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Author Topic: F2 citrange winter hardiness trial  (Read 1013 times)

kumin

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F2 citrange winter hardiness trial
« on: January 25, 2019, 08:04:22 AM »
I'm trialing a population of F2 Citrange seedlings this winter in zone 6b in SE PA. There is considerable variability in the resistance to low temperatures, with some dying in November and others still viable at this point. The population is a mixture of nucellar  F1 and zygotic F2 seedlings. The F1 are freezing out at present, but a number of the F2 are surpassing the F1 in hardiness and a few appear to be surviving the winter. My hope that several will approach the hardiness of P. trifoliata.

Any survivors would then be evaluated for palatability. My focus is centered on hardiness, with palatability being secondary.

I've grown poncirus since 1980 and lost everything above the snowdrifts in Jan of 1994. This was after 2 consecutive nights at -24 F. The trees resprouted below the snow height and haven't been injured since.

hardyvermont

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Re: F2 citrange winter hardiness trial
« Reply #1 on: January 25, 2019, 01:10:14 PM »

I've grown poncirus since 1980 and lost everything above the snowdrifts in Jan of 1994. This was after 2 consecutive nights at -24 F. The trees resprouted below the snow height and haven't been injured since.

kumin, Thanks for this information.  Where are you growing poncirus?  Full sun, partial shade, protected from the wind?  Have you noticed any difference between poncirus plants? 

kumin

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Re: F2 citrange winter hardiness trial
« Reply #2 on: January 25, 2019, 01:42:38 PM »
hardyvermont, I have Poncirus plantings at three locations on the same property. All are in clay soil, one location  is well drained , the remaining two are poorly drained. The trees growing in full sun have the the most vigor. Last winter I removed a M. Grandiflora tree that was shading the largest Poncirus tree and upon release the Poncirus  tree responded positively. Most of my trees are fairly close to buildings which could block or concentrate the wind. I haven't recently germinated  Poncirus seedlings on large scale. When I did in the past, I saw the occasional seedling I suspected of being tetraploid. Due to generally having rather high % of nucellar (clonal copies) seedlings, one usually sees a lot of uniformity.

The citranges by contrast have no wind protection other than the density at which they're planted. They are planted at about 20 seedlings per sq. ft.

kumin

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Re: F2 citrange winter hardiness trial
« Reply #3 on: January 25, 2019, 01:58:21 PM »
hardyvermont, I lost a planting of first year Poncirus a few decades ago by planting them into loosely cultivated soil and not allowing the soil to solidify during the growing season. During the winter 500-600 succumbed to late winter frost heave. In early April I could very easily pull the dead trees out by hand. They were approximately a foot tall at that time. There were no survivors. Mulching the soil might have saved them all.

Walt

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Re: F2 citrange winter hardiness trial
« Reply #4 on: January 25, 2019, 03:04:53 PM »
What  is your source of citrange seeds?
I'm glad to know someone else in the USA is growing F2 citrus x trifoliate hybrids. But mine are still at the tiny seedling stage, certainly not ready to face zone 6 winter.  In fact,  I assume I'll need at least one backcross to trifoliate, maybe two.  I would love it if you proved me wrong.
Keep us up to date on your results

kumin

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Re: F2 citrange winter hardiness trial
« Reply #5 on: January 25, 2019, 07:53:36 PM »
Walt, being of similar age you, I am using brute force (large populations) in an attempt to increase to odds of obtaining very hardy F2 segentranges in a short time span. After planting a number of putative " cold hardy " cultivars that failed, I am seeking plants with nearly the full hardiness of Poncirus.  I began with an initial population of 20,000+ seedlings. The seedlings are 85% nucellar and 15% zygotic, so the effective population under trial  is 3,000 plants.

The seeds were germinated in April of 2018 and planted outdoors in June, 2018. These plants are not protected against the cold in any way. Survivors, if any will be protected going forward, knowing they have the necessary genetics. At this point the population will be very small and easier to protect.

Googling  "citrus tree seed California" will give you 2 hits that sell seed by liter or quart. If you need details on how to germinate large quantities of Citrus seed I can't make a recommendation, but I can tell you how I did mine.






Florian

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Re: F2 citrange winter hardiness trial
« Reply #6 on: January 26, 2019, 04:45:45 AM »
Check out the Hamlin x FD: http://tropicalfruitforum.com/index.php?topic=28270.msg321750#msg321750.
It appears to be rather coldhardy.

