The Tropical Fruit Forum

Welcome to our rabbit hole.  It is  a deep one.

Yeah, cold hardy citrus breeding is no walk in the park.

Again, one of the biggest roadblocks is high rates of nucellar seed. What probably needs to happen at some point is someone needs to make a dedicated effort to breed zygotic seed into cold hardy citrus.

To do that, you'd want to take a bunch of fully zygotic varieties like Meyer lemon, ichang papeda, one of the more cold hardy pomelos, rough Seville orange or some other zygotic sour orange, then some combination of (1) breed then with each other, using ichang papeda as your main source of cold hardiness and then screen your F2 generation for hardiness (2) cross them with the handful of zygotic poncirus hybrids (eg the SuperSour series of rootstocks) and again screen for cold hardiness in the F2 generation, (3) find out which fairly cold hardy hybrids have one fully zygotic patent, ichang lemon for example, and cross it with your zygotic varieties, then screen the F1 generation for zygotic seed, and (4) cross them or some of your good F1s and F2s with the nucellar but very hardy hybrids and varieties like 5*, Dunstan, Changsha, then backcross those F1s with your fully zygotic plants again so that hopefully you'll have some fully zygotic F2s.

Lots of options, but none of them would get you results in a single generation. You'd probably need another two generations to then select for the best cold hardiness. That's at least a lifetime of breeding work. However, were someone to do this, it would make cold hardy citrus breeding much, much easier. And if you went for an four options, and were sure to include a wide variety of sources of zygotic seed (lemon, pomelos, sour orange) you'd end up with a lot of genetic diversity to work with to get the fruit quality you'd need for something not just edible, but good.

8B is probably one of the better zones for attempting a project like this.


  Nothing against what was said above, if you want that much genetic variation in your population.  But there are already 4 mostly zygotic mandarin x Ponciris hybrids in use.  US 1279, 1281 and 1282 are more than 95% zygotic, and 852 is about 85% zygotic.  And Kumin has some F2 citranges that have survived 4 (or is it 5 now?)zone 6 winters.  And he has collected some citrimelos and such to bring into his population.  I think he is closer to success and will have an easier time than is being talked of here.
I am trying about the same way but I'm way behind him, in spite of his sharing his stock with me.  We are both in zone 6, but our climate and soil are different, and our time and space are different.
Also I am also working toward a hardy finger lime.  I didn't know that Australian citrus don't cross well with Ponciris.  However, at least one finger lime x Ponciris exists in Florida.  They aren't sharing it.  At least not with me.
I hope my saying this keeps others from trying to breed hardier citrus, and trying different methods, and working toward different goal.  I have been in touch with someone in Tennessee zone 7,  working on hardier kumquats via kumquat x Ponciris.  I think he will be successful in a few generations.
I wish success to all of us.  And have fun!

There are enough branches I can try several ways.  So I'll try rooting cuttings too.

There is already a couple of threads on grafting additional rootstocks on a tree to help it grow faster and/or better.  One is "Multiple rootstock grafting" on a non-citrus.  I think there was one on citrus but I couldn't find it.  So I'm starting a new thread because I need advice.
A year ago I bought an Etrog from Logees and got a nice healthy tree but in a tiny pot.  I potted it up but it quickly declined and died.  I think it didn't have enough roots to absorb enough water in the hot dry windy climate here in central Kansas.
So I decided to buy another and graft on 2 more rootstocks.
The Etrog is about 35 cm tall and in a pot about 5 cm square and 5 cm deep.  The rootstocks I have are Citrus x Ponciris but I don't know which variety.  They are a little smaller than the Etrog.
My plan is to plant all 3 in a 3 gallon pot and use approach grafts to join them and cut off the tops of the 2 new rootstocks after the grafts have taken. 
One problem I see is keeping the Etrog alive until until the grafts take.  Another problem is that it is up to 100 F just now and this is a bad time to do all this.
Any advice is welcome.

With grapes pollen it needs dried out and stored in a freezer to last a year. Even then it's not as good as fresh and after a year goes down to barely viable at all. Fridge helps some. Room temperature won't stay viable for too long. Maybe a few months.

What about sun dragon? 1/8 poncirus and good fruit without off flavors.

So its hybrids would get 1/16 Pt from it.  Not a lot but if mated with the right other parent could give something interesting.  Not every cross has to be aimed towaed my zone 6.  You folks in zones 7 and 8 could use more diversity in your citrus groves.

I'll try it,  I had to google Banpeiyu  to find out what it is,  Not many buds left  But if pollen doesn't get here in time for these flowers, I'll freeze it for later.

My finger lime just opened several flowers this afternoon.  I had not even noticed it had buds.  So I'd like to pollinate it with P. trifoliata or its hybrids.  Second choice would be seedless Kishu.  Third choice would be any of the hardier citrus.  Would pay for your time getting the pollen and mailing, either in money or a share of the seeds, if any seeds come of it.

Today Citrus Industry news says 50 to 100 ppm improves citrus health including disease resistance and cold tolerance.
It also said several products have come out with silicon at those strengths.  Also said several products already had silicon in them but lumped silicon in "inert ingredients".  Names of such products weren't mentioned,

I just posted a couple of posts on another thread that could have been posted here.
https://tropicalfruitforum.com/index.php?topic=50899.0;topicseen
Most of you on this thread probably know everthing I put on those posts so I put it there where there were some with less background although some are on both threads and giving good advice.

Pagnr gave a lot of useful information.  I want to add a bit more.
He gave an example of a triploid hybrid with A, B, and C sets of chromosomes.  And he treated them as if each set stayed together.  In fact each set has 9 chromosomes  A1, A2, A3, etc.  B1, B2, B3, etc.  and the same for set C.
A1, B1, and C1 chromosomes are similar having evolved from an origional ancester X with chromosomes X1, X2, X3, etc.
A1, B1, and C1 are still enough alike that one can replace another and still be viable.  But they will be different enough that some, about 1/9, of the traits, will be from the the species that donated that chromosome.  So any pollen grain should have a 1, 2, 3, 4, 5, 6, 7. 8, and 9 but not always from the same species.  One might be A1 B2 C3 A4, B5 C6, A7, A8, B9. o any other combination having one chromosome of each number.  A few of the combinations might not be able to survive, but most will.  A few will be what you had hoped for, or at least a step in the direction.  Most are rejects.

Now another complicacation.  A1, B1, and C1 chromosomes don't stay as they were when you started.  During the formation of pollen and egg cells crossover happen.  I don't know how often they happen in citrus but the crops I have worked usually have about 2 per chromosome per generation.

chromosome from one species has genes
ABCDEFGHIJKL

chromosome from a different species has genes
abcdefghijkl

after a crossover you have
ABCDefghIJKL
abcdEFGHijkl

This exchange usually happens on each chromosome pair per generation, in a different location each time.  So the deck slowly gets shuffled/

Good luck!  Sounds like a good cross.

I commented some time ago that an F1 hybrid of finger lime x Ponciris+ might have a market.  I've been thinking more about it lately.