F2 citrange winter hardiness trial

[Jibro]

(Of course, you will actually have to grow the seedling until it becomes big enough to fruit, to determine that)

And that is problem, even if I get only 10 fruits from crosspolination, it's about 300 seeds with no way to select hybrids from nucellar clones (if you cross poncirus x poncirus) until they start fruiting and it took 8-10 years in my zone 6....with high probability one extreme winter, which may kill even older poncirus.

Very interesting post, jibro. Do you do Citrus breeding? If so, have you developed any selections?

I have no "big plans" for citrus breedings, I just collected more edible poncirus clones and I want to test them all in the same conditions to determine if they really have better taste...

I may try some crosses with orange or mandarine varieties, because I am curious if these "more edible" poncirus clones can create F1 poncirus hybrids with better tasting fruits than existing citrumelo and citrange...
This year i tried pollinated my fruiting poncirus with Ponderosa pollen because I am curious if some of them may produce hybrids as mother and I also have one fruit from more edible FD pollinated with Citrumelo 5*.
My biggest "success" so far is one very dwarf Flying Dragon seedling from 2017, it had first 3 flowers this spring and it has more flower buds again, so it looks like I found another precocious clone...

[kumin]

 Current photos of recent outdoor high grafts on Poncirus, as well as grafts on 1 year Poncirus.

Photos of the interior of the cold frame housing 1 1/2 year old grafted clones of the original survivors & 2 1/2 year old original surviving seedlings.




Recent outdoor high grafts of TaiTri, 5* citrumelo, and various Conestoga selections.


A few of 440 recent grafts on Poncirus year old seedlings. There are 8 seedlings per pot.


Conestoga #001 high graft on Poncirus needs support due to very rapid slender growth.
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More recent outdoor grafts on fruiting age Poncirus.
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2nd year graft of Conestoga #011 on fruiting age Poncirus, hopefully it'll flower in 2-3 years.

[vnomonee]

I have no "big plans" for citrus breedings, I just collected more edible poncirus clones and I want to test them all in the same conditions to determine if they really have better taste...

Are there any large scale citrus breeding programs using Poncirus+ (reduced/without bitterness) to recreate/improve all of the "bad tasting" hybrids that already exist?

[kumin]

I'm not aware of many Poncirus+ trees in the US, especially in regards to mature, fruiting trees. This should not be a major obstacle, as well grown Poncirus fruits rather young. I've been in the process of grafting juvenile phase Poncirus+ on year old seedlings, I'm uncertain as to the success rate, but I should know shortly.

Answering your question a bit more directly, this would be a great project for someone with a collection of various zygotic cultivars, used as maternal, or paternal parents. Walt has suggested doing exactly what you're proposing.

I would love to see young people getting involved with cold hardy Citrus breeding. Realistically, some of us have collected, selected, or created selections that while not reaching all of the goals we're seeking, may provide valuable breeding material for further advances.

[kumin]

This is Conestoga A-26 the tallest specimen at 28 months of age. Knowing it was at least 8' (2,43M) tall, I measured it and found it to be 108" (2,74M) tall. The node count is just over 100 nodes. Due to it's very rapid growth it will likely still be several years until flowering. This tree strongly resembles Poncirus, with leaves smaller than Poncirus. The growth is extremely upright. The cold frame is 11' (3.35M) tall and will probably be too low by next autumn.

[kumin]

Top grafts on Poncirus after 15 months.






Top grafts on Poncirus after 2-3 months.




The 15 months old scions have gone through a mild Winter without damage. There are approximately 20 scions to be exposed during the upcoming winter.

[mikkel]

It is really impressive how fast they grow. Have you ever thought of using paclobutrazol to trigger flowering?
Ilya has done some research on this.

[kumin]

Mikkel, our Summers on the East Coast are characterized by hot, humid weather with fairly long days. Your days are obviously longer during Summer. Our Summers can come to an abrupt end, which can leave tender, vulnerable growth  going into Winter. I have been pleasantly surprised by the growth rate of the Citrus in my project.
I've skimmed through methods to hasten flowering/fruiting, but feel that a bit more scaffolding development would be beneficial before utilizing those techniques.

[kumin]

This may be rather optimistic, but several potential flower buds have developed on Conestoga 011 top grafts on Poncirus. These scions will only be 3 years old from seed by April 2021. They clearly appear different from the majority of the vegetative buds. Perhaps they are simply imperfect male flowers on the scion's first bloom.

If these are not flower buds, I suspect they are precursors to flowering in 1-2 years.

Vegetative bud.


These could potentially be flower buds.

[hardyvermont]

Last picture looks tetraploid.   

[kumin]

The photos are all from the same clone including the first one. The potential tetraploidy has previously been suggested. If tetraploid, the larger buds may be caused by tetraploidy rather than flower initiation.

[hardyvermont]

I have some F1 citrus x poncirus hybrids, within each plant there are varying leaf shape and thickness.  Perhaps varying amounts of tetraploid cells may be present in different branches of the plants.   This is apparent only when poncirus is part of the cross.

[kumin]

Recent photos:

5* citrumelo - very vigorous and 8 ft. (2.43 meters) tall - 18 months from seed



Original test plot - 100's of survivors 30 months from seed most are unlikely to survive above frozen soil in the upcoming Winter.



Monofoliate Conestoga #058 30 months from seed.



Conestoga # 002 deciduous - The original plant is 30 months old from seed, very low thorniness. This is a 16 month old  plant grafted on Poncirus.



Conestoga A-026 deciduous 10' ( 3 meters) tall 30 months from seed.



Various Conestoga seedlings 30 months from seed.



Ichangequat 6-7-2 18 months from seed suffered freeze damage and Botrytis infection during the past Winter.