Walt

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Re: F2 citrange winter hardiness trial
« Reply #7 on: January 26, 2019, 02:33:55 PM »
Kumin
3,000 is a number I can respect.  I stated in long term cold hardy thread why I think F2 citranges will be less cold hardy than than F1.  But 3,000 trys?  If I'm wrong about even one of them, you win.  This is a real effort.
I think your chances would be better with older trees.  But you are doing a big job, so do it your way and I hope you succeed.
Thanks for the information about seed source.

Ilya11

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Re: F2 citrange winter hardiness trial
« Reply #8 on: January 26, 2019, 02:48:24 PM »
HamlinxFD is certainly not hardy in zone 6.

I wonder if citrandarins like US852 are  better choice for such large scale testings. I guess 5-10 mother plants will give sufficient quantities of starting seeds.

For the germination, from my experience, the best method is perlite/buggy approach used for palm seeds.
Seeds are germinated in zip locked plastic bag in moist, but not wet perlite at 25C. After germination seedlings can be transplanted in common pots to grow under artificial light and transplanted in  spring in the open ground.
I am germinating each season around thousand of seeds  by this method (my record is 3000), selection to discard nucellar seedlings  and plants with poncirus aftertaste in leaves can be done very early, before open ground planting.
« Last Edit: January 26, 2019, 02:50:20 PM by Ilya11 »
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SoCal2warm

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Re: F2 citrange winter hardiness trial
« Reply #9 on: January 26, 2019, 02:56:35 PM »
I wonder if citrandarins like US852 are  better choice for such large scale testings. I guess 5-10 mother plants will give sufficient quantities of starting seeds.
I just looked at my germinating US852 seeds. Four of them had begun sprouting, and of those 2 of them were polyembryonic and 2 only had single sprouts.

kumin

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Re: F2 citrange winter hardiness trial
« Reply #10 on: January 26, 2019, 02:59:03 PM »
3,000 is a little less impressive than it sounds, approximately half are genetically dwarf which is not unusual for F2 zygotic citranges. Many them are too lacking in vigor to hold much promise. Long story short- I did a status survey today and believe 100 to 150 plants are relatively unscathed, but February can be brutal to plants. Some winter cold damage is accumulative, as any individual cold event can be. The best looking plants phenotypically favor Poncirus rather strongly. However, they are not identical to one another in appearance. Hopefully they will carry some Citrus genes.

kumin

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Re: F2 citrange winter hardiness trial
« Reply #11 on: January 26, 2019, 04:32:51 PM »
The germination technique I used, was placing the seeds in mesh bags, then using a repurposed dishwasher with thermostat control of water temperature, aerated/soaked them for 24 hours at 86 degrees F. I then removed them and stratified the seed coat for 30 minutes, followed by neutralizing the solution and rinsing them thoroughly. They were then returned to another 24 hrs of soaking, followed by planting immediately into a germination bed, again at 86 degrees F. They were planted 1.8 - 2 millimeters deep. Areas cooler than 86 degrees had a bit of seed decay. Seeds planted too shallow lifted out of the soil. Seeds planted too deep had delayed emergence. Emergence began at 7 days and continued a little over a week.

The water used in the soak was slightly chlorinated to prevent decay. The water was drained and replaced every 6 hours. As the seedlings grew larger and May weather became warmer the bed temperature was dropped to 75 deg. F. The seedlings were field planted on June 12, 2018. By end of September the tallest seedlings were 48" tall. The average was closer to 30" - 36 ' tall.

kumin

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Re: F2 citrange winter hardiness trial
« Reply #12 on: January 26, 2019, 06:42:50 PM »
Ilya 11 Thanks for your suggestion of a leaf taste test. During field planting I noticed some plants were pleasantly sweetly aromatic, but I didn't trust that there was a definitive correlation between plant sap taste and fruit taste. Relying on such a test could dramatically reduce the time, labor, space, etc. required to plant seedlings.

SoCal2warm

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Re: F2 citrange winter hardiness trial
« Reply #13 on: January 27, 2019, 01:18:28 AM »
I wonder if citrandarins like US852 are  better choice for such large scale testings. I guess 5-10 mother plants will give sufficient quantities of starting seeds.
Yes, US 852 is a hybrid between Changsha mandarin (already pretty hardy) and trifoliate, and can survive well into zone 7.

