Date: Tue, 16 May 1995 09:59:00 -0700 (PDT)
Sender: "Pallais, Noel" (N.PALLAIS@CGNET.COM)
Subject: Dormancy: Comments by Ellis on dormancy and vigor
I am curious about studies where dormancy and longevity in air storage were negatively correlated. May I have the reference of Prof Roberts?
I understand the lack of casuality between dormancy and longevity. Some genotypes of potato have low seed dormancy and high seed longevity (e.g. hybrids of "Atlantic" x XXXX).
I also understand how dormant seeds could find many ways to die before losing dormancy (fire, flooding, fungus). We killed seeds at >50C with high mc before they completely lost dormancy.
I also understand how dormant seeds can germinate before losing dormancy. When potato seeds are hydrated for a sufficient period of time under a narrow temperature range (17C+-3C) they will eventually germinate and produce "dormant" seedlings (i.e. dwarfed and slow growth). Moreover, when dormant seeds are treated with GA the allowable temperature range for dormant seeds is slightly broadened, albeit, seedling development is still suboptimal.
Nonetheless, the evidence we have shows when dormant potato seeds are stored at 40C or below, they do not seem to age until dormancy has been lost. A pragmatic hypothesis which might be important to test at the International Potato Center could be; long-term storage of sexual potato seeds in the germplasm collection should attempt to preserve seed dormancy.
Noel Pallais
CIP, Peru
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Date: Wed, 17 May 1995 08:25:16
Sender: R.H.Ellis@reading.ac.uk (Dr. Richard Ellis Agric Reading)
Subject: Re: Re. Comments by Ellis on dormancy and vigor
his book in 1972 gives the references and there are several others since eg our paper in Ann BOt 1993 vol 72 pp 583-590.
Richard Ellis
University of Reading, UK
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Date: Wed, 17 May 1995 10:48:00 -0700 (PDT)
Sender: "Pallais, Noel" (N.PALLAIS@CGNET.COM)
Subject: Re. Dormancy (germplasm implications vs. survival in the wild)
Re. discussions on dormancy and vigor
Learning what the processes involved in dormancy are, is of key importance. Probably for all of you, basic research is your mandate. But my job working closely with potato seed physiology at the International Potato Center is just about 70% over now that we know that for using potato seeds to produce a crop of potatoes ASAP, dormant (freshly-harvested) seeds should be stored at 40C with 4% mc for at least 4 months or until >50% germination is obtained under 27C after 8 days (max). I write a simple pamphlet with only "40C-4%-4MO" and I need to move on. Thus, pardon my storming herein but I can not allow this opportunity to pass me by.
These comments were sparked by the statements made by Dr. Ellis "There is evidence in some species at least..." In some species it is clear while in others "the reverse can also be shown". We might be looking for one answer when perhaps there is more than one. Dormancy is only a concept. The causes could be physical, biochemical or both. Certainly the relationships, if any, between aging and dormancy would be affected by the causal factor. But it is possible to answer practical questions without formulating all encompassing conclusions. For example, we would like to tell our curator if what he has been doing, storing fresh potato seeds at 5C (preserving dormancy) is a good or bad idea for preserving the viability of his germplasm. I always felt it was a good idea, but after reading the comment made by Dr. Ellis I have my doubts; "especially those tree seeds which show considerable dormancy die under comparatively benign conditions but that non dormant seeds survive as seedlings".
Which brings me to a final point. I have had great difficulty in explaining to my peers that seed germination and seedling growth is not evidence of dormancy loss, in potato seeds "at least". Dormant potato seeds "behave" somewhat like Prunus sp do when improperly stratified seeds are forced to germinate. Our seeds also produce slow growing seedlings (root development is clearly suboptimal), except not "rossete" though stems have less hairs. Another typical characteristic is the progeny germinates and "grows" with a remarkable lack of uniformity. The same progeny with non dormant seeds, will attain >90% germination after only 4 days under 27/40C (21/3hr) and seedlings will grow to maturity just like potato plants grown from tuber sprouts do. These seeds obviously perceive a favorable environment for survival (first rains?). On the other hand, a dormant potato seed in the wild would be better off germinating erratically and producing slow growing seedlings to survive, rather than die under continuous hydrated cool conditions for a long amount of time.
