Subject: seed vitality after storage

From: [email-masked] (Mary Anne Lynch)
Date: Wed, 1 Nov 1995 03:35:46 GMT

Hello,

I have some questions about seed vitality and I am hoping this newsgroup
is the proper place to post them.

Since seeds continue the respiration process before they are planted,
they continuously lose their 'nutrient store' (albeit slowly) until
one day they just will not have any more energy to germinate.  I'm
just stating this as a fact; please correct if anything is amiss.

Now, say you plant two seeds of idential varieties - one is fresh, and
the other has been in storage for a long time, but has just enough
energy to germinate.  Both seeds are treated identically.

My question is:  Will the seed that was stored
produce a plant that is as healthy as, *or* not quite as healthy as,
the plant produced by the fresh seed?  If both are quite healthy,
is this because once they emerge from the ground, photosynthesis
takes over, and it doesn't matter how much 'energy' was left in the
seed, just as long as it had enough to germinate?  Or, will this
stored seed produce a plant that will forever be inferior to the fresh
seed?

If you plant a bean seed, for instance, you can watch the cotyledons
slowly shrivel as the seedling matures, so I assume that any nutrients
are being extracted.  But is this process not inferior to the energy
that the green parts of the plant are producing through photosynthesis?

Thanks for any opinions you can offer.

Mary Anne Lynch
[email-masked] -OR-
[email-masked]
*The road to enlightenment is long and difficult...so bring snacks
and a magazine.*

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From: [email-masked] (Thomas Bjorkman)
Date: 1 Nov 1995 20:17:27 GMT

In article <[email-masked]>, [email-masked] (Mary

> stored seed produce a plant that will forever be inferior to the fresh

As seeds age, their ability to germinate does indeed drop.  Before they
lose their ability to germinate, their vigor declines.  Their ability to
germinate can be measured accurately and repeatably.  In fact, the
Association of Official Seed Analysts publish the specific riteria that
are to be used to measure particular seed lots, and it is the results of
these tests that are printed on seed packets.  

Higher germination numbers mean that more seeds will germinate, but it
often also means that they will have higher vigor.   It would be nice to
have some vigor number printed on the packet, but that has been very
difficult to meaure accurately--it depends on too many other things also.

Aging happens at different rates depending on storage conditions, hot and
wet being harder on the seeds.  The rates of decline have been determined
for many species and can be calculated for a given set of conditions from
what are known as the "Roberts equations", from a series of papers and
monographs published by Roberts and Ellis. These are useful, but there's
more to it.  Some of that is in a really interesting book by David
Priestley (Seed aging : implications for seed storage and persistence in
the soil, 1986, Comstock Associates: Ithaca, NY).

Does the vigor decline so fast that it is a problem?  One example is in
tropical Mexico where corn is an important crop.  With the heat and
humidity, some of corn varieties will lose as much as 20% germination and
a substantial amount of vigor in the 5 months between harvest and next
season's planting.  That is big trouble.  

Seedlings need to get off to a good start to make a strong plant.  Low
vigor seeds (with less energy and more internal damage) don't make
seedlings that get off to as good a start as fresh high-vigor seeds.

-- 
Thomas Bjorkman    Dept. of Horticultural Sciences   Cornell University

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From: [email-masked] (marc meyer)
Date: 1 Nov 1995 23:17:13 GMT

> stored seed produce a plant that will forever be inferior to the fresh

I think the answer to this question can be explained by the multitude of
seed size experiments which have examined the relationship between seed
size, which correlates with the amount of stored energy in a seed, and
adult plant characteristics.  In these experiments it was shown that small
seeds produced smaller seedlings and larger seeds (within the same
species) produced larger seedlings, but that this correlation dimished
rather quickly with time.  Thus, by the first or second week of growth,
the seedlings and subsequent adult plants produced from small and large
seeds were indistiguishable from one another with respect to all
externally measureable characters (i.e. plant height, plant dry weigth,
reproductive output, etc.).  Nevertheless, in some follow-up experiments
that examined this relationship in a more competitive environment (=higher
density of plants), it was found that seedlings from larger seeds did
significantly better than seedlings from smaller seeds (within the same
population).  More specifically, large seeded species produced adult
plants with higher survivorship, greater height, more leaves and more 
flowers than their small-seeded counterparts. 