Apparently their flavor isn't too terrible. There's a video where one guy is managing to enjoy eating them.

Walt

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Re: F2 citrange winter hardiness trial
« Reply #14 on: January 27, 2019, 01:35:39 AM »
I've been away from my computer a few hours, but this hasn't been out of my mind.  Kumin. your results so far alreadyshow  that I was wrong that all the F2 would be less hardy than the F1.  You said ALL your F1s are dead, but some of your F2s live.  I really didn't expect that.
You made my day.

kumin

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Re: F2 citrange winter hardiness trial
« Reply #15 on: January 27, 2019, 03:26:06 AM »
Photos taken yesterday of one plant lacking hardiness and one showing little damage.






« Last Edit: January 27, 2019, 03:48:07 AM by kumin »

Ilya11

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Re: F2 citrange winter hardiness trial
« Reply #16 on: January 27, 2019, 03:54:43 AM »
I then removed them and stratified the seed coat for 30 minutes, followed by neutralizing the solution and rinsing them thoroughly.
Kumin,
I do not understand what do you mean by stratification? Certainly not cold treatment, may be washing soda incubation?
Your brute force approach is very impressive, hopefully it will produce some hybrids as resistant as poncirus. Still, most of the freeze damage occurs in spring when small stem cracks begin to be infected.
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                       Ilya

kumin

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Re: F2 citrange winter hardiness trial
« Reply #17 on: January 27, 2019, 04:56:13 AM »
Ilya11, Yes, it was a strictly controlled alkali treatment followed by water flushing, again followed by weak acid rinse. then flushed repeatedly. At this point the final 24 hour soak was begun. I've just noticed I referred to the process as "stratification" my intent was to say "scarification".
« Last Edit: January 27, 2019, 05:02:35 AM by kumin »

mikkel

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Re: F2 citrange winter hardiness trial
« Reply #18 on: January 27, 2019, 05:19:14 AM »
kumin, you are doing impressive work!
Just a notification there is a Citrandarin F2 (but it could be F3 too) in Germany fully hardy and very similiar to Poncirus but not zone 6 more like zone 7.
It is a HRS 899 (or offspring of it) but unknown which one. There are (or were) HRS 899 a to k . All HRS 899 are offspring of US852 or another hybrid with Changsha x Poncirus parentage.


on the left HRS 899 to the right Poncirus

« Last Edit: January 27, 2019, 05:20:45 AM by mikkel »

kumin

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Re: F2 citrange winter hardiness trial
« Reply #19 on: January 27, 2019, 05:38:31 AM »
Thanks, Mikkel the reversal of the hybrid retaining the fruit while dropping the leaves is interesting. One aspect of Poncirus fruit is the rapid dropping of the fruit followed by short storage life. I have no experience with the variability of Poncirus hybrids fruit storage life.

usirius

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Re: F2 citrange winter hardiness trial
« Reply #20 on: January 27, 2019, 02:42:50 PM »
@Mikkel I can confirm your observation. Fruits of HRS89 (Poncirus x Changsa F2) stay much longer on the tree than the fruits of Poncirus trifoliata. See also my other post with photo here: http://tropicalfruitforum.com/index.php?topic=30863.0
« Last Edit: January 28, 2019, 03:15:09 AM by usirius »
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mikkel

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Re: F2 citrange winter hardiness trial
« Reply #21 on: January 27, 2019, 06:02:12 PM »
@usirius
I have the feeling this picture might be yours? Is it?

usirius

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Re: F2 citrange winter hardiness trial
« Reply #22 on: January 28, 2019, 03:16:15 AM »
Yes mikkel, the picture above including the text has been done by myself some years ago ;-)
„May your choices reflect your hopes, not your fears.“ N. Mandela

mikkel

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Re: F2 citrange winter hardiness trial
« Reply #23 on: January 28, 2019, 05:43:43 AM »
I knew it :) We had some contact then.
Shall I put your name under the picture?
Is this 899 above the same as the pear shaped one you posted in the other thread?

