The Tropical Fruit Forum

What would be some good cultivars for starting a cold hardy lemon

Maybe if someone bred citron with yuzu and then crossed that with ichang lemon.

I need a variety that is either not male sterile as I could use it as pollen parent for crossings ...

Most "male sterile" varieties are not completely absolutely sterile and could probably still be used as a pollen parent in controlled crosses, I think.

or is monoembryonic and can be used as mother. At least a part of the outcome should be seedless.

Many polyembryonic varieties could still be used as the fruit parent, since a small percentage of the seeds will still be zygotic. Identify any monoembryonic seeds for best chances of finding a zygotic (resulting from sexual recombination) seedling.
It is just more difficult and inconvenient, since many of the seedlings you are growing will turn out to be genetically identical to the fruit parent.

Also do research about citrus breeding and look up what was used for the crosses. Kishu and Clementine have been used as the fruit parent in crosses. Also Temple oranges.
Any pure species, like pomelo, kumquat, citron, Ichang papeda. These do not produce nucellar (exact genetic clone) seeds.

How is Yuzu compared to Meyer, especially also the rind?

An analogy can definitely be drawn between Meyer lemon and Yuzu, but they are also totally different.
The analogy would only be because both of them are somewhat like a lemon but much more on the "orange" or "mandarin orange" side of the flavor than a regular lemon. If a regular lemon is "yellow color" in appearance and flavor, then Meyer and Yuzu would be more in the "orange color" direction. But that is pretty much where the similarity ends.

I would say that Yuzu has some unique fragrance that Meyer lemon does not have. Yuzu is also poor eating quality due to being packed full of a huge number of large sized seeds, the interior flesh not being very juicy, and overall containing only a very small quantity of juice. But the outer rind/peel of Yuzu is tender, mostly lacks bitterness, and I would say is edible or somewhat edible, definitely to a much greater degree than the Meyer lemon. The white pith of Yuzu lacks bitterness and some might even describe it as "sweet". Whereas with a Meyer lemon, you can make a zest from the outer peel but you probably do not so much want to include the white pith, which is nearly useless and has some bitterness like any normal lemon.

In my opinion, a mix of pressed oils from Yuzu peels mixed with the juice of an ordinary lemon would probably be superior to a mix of both the juice and zest peel from a Meyer lemon.

With a Meyer lemon, if you use the peels you are probably going to want to grate and zest it. With Yuzu, they are tender enough that you can simply very finely slice the peels or just mince them. I mean they do not have to be cut up as fine.

This article may give you some feel for how complicated and little-studied this issue is
https://www.mdpi.com/2073-4395/11/10/2023/pdf

The picture looks to me like the type of thing you would get if you crossed a lime with a citron (I mean a lemon with more C. medica ancestry than the usual lemon).

These were to comments made to the video-

"You are probably right about the 1st one, It's just a lemon but a 'desi' lemon and desi fruits are considered the one's grown in villages as apposed to the commercially grown ones. 2nd one is, as the other people pointed out is gondhoraj (gondho means smell/fragrance and raj mean king/royalty so basically king of fragrance), and the third one is kagzi lebu"

"Bangladeshi here, these are all recognized as different varieties of lime. B is called elachi lebu and C is called kagoji lebu in our regional dialect. these are used as you'd normally use lime, for enhancing the taste of curries and daals, for teas etc. My mom loves to use C for lemonade because it's very fragrant. also, we only eat the rind of B as it is very thick and less bitter, goes great with rice and curry."

Some additional (low resolution) pictures, so you can see how some of these look in the winter.
Pictures taken January 15, 2022

Here is what the leaves on the Sudachi look like


Ichang papeda


I planted a rooted cutting of Changsha right next to a Yuzu seedling to see how they would do. They are right next to each other. Both are less than 10 cm tall, and they are planted not too far away from the house.

small Changsha (on own roots)


Yuzu seedling (on own roots)


There's another Changsha that's planted in a more protected spot that is bigger and has leaves that look just fine right now. (I believe that one is on grafted rootstock) Interestingly, the leaves on 2 of the other Yuzu bushes (on grafted rootstock) look fried, while another looks bad but the leaves look slightly less than totally burnt. It seems inexplicable, except maybe these Yuzu bushes were just more exposed, did not have the benefit of snow cover.