So how does this relate to stored vs. fresh seeds?  Well, *assuming* the
relationship between stored vs. fresh seeds to be equivalent to that of
small vs. large seeds (in terms of stored energy reserves within the
seed), we could conclude that stored seeds, like small seeds, are just as
"healthy" as their fresh (or large) seed counterparts.  This is likely
because, as you stated, photosynthesis takes over and the amount of
initial stored energy in the seed becomes unimportant after the first week
or two of growth.  However, if this newly-germinated seedling finds itself
in a high-density, highly competitive environment, then the amount of
stored energy in the seed is going to be of crucial importance to the
growth and survival of that seedling.  Thus, a stored seed may be at a
competitive disadvantage to a fresh seed and may remain competitively
inferior (i.e. fewer roots to take up water and nutrients or a shorter
stature that allows it to be shaded out by taller intraspecific
competitors) throughout it's life.  So, in answer to your last question as
to whether a stored seed (with fewer energy reserves) will produce a plant
that is forever inferior to the fresh seed plant (with greater energy
reserves), I would probably say yes, but only if there is relatively
intense intraspecific competition going on between these two seed types. 

Cheers,
Marc Meyer
[email-masked]

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From: J Dudley Leaphart <[email-masked]>
Date: 1 Nov 1995 18:37:30 GMT

Mary,

This is a very good question, maybe I can talk my cohorts into doing a 
side by side study on some wheat seeds. It would be interesting to see if 
there are true differences. I do see emergence differences on old stored 
seed compared to say the current year's crop. The seeds germinate but are 
sometimes slower and without the vigor to emerge as fast as new seed.

I'm sure that some poor grad student has done his masters on this.

-- 

   Dudley Leaphart          Billings, MT          [email-masked]

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From: [email-masked] (JWGruber)
Date: 2 Nov 1995 09:48:56 -0500

I have recently been germinating some 33 year old seeds of morning glories
(Ipomoea violacea = I. tricolor) that had been stored in an ordinary box
in a closet for all those years. I found that while viability was very low
(< 1%), the odd seed or two that does germinate appears to do so quite
quickly (24 - 48 hours) and emergent hypocotyl looks strong and healthy.
The problem I encountered several times, however, was an inability of the
new seedling to shed its seed coat, with the resultant failure of any
epicotyl / embryonic shoot emergence and consequent death of the seedling.

John W. Gruber
Philadlephia College of Pharmacy & Science
[email-masked]

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From: [email-masked] (Jonathan B. Marder)
Date: Thu, 02 Nov 95 06:29:28 GMT

In article <[email-masked]>,
   [email-masked] (Mary Anne Lynch) wrote:
>one day they just will not have any more energy to germinate....

You may be interested to read up on "reconditioning" treatments. Seeds 
are partially rehydrated (using a strong osmoticum, usually polyethylene 
glycol), incubated for some days and then redried. When allowed to fully 
rehydrate, the treated seeds germinate faster and more uniformly. I 
believe that this is used as a commercial treatment.

I used this technique for my undergraduate project a 
loooooooonnnnnnggggg time ago. In my case, I looked at rRNA fragmention 
in "aged" tomato seeds and showed its repair during the reconditioning 
treatment. I haven't followed the literature about seed treatment, but 
here are some old references:-

Heydecker, W., Higgins, J. and Gulliver, R.L. (1973) Accelerated 
germination by osmotic seed treatment. Nature 246, 42-44

Heydecker, W., Higgins, J. and Turner, Y.J. (1975) Invigorastion of 
seeds? Seed Science and Technology, 3, 881-888.

Jonathan B. Marder                 '
Department of Agricultural Botany  |     Internet: [email-masked]
The Hebrew University of Jerusalem | /\/
Faculty of Agriculture             |/  \ Phone:    (08 or +9728) 481918
P.O.Box 12, Rehovot 76100, ISRAEL  /     Fax:      (08 or +9728) 467763

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From: [email-masked] (Thomas Bjorkman)
Date: 1 Nov 1995 20:17:27 GMT

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From: [email-masked] (marc meyer)
Date: 1 Nov 1995 23:17:13 GMT

Cheers,
Marc Meyer
[email-masked]

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From: J Dudley Leaphart <[email-masked]>
Date: 1 Nov 1995 18:37:30 GMT

Mary,

--

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From: [email-masked] (JWGruber)
Date: 2 Nov 1995 09:48:56 -0500

John W. Gruber

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From: [email-masked] (Jonathan B. Marder)
Date: Thu, 02 Nov 95 06:29:28 GMT

Jonathan B. Marder                 '