Noel Pallais
CIP, Peru
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Date: Wed, 17 May 1995 15:57:12 -0400 (EDT)
Sender: "Dean Hively" (wdh3@cornell.edu)
Subject: RE: Dormancy (germplasm implications vs. survival in the wild)
In message Wed, 17 May 1995 16:19:57 -0400,
"Pallais, Noel" (N.PALLAIS@CGNET.COM) writes:
"Which brings me to a final point. I have had great difficulty in explaining to my peers that seed germination and seedling growth is not evidence of dormancy loss, in potato seeds "at least". Dormant potato seeds "behave" somewhat like Prunus sp do when improperly stratified seeds are forced to germinate. Our seeds also produce slow growing seedlings (root development is clearly suboptimal), except not "rossete" though stems have less hairs. Another typical characteristic is the progeny germinates and "grows" with a remarkable lack of uniformity."
Is there any data as to what controls the depth of this response? Do the seedlings eventually grow out of this dormancy, and resume a typical growth rate, or do they remain stunted throughout their growth and reproduction?
I am doing my masters research on inducing dormancy in clover and alfalfa seeds so that they can be sown into soy at the last cultivation (late June) and not exhibit significant establishment until at least Aug. 1st. Is it possible that there is a way of improperly inducing germination without breaking dormancy, and yet have the intercrop thrive after soy harvest on October? I would appreciate any suggestions for means of stimulating such a response. Uniformity is not necessary in a cover crop, but overall yield is important.
W. Dean Hively
wdh3@cornell.edu
331 Emerson Hall,
Cornell University
Ithaca, NY 14853 USA
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Date: 18 May 1995 14:29:55 -0500
Sender: "Mike Foley" (foley@btny.purdue.edu)
Subject: Re: Dormancy (germplasm imp
Reply to: RE>>Dormancy (germplasm implications vs. survival in the...
With reference to recent messages from Noel Pallais and Dean Hively -
Noel's observation that dormant potato seeds, which are induced (forced) to germinate, germinate "differently" than dormant potato seeds induced to germinate by afterripening (AR) is of interest to me (Mike Foley). I work with wild oat which also requires warm-dry afterripening to transform the seed (embryo) from a dormant to nondormant state. I have made the same observations on wild oat. If germination is induced with GA, wounding, fructose, etc. the physical aspects of germination and early development are "different". I contend that afterripening breaks dormancy while GA and the like induce germination of dormant caryopses. Basically AR removes the block to (normal) germination while GA action is to circumvent the block. I believe the block is some factor, which among other things, regulates carbohydrate metabolism. Germination can occur in the absence of "normal" carbohydrate metabolism but the result is physical, physiological and molecular differences in germination. Some of this will be published in the Proceedings of the 1994 Plant Dormancy workshop.
After a certain period of growth after germination of a wild oat seed growth (rate and appearance) appear to be similar to that of afterripened seeds. To maintain the long-term viability of our wild oat inbred line seed stocks we store them at -20 degrees with DryRite to maintain dormancy. I am of the opinion that maintenance of the dormant state and longevity are highly related (thru a block in carbohydrate metabolism, i.e. sugars, vitrification, phase transitions). When we need plants we germinated dormant seeds in GA until radicle protrusion and then transfer into soil. The plants develop normally in the soil.
As to the question "Is there any data as to what controls the depth of this response" the answer yes and no. No, because no one to my knowledge knows what afterripening does or what the block to germination actually is. Yes, in that cool-moist conditions or short photoperiod increase the depth of dormancy of many small grain seeds. Trewavas (1988 Bioessays 6:87) published a conceptual model on dormancy in wild oat which I personally find appealing in terms of explaining many facets of dormancy in wild oat. No one to my knowledge has attempted to test the model.
A scientist in Canada, Vern Burrows, tried to create a crop call dormoats (plant in the fall grow in the spring). To my knowledge the concept did not work to well because dormancy/afterripening were not well controlled. I think Vern is a plant geneticist/small grains breeder. Contact one of your colleagues at Cornell to get a number to contact him for "the rest of the story".