The leaves on the Bloomsweet are starting to show the effects of the earlier cold now, do not exactly look healthy, but they look like they will survive.

I've visited the nursery on Sauvie island, which the article refers to. The owner tells me he can even grow Satsuma mandarins outside unprotected. Apparently because the island is located in the river surrounded on water on all sides.

I gave them some rare hardy citrus varieties that I was told they were testing in their grove. (Although the skeptical part of me worries they did not take very good care of them or pay much attention to them, and they may not still be alive, or they may have lost track of them)

But I think hardiness is therefore also limited for planting in ground at my zone 7 place, without more protection.

I am pretty sure Nippon Orangequat is not going to be able to survive zone 7 in Germany without protection.
I remember someone did an experiment and planted a kumquat just outside of Atlanta (US state of Georgia, zone 7b), and even covered the plant with frost cloth, and it did not survive.

Thank you, maesy, for those very interesting pictures from Switzerland.

I can provide an update now, January 13, 2021

Most of the Yuzu leaves look half-fried. I can tell the leaves definitely suffered some freeze damage. It looks bad, but the leaves are still sort of alive, I think. There are a small number of leaves on the tree that do not look too bad though, a few whole leaves, and some winged-petiole segments of the leaves that do not look damaged.
So I guess this is what 18 °F temperatures does to an uncovered Yuzu.

The snow quickly melted away with some heavy rains. All the snow is melted now, and the temperatures have gotten "warmer" now, better weather. (high of 54 °F today, nighttime low of 41 °F) It is very possible another snowstorm might come along though.

It's been warm in the Southeast. On the West coast however, especially in the Northwest, it has been colder than normal. A low pressure zone sucked in cold air from up north in the interior of Canada. There were 3 days in a row where the daytime temperature never rose above freezing. For comparative reference, usually if there is cold spell the temperatures will at least mostly remain slightly above freezing. We got 6 inches of snow, which is a little unusual this early in the year. Usually that much snow does not fall until late January or very early February. Many years there is no snow that actually stays on the ground.

But I do remember one year where the Southeast got that terrible polar vortex, and many people's citrus were killed, while meanwhile in the Northwest on New Years Day it was unseasonably warm and camellia bushes were in partial bloom, and there was even a rose bush that seemed to be trying to send out a new bloom. That year the trunks of the Basjoo ornamental banana plants in people's yards did not even die to the ground.

Here's a picture that was taken December 17, 2021
Keep in mind that the plant had not experienced freezing temperatures yet so far in the season at the time of this picture, which explains why the leaves look so good.



You can see that it's looking pretty healthy and has put on some size.

You might want to grow multiple seeds from the hybrid. I would expect if you grow enough of them, at least one of them should result in elimination of the unsavory poncirus taste. That is assuming that the genes behave as normal dominant/recessive pairs. I believe how gene expression works in citrus is a little more complicated.

Let B represent bad taste, and b represent lack of bad taste.
Also let C represent cold hardiness and c represent lack of cold hardiness. B is dominant over b which is recessive.

the first cross was the poncirus with the pure pomelo
BB CC x bb cc = Bb Cc

next you obtained a zygotic seed from the resulting previous hybrid
Bb Cc x Bb Cc =

these are the statistical probabilities:
BB CC
BB Cc
BB cC
BB cc
Bb CC
Bb Cc
Bb cC
Bb cc
bB CC
bB Cc
bB cC
bB cc
bb CC
bb Cc
bb cC
bb cc

only the last 4 possibilities will not have the bad poncirus taste. 4 out of 12 is a 1 in 4 probability. Out of that 1 in 4, 1 in 4 will not really have any cold hardiness. Half will have moderate cold hardiness, like the hybrid parent, and the remaining 1 out of 4 will have superior cold hardiness, better than the parent. That means there will be a 1 out of 16 chance the offspring (assuming they are all zygotic) will both lack a bad taste and also be more cold hardy than the first generation hybrid.
This is probably oversimplified, of course.

what you have now would probably be more like a Bb CC type.

I apologize for hijacking your thread if theory is not what you wanted the discussion to focus on.