Tropical Fruit Forum - International Tropical Fruit Growers



Author Topic: Accuracy of cold hardiness temperatures?  (Read 1719 times)

Isaac-1

  • Member
  • ***
  • Posts: 68
    • western Louisiana zone 8b/9a line
    • View Profile
Accuracy of cold hardiness temperatures?
« on: January 09, 2018, 06:13:02 PM »
Over the last few weeks thanks to google  I have been reading scans of a variety of older 20th century scholarly works regarding growing citrus, and one of the things I noticed was a significant difference in reports of cold hardiness for various common citrus cultivars.  Not so much the absolute temperature values, but instead their relatively sequence  from most to least cold hardy.    One in particular that I noted, several of these mid 20th century works list Meyer's lemon as being almost as cold hardy as Owari Satsuma, which matches my observation of many people near where I live on the 8b/9a line having mature inground Meyers lemons growing in their yards that get no formal freeze protection yet continue to survive.

All of which leads me to ask, does anyone know of any modern detailed studies on cold hardiness of common citrus cultivars, I know there are many guides published by universities that list the often repeated numbers, but I have to wonder if that is all they really are, since based on comments on this and other web forums there seems to be a dependency in real world observations on cold tolerance of certain types of citrus, particularly Meyers lemons, and certain types of Grapefruit.

Millet

  • Moderator
  • Hero Member
  • *****
  • Posts: 2765
    • Colorado
    • View Profile
Re: Accuracy of cold hardiness temperatures?
« Reply #1 on: January 10, 2018, 12:33:33 PM »
At best the information on temperatures that a citrus cultivar can survive are general estimations.  Many, many variables contribute to the survive-ability during a cold spell.  Such as----the temperature just before the cold spell, the water content in the root zone, the age of the tree, the thickness of the trunk and branches, the wind, the length of the freeze, the health of the tree, the root stock, and the particular location the tree is growing in.    Grapefruit is generally listed as one of the more tender varieties, but one hears stories of the Dunstan grapefruit, which in reality is not an actual grapefruit, but rather a Citrumelo.

Walt

  • Member
  • ***
  • Posts: 57
    • USA, Kansas, Kanopolis, zone 6
    • View Profile
Re: Accuracy of cold hardiness temperatures?
« Reply #2 on: January 12, 2018, 03:11:21 PM »
Ilya11 had a related post on another thread a week or two ago.  It got me to thinking, and I've spent hours studying research papers on cold hardiness of apples and plums.  Similar papers came up on pears, peaches, and apricots when I searched on google.
So there is an amazing amount of information that  might matter.  Much of it rather discouraging to me, as in breeding hardier citrus, I need to be able to sort out those in each generation that are a degree or two more hardy.
First the good news.  My idea of testing cold hardiness of scion wood works with apples.  Good.
Now the bad news.  For such a test to work, the trees the cuttings are taken from must be from the same location.  And we all know that microclimates can vary even in small areas.  Fertility must be good in the ground where every tree was grown.  Rootstocks need to be the same.  If the cuttings were taken from own-root plants, then root differences may effect twig cuttings.
One study treated freeze damage and cold damage seperately.  Freeze damage is damage from sap freezing in the xylem.  Cold damage is damage done though the sap in the xylem hasn't frozen.  Spring and fall damage is often cold damage, not freeze damage.
I would like studies to be made of cuttings, scionwood-like cuttings, of different varieties and different species of citrus from different locations, tested different times during spring, winter, and fall.  I think the resulting data would be quite useful.  A little dorm-type refridgerater would be enough to test twigs of several trees at once.  I think a couple of days might be enough to test freeze damage at a given time and place.
Testing for tolerance to quick drops in temperature, then the temperature going right back up, like single overnight freezes, will be harder to sort out.

Walt

  • Member
  • ***
  • Posts: 57
    • USA, Kansas, Kanopolis, zone 6
    • View Profile
Re: Accuracy of cold hardiness temperatures?
« Reply #3 on: January 21, 2018, 03:12:55 PM »
Last winter many of pure P. trifolata seedlings died to the ground over the winter.  These seedlings had been planted in pots as seeds as soon as the fruit were ripe.  They were grown in a greenhouse over the first winter, then planted in the ground as soon as last frost date.
I had treated seedlings the same every year for 4 years, building up a supply of rootstocks, for 4 years with no problems so I blamed drought stress, not cold.  But since they had survived underground and came back up, I decided it was cold and drought stress combined, not one or the other.  Such little things can affect winter hardiness I think.
All seeds were from the tree and I think they are all geneticly identical.

