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Re: HYB: germination - "no" chill

  • Subject: Re: HYB: germination - "no" chill
  • From: irischapman@aim.com
  • Date: Fri, 26 Jun 2009 22:42:26 -0400

Stratification of seeds (chill period while damp) is like vernalization of plants. Same biological activity to achieve an end. Plant accumulate chilling hours until it reaches point it needs for activity. No hours accumulate when plant/seeds frozen. Hours accumulated between 0C -15C (32F-60F). Some plants /seeds can even use higher temperatures. Ideal is around 3-10C (40-50F). These hours of accumulated chill can be reset to "0" accumulated hours by seeds drying out or by a number of days with temperature above a certain criteria. Varies from species to species, but usually around 20C or about 72F max temperature for three days in a row. You also have to remember that there are two types of dormancy, photoperiod and daylight triggered ( actually a third governed by plant activity, but not relevant here.) How this translates to seeds is a bit of speculation, but I suspect the temperature dormancy seeds would start to grow whenever temperature warms up, after necessary stratification chill time, and be subject to drops in temperature, where as photoperiod ones wold wait for a more delayed and specific accumulation of chill hours.

Add to this another factor. That is with vernalization, and stratification, there is facilitative and obligatory. With obligatory, there is no plant bloom (vernalization) and with seeds no germination until the full number of chilling hours are accumulated. With facilitative, the chilling helps bloom (vernalization) or with seeds it helps seed germinate. If hours of chilling not reached, there will still be seed germination , but it will take longer before seeds germinate.

This brings up an additional factor. The method of seed storage before planting can with some species, reduce need for chilling hours. An example of this, is with daylily seeds. Some seeds need chilling before germination, yet some of these same seeds when held at room temperature for a couple of months, will germinate without chilling hours.(Study published in Daylily Journal) This is probably an example of facilitative stratification. the room temperature gradually reduces need for chilling hours.

One more, of a number of factors to consider, is our human effect on evolution of chill factor needs. A number of hybridizers only use first year germination seeds, so the ones requiring a second winter are being bred out of our current stock. Also, the more hybridizers there are from California, the more plants are selected that have lower needs for chilling hours. the less chilling hours are needed. And frankly, these plants from warmer climates are used extensively in current breeding.

For you John, there could be a strong selection factor for low chill hours and/or reduction of needed chill hours by room temperature storage. That is, you use seeds that germinate rapidly, so seeds from your own breeding are increasingly better germinators for your conditions. So I would speculate that seeds from cultivars that have heavy California blood, that the chilling requirements would be less then ones with more northern blood.

A further speculation, is the John and Mike store their seeds at room temperature all winter, before planting in March. Thus reducing need for chilling hours. In order to put germinating seeds into their own individual pots and grow and take care until August can only be done if you have a limited number of seed pods to take care of. I counted tonight, I have 300 pods planted from 2008. Germination ranges from 0, for about 30 pods, which went into barn fridge for summer. Of the others I have between 5- 50 plants germinated , or about 4-8,000 plants. They just can get this amount of individual attention.

Linda, I suspect your procedure has some elements that make germination slower. ie: occasional drying out which resets chilling hour clock. Or perhaps too early a harvest coupled with putting unshelled pods into burritos. I can't see any benefit of not shelling pod before placing in cold environment. Ripe seed pods should be starting to turn brown, or be starting to open before harvesting. To check on ripeness of seed pod, I squeeze lightly. If it squeezes easily (is starting to go soft) it is ready to be harvested. A little bit of practice will make this method work well for you. Seeds will be brown when pod is opened.

Food for thought, and probably more then you wanted to know.

Chuck Chapman

Date: Thu, 25 Jun 2009 14:55:56 -0400
From: "John Bruce" <jbruce1@cinci.rr.com>
Subject: Re: [iris] Re: HYB:  germination - "no" chill

Looking back over the archived climate data for the period between planting
and getting
green shoots, there were a total of 14 nights with temps between 33 and 40
degrees. Most of
those were in the first two weeks of the 6 week period. 4 were in the second
two weeks and 3
in the final two weeks. The total rainfall for the period was 5 inches, with
the bulk of the days
being measured less than .05", and 14 days with .20" to .66". We dipped
from above 40 to below 31
degrees 8 times during those six weeks. The interesting change was the week
before sprouts started appearing.
In those 7 days there was no rain, and nighttime temps were steady in the
range of 59-64 degrees. The
2 weeks prior to that had temps hovering at 43 +/- 2 degrees with two nights
at 54, and two at 38.
Note that the temps represent lows, not averages for the nights...that is to
say on a 40 degree night it may have
only reached 40 for an hour or so. And while moisture was constant, I would
not call it copious. I had always
heard you needed vast quantities of water to leach out inhibitors. I believe
that may be why I had such poor
germination back in the mid 90s...I watered daily only to have few sprouts
and many empty seed husks.

John, from what was posted here previously (assuming I remember
the temperature required for removing germination inhibitors is below
40oF. Once temperatures drop (much?) below freezing, the process
So seeds could stay frozen for a long time and still need the

Do you know how many days with at least night temperatures below 40oF
spring planted seeds experienced before germinating?


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