usirius

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Re: F2 citrange winter hardiness trial
« Reply #24 on: January 28, 2019, 05:59:04 AM »
Concerning the picture all is okay! On the first view I think it is the same HRA 899 selection. If helpful can check this in my garden to a later time. -  But which selection is it? The foliage is mostly trifoliate. Thank you also for the hint to find the description of Bernhard Voss- I catched the direct link to this descritption: https://web.archive.org/web/20130106094639fw_/http://www.agrumi-voss.de/hrs.htm    ->   This description is very old and it is related to the habitus of relatively young plants. It is possible that shape and size of foliage varies during aging. So a more actual description including fruits would be very interesting. Do you know if Bernhard Voss has done any newer documentation of the HRS899 selections - may be he published a book about those or has written something about them in an article in a garden journal?
„May your choices reflect your hopes, not your fears.“ N. Mandela

mikkel

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Re: F2 citrange winter hardiness trial
« Reply #25 on: January 28, 2019, 06:30:57 AM »
I spoke several times with him. As far as I know he has no plants left. Some years ago he gave most of his plants away. I picked what seemed to be interesting but there were only 899 J and A among the plants.
Meeder, Eugen Schleipfner and CitrusBali might have some other varieties. But it seems many have lost the letter so it is often only HRS 899.

Yes I think the mature plants might have different leaves now. In his description only O and Q are fully trifoliate .
Here you can find some results from the cold tests.

How many HRS 899 do you have?
Could you check your plant again I am very interested.

kumin

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Re: F2 citrange winter hardiness trial
« Reply #26 on: January 28, 2019, 08:08:51 AM »
Mikkel, Vielen Dank für die Winterhärteinformationen. Unter den Sorten scheint es erhebliche Unterschiede zu geben.

usirius

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Re: F2 citrange winter hardiness trial
« Reply #27 on: January 28, 2019, 02:05:28 PM »
@ Mikkel: I started with about 8 selections of HRS899. Only the selections survived after the first winter. Another selection died next winter, and for many years I had only two selections left. I'm not sure, maybe three or four years ago one of the two remaining selections died. After all these years only this one has survived and this selection is as robust in my opinion as Poncirus trifoliata. It showed no damage in all winters in the past. Even an early warm-up in the spring with subsequent freezing is no problem for this selection. This is often a big problem for most "robust" citrus hybrids and selection. The only negative feature is that the fruits are inedible - smaller and a worse taste like poncirus fruits ;-)
« Last Edit: January 28, 2019, 02:10:20 PM by usirius »
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Ilya11

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Re: F2 citrange winter hardiness trial
« Reply #28 on: January 29, 2019, 09:46:09 AM »
Kumin,
I wonder if you observed the seedlings with  tendency of autumn leaf yellowing/falling ?
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kumin

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Re: F2 citrange winter hardiness trial
« Reply #29 on: January 29, 2019, 11:59:46 AM »
Ilya11, There is considerable variation in leaf color, some are very dark green, some are showing a bronzing response to the cold. Others show a reddish tint where the leaflets join the petioles. The F1 seedlings are uniformly dark green and shriveling as they desiccate. There are a number that have a yellowish cast, but most leaves have not dropped at this point.

One thing to keep in mind is that straight Poncirus often isn't reliably deciduous until the third year. I'm attaching a photo of self seeded 2-year old pure Poncirus that have changed color somewhat, but still haven't dropped their leaves.


« Last Edit: January 29, 2019, 12:04:00 PM by kumin »

Ilya11

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Re: F2 citrange winter hardiness trial
« Reply #30 on: January 29, 2019, 12:06:52 PM »
Thank you, I am quite convinced that for the robust hardiness beyond zone7, the citrus hybrid should drop its leaves in autumn. Among my F1xcitrus seedlings such plants are extremely rare.
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kumin

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Re: F2 citrange winter hardiness trial
« Reply #31 on: January 29, 2019, 12:40:52 PM »
Ilya11, I agree with you. It's very likely that being evergreen puts too much stress and demands on the plants. There are a few plants that have dropped their leaves. I am not certain if this is from stress or preparation for winter. The trees I favor at present may not be the best in the next several months.

kumin

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Re: F2 citrange winter hardiness trial
« Reply #32 on: February 01, 2019, 01:45:57 PM »
The present low temperature event has struck the local area. Recent daytime highs are approximately +15 deg. F., today is expected to reach +20 F. Local lows have been +3 F,  -11.8 F, +2 F and tonight + 10 F. The - 11.8 F reading was considerably lower than the forecast. These midwinter temperatures aren't a problem for Poncirus. Concerning the F2 citranges, however, this is a severe test. I will survey the plants again once we get a prolonged thaw .  Survival is obviously not assured. A thaw is forecast to begin tomorrow. If any manage to survive they will be protected in subsequent winters.