So this year I am irrigating over the winter.  And yesterday I was out carrying water to the seedlings, since the summer automatic irrigation is shut off for the winter.  I noticed 3 out of 94 seedlings still had green, healthy leaves.  I have had over a week below freezing, dropping to -15C during 2 nights.  And green leaves still on my P.t?  The cold had broken and the last 5 days have been quite warm, dropping below freezing most nights but just barely freezing.  Freeze damage should have been seen by now if it had happened.
So I looked at my 3 and 4 years seedlings.  14 of 25 4 year old seedlings still have green healthy leaves.  Nothing I have been told or read prepared me for this.
I think that any report of trees living or dieing at a given temperature is of very limited value in another place,  I don't say it is of no value, because we often have no better information.  But there are many variables other than temperature and variety.

Ilya11

  • Sr. Member
  • ****
  • Posts: 267
    • France, Paris region, Vaux le Penil, middle of Northern z8
    • View Profile
Re: Accuracy of cold hardiness temperatures?
« Reply #4 on: January 22, 2018, 04:11:15 AM »
It is very common for the young seedlings of PT to keep green  leaves over the winter.
Moreover, in poncirus  nucellar seed formation  is not obligate. It depends on the season and variety, many of  seedlings are zygotic, giving plants different from the mother.
Best regards,
                       Ilya

Citradia

  • Sr. Member
  • ****
  • Posts: 489
    • USA/NC/Old Fort/6B
    • View Profile
Re: Accuracy of cold hardiness temperatures?
« Reply #5 on: January 22, 2018, 08:56:47 AM »
Walt, different individuals of a variety will perform differently over winter. Microclimate can be a factor, but I think different individuals from the same fruit grown from seed have varied cold hardiness in their genetics. I have dunstans citrumelos that all came from one fruit and out of 20 trees, some have frozen to death, some are currently 5 ft tall with green leaves planted on mountainside, and some are defoliated but still alive after the past three weeks of subfreezing temps here. My poncyrus flying dragon and regular PT almost always defoliate leaving a few leaves at top of trees even when we see zero degrees F. Remember that the poncyrus is dormant now and won't need as much water in winter, so don't over water. I leave my PT's alone outside in nature over winter just like any native deciduous tree and they don't get "cold damage."

Walt

  • Member
  • ***
  • Posts: 57
    • USA, Kansas, Kanopolis, zone 6
    • View Profile
Re: Accuracy of cold hardiness temperatures?
« Reply #6 on: January 23, 2018, 01:49:48 PM »
Thanks for the comments.
I live in winter wheat country.  Winter wheat that grows here is known for its drought tolerence.  Yet last year the wheat was damaged by drought over the winter.  So I think the combination of drought stress and cold was right.  Also the fact that I'd never had much winter die-back before.
As for microclimate, when I was hoeing up dikes around each plant to hold the water, some areas were moist and some were completely dry.  This within 2 m of each other. 
One winter old seedlings were more than 100 m from the 4 winter old seedlings.  Differences between locations include tree root competition, wind breaks, amount of sun, soil type, mulch vs. no mulch.  So it isn't fair to compare them at all. 
I had never seen leaves on P,t during the winter before, except in the greenhouse of course.  But I haven't really checked them before.  But last year was the first time I have seen winter damage.  From now on I'll be checking them all winter.

Zitrusgaertner

  • Member
  • ***
  • Posts: 59
    • Vienna, Austria, European Union 7b
    • View Profile
    • www.agrumi.at
Re: Accuracy of cold hardiness temperatures?
« Reply #7 on: February 23, 2018, 07:05:27 AM »
Ilya wrote,
"It is very common for the young seedlings of PT to keep green  leaves over the winter.
Moreover, in poncirus  nucellar seed formation  is not obligate. It depends on the season and variety, many of  seedlings are zygotic, giving plants different from the mother."

I am bewildered about this statement. How could PT build up a stable and quite homogenous population if there were a lot of zygotic upcome? I recently read in a scientific report that PT is likely to be an intergeneric hybrid not a genus of its own. That is why I assumed apomixis was the reason of its stability. Maybe I am totally wrong.

