hours.......freshly shed pollen is moist looking and more brightly colored than old pollen

"some kinds of pollen can be stored for long periods, and some can't...
when I want to store pollen for just a few days, I usually put freshly shed pollen or even whole flowers that have just shed pollen in a vial or plastic bag to prevent them from drying out. Then I put the container in the fridge.
Most, though not all,pollen will keep for a few days to a week or two in this fashion.
When I want to store pollen for longer periods, I usually desiccate and freeze it. I put the pollen( or anthers with pollen ,but without the filaments)
in gelatin capsules(kind used for drugs and vitamins, many but not all pharmacies sell empty gel caps, ?pagnr says health shops?
I put the open gel caps on a layer of silica gel, seal the jar, and leave it at room temp for a few hours. Then I open the jar, close the gel caps, put them in a vial with more silica gel, cap it and put it in the freezer.
To do a cross with frozen pollen, I open the vial and remove one capsule. Then I open the gel cap andleave it lying around at room temp for an hour or two at room temp so that the pollen or anther can rehydrate before I use it."
pagnr says, this is general info for hobby plant breeders, covering a wide variety of species. Citrus is probably not any harder than most crops, but it may be worth more research about it's specific techniques.

Pagnr thank you very much for the information, much appreciated. I will try both methods you posted next time my citrus flower. I will definately keep looking into this. If I find more info I will post it here.

Update on the cross pollinated fruitlet. It is still the size of a pea, hasn't grown any bigger, but it is now turning orange. When I bought the tree last year there were fruitlets like this already on the tree and they never grew and eventually fell off. I hope this doesn't happen to this fruitlet!

Update: the fruitlet is now completely orange but it has grown a little. Hopefully it will grow to full maturity and produce some seeds for me to plant.