« Last Edit: February 01, 2019, 03:13:21 PM by kumin »

Ilya11

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Re: F2 citrange winter hardiness trial
« Reply #33 on: February 01, 2019, 06:26:06 PM »
At least  all your C35 nucellar seedlings will be dead, C35 is probably the least hardy of all citranges.
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SoCal2warm

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Re: F2 citrange winter hardiness trial
« Reply #34 on: February 02, 2019, 12:24:02 AM »
Citranges are not as hardy as citrandarins or citrumelos because oranges are not as hardy as mandarins or the vigorous grapefruit varieties that citrumelos were bred from. (Though I don't think the difference is huge)

However, I predict we'll see a lot more hardiness manifest in the F2 generation, at least in 25 percent of the seedlings.
That's because another cross has the chance to eleminate dominant genes that may carry cold vulnerability, or manifest recessive genes that would carry cold hardiness.
When you have an F1 cross, you're pretty much guranteed that 50 percent of the genes are going to come from poncirus and 50 percent from orange, but when you take that hybrid and cross it again, even if it's with itself, there are a lot more possibilities.
You might (though exceedingly unlikely) even be able to manifest all the good genes from the edible orange parent with all the beneficial cold hardiness genes from the poncirus parent.

Ilya11

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Re: F2 citrange winter hardiness trial
« Reply #35 on: February 02, 2019, 05:18:54 AM »
Poncirus contains several gene regions responsible for its freeze resistance and its genome is highly heterozygous. That is why  F1 hybrids with citrus are showing a large variation for winter hardiness.
Three hundreds of its F1 hybrids with very frost sensitive pummelo show a wide distribution of freeze damage.

 article



Quite possible that C35 citrange inherited a rather unfavorable set of gene alleles from its poncirus parent explaining its poor winter performance.
Best regards,
                       Ilya

Millet

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Re: F2 citrange winter hardiness trial
« Reply #36 on: February 02, 2019, 02:06:25 PM »
For forum members reading through this post, that are not familiar with what the variety HRS 899 is see below:

Newly bred variety, the tests haven’t been finalized yet. It is a cross of tangerine variety 'Changsha' and Poncirus. It grows well and fast, has only simple leaves and is significantly hardier than the citranges 'Rusk' and 'Morton'. Its flowers are small, comparable to those of tangerines. B. Voss says about 15 clones labeled HRS and a capital letter, of which the clone 'HRS-899 J' is supposedly hardy to -15°C and the clone 'US 899 F' has much more vigorous growth. Its leaves mono-, di- and trifoliate and it’s a little bit hardier.

kumin

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Re: F2 citrange winter hardiness trial
« Reply #37 on: February 03, 2019, 03:30:55 PM »
Today's high temperature is 45deg. F. I've taken a few photos to see how the best plants have fared. Most look similar, but a little worse for wear and tear. The best ones look to be in similar condition to my Poncirus of similar size. These may have a chance at survival.

This is after almost a week of temperatures below freezing, the lows ranged from +3 deg. F. to -11.8 deg F., there were several days of high temperature +/-  +15 deg F. I am pleased with the results thus far, but percentages of plants looking this good are low.
Of special interest to me is plant # 3 having a mixture of unifoliate and trifoliate leaves.









« Last Edit: February 03, 2019, 03:42:57 PM by kumin »

SoCal2warm

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Re: F2 citrange winter hardiness trial
« Reply #38 on: February 03, 2019, 05:47:57 PM »
This is after almost a week of temperatures below freezing, the lows ranged from +3 deg. F. to -11.8 deg F.,
It's surprising that anything that's not pure poncirus could survive -10 F.
I'd view this as a success.

kumin

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Re: F2 citrange winter hardiness trial
« Reply #39 on: February 03, 2019, 05:58:59 PM »
At this point I'm debating protecting a few of the most promising specimens for the rest of the winter, in order to preserve their genetics. It would be a deviation from my original plan, but I already have $2,000.0 in this project and it might be prudent.