Regards Robert

Ilya11

  • Sr. Member
  • ****
  • Posts: 267
    • France, Paris region, Vaux le Penil, middle of Northern z8
    • View Profile
Re: Accuracy of cold hardiness temperatures?
« Reply #8 on: February 23, 2018, 10:24:54 AM »
Robert,
It really depends on the variety, some years ago I tried to evaluate the number of monoemryonic germinations in fruits of two ponciruses
Old plant from Jardin des Plantes de Paris



My poncirus (from B.Voss)
You

Some more reading on zygotic seedlings in poncirus
https://www.jstage.jst.go.jp/article/jsbbs1951/36/2/36_2_138/_pdf
https://www.jstage.jst.go.jp/article/jjshs/74/3/74_3_189/_pdf
https://www.jstage.jst.go.jp/article/jjshs1925/63/1/63_1_23/_pdf/-char/en
Best regards,
                       Ilya

Millet

  • Moderator
  • Hero Member
  • *****
  • Posts: 2765
    • Colorado
    • View Profile
Re: Accuracy of cold hardiness temperatures?
« Reply #9 on: February 23, 2018, 10:43:08 AM »
Flying Dragon is 50 - 60% true from seed.  True varieties have curled thorns, twisted stems and smaller leaves than non-nucellar seedlings. Further Flying Dragon produces higher quality fruit because slower growing rootstock.

Zitrusgaertner

  • Member
  • ***
  • Posts: 59
    • Vienna, Austria, European Union 7b
    • View Profile
    • www.agrumi.at
Re: Accuracy of cold hardiness temperatures?
« Reply #10 on: February 23, 2018, 03:14:10 PM »
Thank you, Ilya. But monoembryonic seedlings does not necessarily mean aswell zygotic. Monoembryonic seed might aswell be nucellar too. As far as I know.

RR

Ilya11

  • Sr. Member
  • ****
  • Posts: 267
    • France, Paris region, Vaux le Penil, middle of Northern z8
    • View Profile
Re: Accuracy of cold hardiness temperatures?
« Reply #11 on: February 23, 2018, 04:00:46 PM »
Sure, but please read the attached articles.
Best regards,
                       Ilya

Walt

  • Member
  • ***
  • Posts: 57
    • USA, Kansas, Kanopolis, zone 6
    • View Profile
Re: Accuracy of cold hardiness temperatures?
« Reply #12 on: February 23, 2018, 05:30:06 PM »
Useful information.  Thanks for posting the links.

Zitrusgaertner

  • Member
  • ***
  • Posts: 59
    • Vienna, Austria, European Union 7b
    • View Profile
    • www.agrumi.at
Re: Accuracy of cold hardiness temperatures?
« Reply #13 on: February 24, 2018, 04:18:04 PM »
Great informations, thank you Ilya. Very interesting. What do you know about origin (parentage) of PT? I found a remark that it may be a intergeneric hybrid between some Citrus and something else -but what would be likely? Another statement says it is within Citrus closest to C. reticulata and Fortunella. I collect information for a presentation about cold hardy citrus and citrus origin.

Regards Robert

Ilya11

  • Sr. Member
  • ****
  • Posts: 267
    • France, Paris region, Vaux le Penil, middle of Northern z8
    • View Profile
Re: Accuracy of cold hardiness temperatures?
« Reply #14 on: February 24, 2018, 06:20:19 PM »
For the moment nobody knows precisely the origin of poncirus.
 In the recent article you mentioned they used statistical methods to infer the relations between genomes. They made it both for the main part  of genome residing in cell nucleus and coming from both parents as well as cytoplasmic organelles like mitochondria and chloroplasts that mostly are inherited from the seed parent.
Statistics found some discrepancy between these two analysis  in the position of poncirus relative to other citruses.That is why they made a hypothesis that poncirus comes from the very old hybridization between two only distantly related plants. That happened long time ago and in the nuclear part of the genome the parts coming from these ancient parents were scrambled in such a way that you can not distinguish their precise origin. The situation is different for cytoplasmic part that is inherited only from one parent.
Best regards,
                       Ilya

Zitrusgaertner

  • Member
  • ***
  • Posts: 59
    • Vienna, Austria, European Union 7b
    • View Profile
    • www.agrumi.at
Re: Accuracy of cold hardiness temperatures?
« Reply #15 on: February 25, 2018, 09:45:03 AM »
Thank you, Ilya, you are a great source of knowledge   ;)

Best Regars
Robert

PS: my outdoor citri are gouin to be frost-tested these days  :-[

 

Copyright © Tropical Fruit Forum - International Tropical Fruit Growers