F2 citrange winter hardiness trial

[kumin]

Perplexed, all my 5* seedlings show the same wavy pattern. How old are your trees? Are your trees also seedlings?

[kumin]

   At this point I'm contemplating a focus on creating crosses between the hardiest F2 Citrange survivors from the 2018/2019 Winter cold hardy trials and Changsha X Poncirus hybrids such as 852 Citrandarin and closely related selections. This would bring additional Citrus genetics into the "bloodline" while compromising little in the way of hardiness.

   Several downsides to the F2 Citrange selections are:

1. Poncirus off-flavors tend to be more pronounced in Citranges than Citrandarins.

2. Sweet Orange parentage leans toward longer periods of juvenility than Mandarin parentage.

3. At this stage the F2 Citrange selections appear to approach Poncirus in hardiness, but are likely to retain off-flavors and perhaps poor coloring. The three characteristics in their favor are hardiness, deciduousness, and at least some Citrus genes.

Benefits of using Changsha X Poncirus parentage in crosses.

1. Changsha Mandarins are more cold hardy than Sweet Oranges.

2. Adding Citrange X Citrandarin parentage should promote a more diverse genetic base.

3. Changsha Mandarins are highly colored, sweet, prolific fruit and seed bearers.

4. Changsha seediness is of little concern at this stage and is actually desirable for efficient seed production.

5. Using zygotic seed parents would streamline efficiencies by not wasting resources on nucellar seedlings.

6. If these breeding plans succeed, I hope to do new severe, cold hardiness test trials.

[Perplexed]

Perplexed, all my 5* seedlings show the same wavy pattern. How old are your trees? Are your trees also seedlings?

Mine are about a year old in a pot. Still very young but is very cold hardy.

[mikkel]

   At this point...

just ideas:
It would be interesting to backcross it to the orange parent,  maybe as a side project beside your plans.
You could take HRS899A into your consideration too. It is an F2 Changsha x P.t. hybrid quite hardy and has good fruits as far as I heard about.

[Till]

The curvy leaves of Swingle 5 Star are probably a sign of dehydration because roots could not provide enough water. My Sanford Curafora and US199 have also curvy leaves during winter and thereafter. It has nothing to do with frostbite as such leaves remain vital for a very long time.

[Till]

Kumin, I am looking forward how your plans succeed. I would also try to cross your hardy seedling with Poncirus hybrids. When you have the potential for mass selection then use it. Crossing with citrus would compromize hardiness too much I think. But edible Changsha hybrids, as Mikkel suggest, seems to be reasonable, too, although I fear that would also weaken hardiness. Depends on how many generations you plan. At your growing conditions, 3 generations seem to be reasonable.

[kumin]

Till, I presently have no plans of crossing back to pure Citrus due to loss of hardiness and number of years required to recover the required hardiness. The paths I'm interested in are crossing to edible Citrandarins, allowing the selections to self-pollinate, and crossing with Poncirus+ to maintain the greatest hardiness.
Additionally, the sooner the zygotic/nucellar status can be determined among the F2 selections, the better.

[mikkel]

I don't think backcrossing would lead to lower winter hardiness in every case, certainly in most cases, but in exceptions there might be a chance. Hardiness is not only controlled by one gene, but backcrossing could also work with several genes. It just has lower chances... but it has higher chances of sorting out the right genes than mixing them with other sources.... at least in theory...
In practice I would go both directions...

[Ilya11]

This is a matter of numbers.
From my experience if you are able to raise ~200  zygotes from a backcross of F1 plant , there is at least a dozen that are as hardy as an original F1.

[kumin]

The curvy leaves of Swingle 5 Star are probably a sign of dehydration because roots could not provide enough water. My Sanford Curafora and US199 have also curvy leaves during winter and thereafter. It has nothing to do with frostbite as such leaves remain vital for a very long time.

The curving leaves on 5* are most likely genetic in origin, as this characteristic is especially prominent is vigorous upright growth, even during Summertime. I haven't seen it relating to stress, as I'm able to distinguish 5* seedlings from all the other trees by this characteristic.

Ilya may be able to weigh in on his experiences with 5* leaf characteristics.

[Ilya11]

In a summer they are only slightly curvy, while as of today , after  a night at -9.5C they are almost tubular.
I guess this is a sign of cold hardiness adaptation connected with  ability to diminish the surface of water loss.Grapefruit and orange leaves  are not showing this and stay flat until the lethal damage.

[kumin]

 Feb 26 2021 branch condition comparison between TaiTri citradia, 5* citrumelo, and Conestoga 011 citrange.

TaiTri shows the most damage, with pitting of the bark surface. Unexpectedly, it hasn't shed its leaves. Not certain if this graft will survive the Winter at this point.


5* citrumelo leaves are mostly dead, however the bark surface appears to be in better condition than TaiTri and may be viable. Less bark surface pitting on this Citrumelo.


Conestoga 011 F2 citrange has good color and shows no ill effects from the Winter to this point. This tree is fully deciduous.