Poncirus + entering autumn color change 18 months from seed

[Ilya11]

You have excellent  growing conditions.

[kumin]

Various degrees of deciduous behavior among Poncirus and hybrids:

Soil grown Poncirus seedlings. Leaves are turning yellow, but few have been dropped.


Poncirus in containers has dropped more of it's leaves.


Hybrids in cold frame, with varying degrees of color change: TaiTri and F2 segentranges.


Tallest trees in the far left are Poncirus+ more distant tall trees on the left are 5* citrumelo. the remainder of the trees are F2 segentranges.

[kumin]

An update on the status of the hybrids I have at present:
 The ranking in regards to cold hardiness is very consistent from year to year. It's likely the hardiest trees are genetically very close to Poncirus. Hopefully there will be some Citrus traits expressed at time of flowering/fruiting in a few years. I see little or no difference to this point, in regards to cold hardiness, between Conestoga # 010,#011, and Poncirus.

In addition to the hybrids I am also comparing Poncirus+ and Poncirus in regards to cold hardiness. To this point, I haven't noticed less hardiness in Poncirus+.

The low temperature to date has been +10 deg. F. (-12 deg. C)

The trees in the cold frame are exposed to the same low temperatures, but have higher daily highs on sunny days. The most noticeable difference is that there's no desiccation inside the cold frame, unlike the evergreen grafts exposed to the outdoors.

TaiTri outdoor graft on Poncirus, shows no deciduousness - however, TaiTri in cold frame has dropped +/- 25% of leaves.


5* Citrumelo shows no leaf drop outdoors, nor in cold frame. The twigs don't show too much damage, perhaps a bit of desiccation.


Conestoga 058 segentrange in poor condition, strongly evergreen, most Citrus-like of all my hybrids, also the least cold hardy



Conestoga 001 segentrange partially deciduous appears relatively cold hardy.


Conestoga 010 segentrange, fully deciduous and second hardiest specimen.


Conestoga 011 segenrange, fully deciduous, hardiest specimen of my hybrids.

[tedburn]

Hello Kumin, wish you a very good and healthy 2021 and further very good progress and success in your ambitioned breeding program.
I always like to read your interesting reports and view your pics.Best regards Frank 👍

[Ilya11]

Kumin, I wonder if you kept some nucellar seedlings in cold frame  as a control? What is their resistance?

[kumin]

Ilya, that's a very good question. In the Winter of 2018/2019 most of the seedlings were killed to the soil level. During the Summer of 2019 several hundred roots sprouted shoots that grew until the Winter of 2019/2020, which saw low temperatures of -12 C (+10 F). Some are clearly zygotic, others have considerable uniformity. The present Winter low temperature has again been -12 C (+10 F) . The trees that survived last Winter's low temperature didn't make new growth until June. These trees show little damage to this point.

The trees in the cold frame show both more damage, as well as less damage than the outdoor trees. The outdoor trees show more desiccation, the cold frame trees have hardened off less, allowing the stems to be more succulent.

In regards to your question concerning C-35 trees in the cold frame, there are 2 trees I believe to be C-35 hitchhikers on F2 roots by means of root grafting. They have larger diameter straight stems. I am attaching  photos of outdoor survivors with minimal damage as will as 1 of the likely C-35 trees in the cold frame.


Outdoor survivors -  original plot



Original trial plot



Original plot



A very likely C-35 tree in the cold frame. These trees have thicker, straighter trunks than the F2 trees.


The question of C-35 cold hardiness has been raised several times. My results have been that C-35 has considerable cold hardiness provided it has an opportunity to develop cold resistance over a long period. I suspect that suddenly going from warm temperatures (allowing active growth),to cold temperatures, results in much less satisfactory results.

[poncirsguy]

My C35 was outside in winter and took a lot of damage at 10F after over 2 months with no warm weather.

[kumin]

Poncirusguy, although my suspected C-35 trees survived the past Winter as well as this Winter to this point, their growth was delayed in the Spring. The 2 trees in the cold frame are triple the size of the outdoor trees.
Additionally, severe cold would almost certainly kill them to soil level. We have had minimal frozen soil since 2019. Our area is capable of frost depth of 36". Not only would C-35 tops be doomed, the roots might also be.
My focus is on the hardier F2 trees, a few of which might servive subzero F. temperatures.

[kumin]

Midwinter photos of cold frame hybrids and one outdoor hybrid:

A heavier caliper Citrange seedling, nearing 3 years of age.


One of the largest Citrange seedlings, nearing 3 years of age


Monofoliate Conestoga #58 grafted on Poncirus, 16 months post grafting.


5* Citrumelo seedling.


Grafted Conestoga F2 monofoliate Citrange, 16 months post grafting.


Vigorous 5* Citrumelo seedling.


Original Conestoga #058 tree, nearing 3 years of age. Most Citrus-like of all my seedlings, also the least hardy.
#058 has the longest spines of all my trees. They are quite slender, though, unlike the stout Poncirus spines.


Out of doors Conestoga # 001, not fully deciduous, slightly less hardy than Conestoga # 11 and #10. Hardier than 5* Citrumelo, or TaiTri. This tree is 10' tall.

[Ilya11]

Kumin,
What were the lows inside this frame?

[kumin]

Ilya, the lows are the same as outside. To this point the lows have been 10° F  (-12C). The cold frame gets at least 10-15°C warmer than outside during sunny days. On cloudy, windy days there is less temperature rise.

The greatest benefit is wind protection and daytime amelioration of cold temperatures. A downside is that the stem tissues remain a bit more succulent, which in the case of severe cold temperatures could worsen bark destruction by freezing.

[Perplexed]

Kumin, I noticed that with 5* the leaves are always curly/wavy. That's the same for me, mine also have the same leaf pattern.