Although I can be certain that the seed parent is F1 C-35 citrange, there is no proof that the pollen parent is definitively the same. Depending on blooming time and seed grove layout, the pollen parent could be  potentially be a citrumelo, or different citrange.
« Last Edit: February 03, 2019, 06:21:08 PM by kumin »

Citradia

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Re: F2 citrange winter hardiness trial
« Reply #40 on: February 03, 2019, 07:11:51 PM »
The damage won’t show right away. The leaves and green in the branches will slowly turn brown starting at tips and the dead brown tissue works its way down to the trunk and then to the ground. I’ve had trees stay green until spring and then die. Look for cracks in trunks near the ground. If cracks form in trunks, probably gonna die. -15 degrees F and below freezing for a week, unprotected seedling poncirus hybrids, no. Miracle if some make it, and I would love to buy a specimen from you. I wish you the best in your endeavors.

Ilya11

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Re: F2 citrange winter hardiness trial
« Reply #41 on: February 04, 2019, 03:15:35 AM »
At least some of them will sprout from the roots. For me, the most promising is  the last plant, for the first three the stems are already damaged.
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                       Ilya

kumin

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Re: F2 citrange winter hardiness trial
« Reply #42 on: February 06, 2019, 08:04:37 AM »
Here are 2 photos showing responses of:

 # 1: F2  citrange seedlings and  the variability in cold resistance after a cold week with a low of -11.8 F. at the lowest.

 # 2: Poncirus  that hadn't dropped it's leaves.  Observed on a plant not fully hardened off.





mikkel

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Re: F2 citrange winter hardiness trial
« Reply #43 on: February 06, 2019, 08:33:31 AM »
wow, if it stays like that you found your hardy F2 hybrid.

kumin

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Re: F2 citrange winter hardiness trial
« Reply #44 on: February 06, 2019, 09:11:25 AM »
Thanks, I am hopeful. Both photos were taken today and both plants were exposed to the same temperatures. I realized that there are still many weeks until April 1. when I consider all danger to be past.

I have noticed that the slight red color where the leaflets join is not an indication of cold adaptation, but rather an indication of tissue damage.

Poncirus indication of cold damage closely parallels that of the citranges. A few of the citranges appear to have hardier leaves than the Poncirus progenitor, this may only be because Poncirus would have dropped it's leaves at that degree of maturity on that position of the stem.

kumin

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Re: F2 citrange winter hardiness trial
« Reply #45 on: February 08, 2019, 04:34:39 PM »
This continues to be an educational experience. The local cold weather has been followed up by warmer temperatures and rain.
 A few observations:
1. Poncirus leaves and twigs that appeared to be wilted and dying have re-hydrated remarkably quickly.
2. The combination of direct sunlight and frozen soil is very dehydrating.
3. Subzero temperatures with no wind on a clear night allows a super-chilled  layer of air to form directly on top of the snow, which is very harmful, this layer was about 6" deep. I don't have record of the actual temperature of this layer, as the reading of -11.8 F. was about 30" above the snow.
4. The section of the stems above the bottom 6 inches showed considerable less damage than the lower 6".
5. The rather quick warming trend allowed some damage to be visible within days.
6. Some bark splitting is becoming apparent.
7. There will likely be additional observations over the next 6-7 weeks, perhaps longer.
8. Photos of Poncirus before warm up and after warmup and rain. This should be the same twig.
9. This Poncirus tree was planted in the early 90's.




« Last Edit: February 08, 2019, 04:41:37 PM by kumin »

Millet

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Re: F2 citrange winter hardiness trial
« Reply #46 on: February 09, 2019, 11:34:17 AM »
Kumin, excellent post, very detailed.

kumin

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Re: F2 citrange winter hardiness trial
« Reply #47 on: February 15, 2019, 12:10:08 PM »
After a new survey of the F2 citranges, I remain cautiously optimistic. The best looking plants remain quite consistent, although a portion of previous candidates look less promising. The best contenders are likely well under 1 percent of total plants.

One factor in their favor is the fact that our area has had record high moisture levels since July of 2018. The plants should have been well hydrated at any time the soil hasn't been frozen. An other unanticipated factor may be the black plastic film used for weed control. I suspect this will lessen the freeze/thaw effects to some degree.

There's an attached photo of a Southern Magnolia cv. 24 Below. This is included to gauge the impact our cold event had on other plants with hardiness similar to Poncirus. All cold damaged leaves will be shed during the May flush of new growth.



 

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