Dean - have you talked to Anwar Khan (at Geneva) about your project. He reported on a way to make nondormant seeds dormant at the 1994 Plant Dormancy workshop.
Here is a question from me related to Noels comments on stratification of Prunis. I have always been under the impression that seeds that required stratification AND showed atypical germination/growth when forced to germinate had immature embryos. Is this a misconception? I think I got this impression from reading the literature on apple and peach. Many of our weed seeds in the Midwestern part of the U.S. require stratification for germination. I wonder if their germination/growth would be atypical if forced to germinate by some means?
Mike Foley
foley@btny.purdue.edu
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Date: Fri, 19 May 1995 09:02:00 -0700 (PDT)
Sender: "Pallais, Noel" (N.PALLAIS@CGNET.COM)
Subject: Response to Dean Hively from Pallais (dormancy)
I know of no data "as to what controls the depth of this response". If I were working in a University I would convince a student to do this research. All I can tell you from 12 years of observations is it appears dormancy loss is a progressive process with respect to the "wild" characteristic of seedling emergence. When seeds are freshly harvested the emergence spread could be 147 days as reported by Stier in 1936. But when nondormant, seeds emerge and attain a full cover just like any crop would or even better; fast (4 days at >25C), uniform and vigorous. With the last rains of the wet season potato seeds were conditioned to be cautious, but with the first rains after the dry season they were apparently selected to be bold! Thus "taming" (circumventing its wildness, i.e. controlling its dormancy) sexual potato seeds is the key for re-domestication of the potato for sexual propagation. It was possible 10,000 years ago to tame maize and wheat. I think it is possible today with the potato. Right now we are doing it not very differently that our "UGA-MUGA" ancestors must have done it. That's why we need all of your help.
Yes, dormant seedlings eventually grow out of their dormant-like growth and resume "normal" growth. I feel this occurs after juvenility. The problem is that harvest maturity is delayed and not uniform. For a crop seed this aspect is crucial. You say it is not important for the alfalfa June crop to be uniform, but I bet it would help if it was.
It is very interesting to me that your objective is completely the converse of mine. You want to induce dormancy! The question you pose, however, is a bit confusing. "Is it possible that there is a way of improperly inducing germination without breaking dormancy, and yet have the intercrop thrive after soy harvest in October?" Do freshly harvested alfalfa seeds exhibit a lower propensity to germinate under a given set of conditions, in which non-dormant seeds would have no problem germinating under? If yes, the answer might be in looking for storage strategies to preserve dormancy (for potato seeds it works at low moist and low temp). Does alfalfa have any wild relatives who have dormancy and who might be able to "lend" alfalfa these genes? Do you see variability in your seeds for this characteristic which might allow you to select in October after sowing in late June?
Induction of secondary dormancy could another possibility; for potato seeds this might happen at high moist and high temp or at low moist and low temp. Though, I am not sure if seeds without primary dormancy can acquire secondary dormancy? You might try light; quality and daylength-- during seed production, seed drying, or subsequent seed soaking. Maybe GA inhibitors applied to fruits or seeds. You can test other hormones, CK? Stage of seed maturity at harvest might also have an effect. Fermentation of seeds with fruits mashed, anaerobic works with potato seeds sometimes, but aerobic fermentation might work for you. A simple solution could be found in physical coverings which prevent oxygen and/or water diffusion, such as pelleting with degradable materials. You might want to test osmotic priming at near lethal levels? Or play with other seed treatments that are known to work but only within discreet limits; and test those limits! You might just find some alfalfa seeds retain "remembrance" of the secondary dormancy strategy which allowed them to be one of the more than 200,000 species that survived, starting 30 million years ago. Another factor which might exert some influence is the location site of seed production. In general, longer daylength sites produce more dormant seeds, but I am sure the converse could also very well be true.
Good luck! Please keep me posted I am very interested in the progress you make. Maybe I will think of something I left out and will let you know.
Noel Pallais
CIP, Peru