This Winter has been mild, with a few lows of 10 degrees F (-12 deg C). It has not been a serious cold test and forecasts don't indicate any in the remaining Winter.

After a night of rain the appearances are quite different.
 
This is an unidentified F2 citrange, with hardiness equal to, or slightly greater than 5* citrumelo.


5* citrumelo after a night of rain. The appearance is much better.



TaiTri on Feb 27 after a night of rain. The stem is a bit better looking than it was yesterday.

[Ilya11]

5star is exceptionally resistant to the bark damage.

[kumin]

Ilya, I'm surprised to see portions of the leaves still alive at this point. Have you encountered any deciduous 5* progeny in your breeding efforts? 5* does quite well for not being deciduous, but a deciduous version might be even better.

I'm surprised the outdoor TiaTri isn't dropping it's leaves, but the cold frame trees are partially dropping theirs.

[Ilya11]

Do not have much experience with its open pollinated seedlings, but in crosses occasionally there are  some deciduous plants.

[kumin]

Due to having 2 consecutive mild Winters there are still surviving plants in the original test plot. There's a newly discovered 3 year old deciduous seedling among less hardy plants. This seedling shows no cold damage, after a mild, but long Winter. I really should take a closer look at the remaining plants to determine if there are more surprises.

[kumin]

Recent warm weather is driving some bud swelling on Poncirus, as well as some of the hybrids. Lows of 26 and 29 deg.F are predicted by end of week. Should not be a major problem, but is a bit of a concern after highs near 80 deg.F last week.

2 horizontal TaiTri twigs, appear to survive, a bit less resistant than 5* Citrumelo. Have dropped their leaves recently.



5* Citrumelo (Light green stems)has dropped all leaves and shows little Winter stem damage


Poncirus+ twigs show no Winter damage.

[kumin]

Conestoga 001 high grafted on Poncirus has wintered well and has bud break within 2" (5 CM) of the apical tip. This selection is not the very hardiest, but is likely about the 6th hardiest. It ranks hardier than TaiTri and 5* Citrumelo.

The tip of this graft is nearly 10'  (3.3 meters approximately) high from the ground.

This shoot made rapid growth last Summer and continued to do so into Autumn.



Conestoga 001 after the initial Winter hardy trial.

[kumin]

TaiTri post Winter recovery.


segentrange # 011 showed no Winter damage.


Segentrange #058 graft, barely survived Winter, most Citrus-like in appearance.



An additional #011 Segentrange, no Winter damage.


Segentrange showing poor Winter hardiness.


Outdoor 5* Citrumelo showing complete recovery after Winter.

[Ilya11]

Have Taitri and 5star shown the same degree of recovery this season?

[kumin]

Yes, Ilya, their hardiness in my location was nearly identical. The surprise for me was that the TaiTri out of doors showed no deciduous behavior. The trees in the unheated cold frame were partially deciduous. 5* showed no deciduous behavior until new Spring growth flushed out of doors. The cold frame 5* still retain last year's foliage.

TaiTri and 5* are more hardy than my most tender Segentranges and less hardy than the hardiest segentranges.

[mikkel]

For me TaiTri seedlings were more hardy than some 5Star seedlings this winter. Both were under a snow cover.

[Zitrusgaertner]

TaiTri and 5* are more hardy than the most tender Segentranges and less hardy than the hardiest segentranges.
[/quote]

Kumin, what are the hardiest Segentranges?

Of my garden-citri Ichangensis IVIA from seed, Citrumelo 5*, Citsuma Prague and Citrandarin US812 (from seed) are about equal in hardiness. Yuzu3 survived the last winter without any dieback or even loss of foliage. Citrange Morton (on Swingle Citrumelo) and some yuzu from Bernhard Voss died. Most likely my fault caused by wrong protection which allowed the winter sun to heat up the shelter and broke dormancy. Morton was not well established and Swingle might not be the right rootstock. Tmin was -10 to -12°. Not really low in fact.

[kumin]

Zitrusgaertner, the segentranges I refer to are the selections that survived the Winter cold hardy trial in 2018/2019. Out of ~20 000 seedlings several dozen survived in varied condition. I subsequently named the more remarkable selections "Conestoga" series and assigned individual numbers to them.

Conestoga 011 and 010 are the very hardiest, with about 8 more close in cold hardiness. Several of the most Citrus-like phenotypes were also kept and propagated, these are less hardy than 5* and TaiTri. Conestoga #010 and #011 approach Poncirus in hardiness.

None of the selections are mature enough to fruit. The hardiest selections have a rather Poncirus like appearance and may also exhibit similar off flavors.

Coldest temperature during trial, January 2019



~20 000 seedlings April 2018



Segentrange survivor among many dead seedlings.


3 year old survivor in the original trial row, never protected.

[Zitrusgaertner]

Very interesting. Did you apply any sun protection? My opinion is, that more citri are killed by sun than by frost alone. They are all on own roots by now, are they? Du you plan to craft some on PT?