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RE: seed genetics (a hopefully not to boring response)


Plant populations while still the same spp. can have vastly different
genomes between populations and within as well.  
It works both ways.  I have been involved in genetic studies of
populations of Emex australis  (doublegee and numerous other common
names) over a six year period.
We looked at populations from all over its native South Africa and
populations from all over Australia probably in excess of 60 seperate
populations.  The pupose was to see it we could identify the particular
region of South Africa the Australian populations had originated from
and then search those regions for biological control agents.  The
genetics of a plant can be so specific at times that diseases, insects
etc can vary from region to region.  Interestingly this spp. shows very
little genetic diversity.  There was only one population in Australia
that showed a slight single gene expression in difference and the South
African populations showed three types but the most common and
widespread there was the common one in Australia as well, no suprises!
We were conducting isozyme assays in starch gel electrophoresis (for
those interested in the method)
This technique is very cheap and easy to do but a devil to get
consistent results so we repeated and repeated untill we had results we
could rely on (about 2 and a half years work and we could only afford to
look at about 15 enzymes, which would represent only a fraction of the
total genetic code of any spp.)
During this time we also looked at several regional populations within
Western Australian in some detail.
One from the north, one from the south and one from a central area, this
seed was all stored in the same place and tested for germinability each
month for several years.
After establishing that the WA populations were more or less genetically
similiar we were rather suprised to find differing responses in seed
dormancy between these three populations.  The seed collected from each
region went through cycles over a four year period, there were periods
of high germinability followed by a drop in germinability.  The cycle
duration and frequency varied greatly between populations and we could
only put these differences down to an environmental effect at the time
of seed maturation.  To further test this we collected seed grown from
each of these populations under indentical conditions and tested their
dormancy cycles again, they were the same!

This raises many issues relating to province variation/ population
genetics, are they genetic or environmental differences we see
expressed?
Think about the variation that we have been able to achieve with plants
just from the same spp.
Cabbage, brussel sprouts, cauliflower, Kale, Kohlrabi, Broccoli all the
same spp.  Bassica oleracea!
and the wild form is just a weed!  

Many of the natives in Western Australia show similiar regional
variations for the same spp. 
A classic is Eucalyptus todtiana,  a lovely tree up to 10 meters around
Perth and further south, yet north of Perth in the heathlands around
Eneabba it never gets higher than 2 meters, and its not just
environmental effects at work here.  

Population genetics is a huge field and in the case of most plants only
the surface has been scratched.
Most of the horticultural and agricultural spp. today have been bred
using the same basic principles that  animal breeders have used over the
centuries, selecting parents and crossing  to enhance traits. It isn't
nessercary to know much about genetics just how to recognise the traits
you wish to breed for and the mechanics of the breeding systems.

I guess I haven't answered many questions here but it is an interesting
area.
oh for those wondering Genotype refers to an individuals genetic pattern
or code
Phenotype is a common form or trait shared or expressed  by a
population.
So a population may share a Phenotype but each individual has their own
Genotype
Even in a crop as seemingly genetically identical as wheat there will be
some genome variation between individual plants.

Hope you haven't fallen asleep
Cheers, Rod

Rod Randall
Weed Risk Assessment
Weed Science Group, Agriculture Western Australia
Home Page  http://www.agric.wa.gov.au/progserv/plants/weeds/Weedsci.htm

             "I weed..."

> ----------
> From: 	Daniel Segal
> Reply To: 	Daniel Segal
> Sent: 	Friday, 6 March 1998 4:52 AM
> To: 	medit-plants@ucdavis.edu
> Subject: 	seed genetics
> 
> 
> 
> though i am no geneticist to say the least, it is obvious that by
> virtue
> of sexual reproduction each individual in a population is genetically
> unique.  The same is true of populations within a meta-population or
> region--each population is genetically distinct.  The question really
> is
> one of degree--how distinct are they from eachother?  Though it can
> never
> hurt to use site-specific seed and plant material, more often than not
> for
> any given species, the severity of this genetic differentiation is
> unknown.  For restoration I think the attitude has been "better safe
> than
> sorry", and this is good but clearly not scientific. 
> 
> Furthermore, regarding the northernmost Big Tree groves in Placer Big
> Trees, there are several young individuals which were planted by an
> ambitious and well-meaning group years ago, but the seed was from
> southern
> groves of Sequoiadendron.  Lately there has been a lot of noise about
> removing the imports, so that their pollen does not sire north-south
> Big
> Tree offspring.  Again, probably better safe than sorry, but does
> anyone
> know for sure that the infusion of some slightly different genome into
> this grove will be detrimental?  Is nature as simple as that?  The
> variables are so many, not just mean annual temp. or mean July temp.,
> that
> we can't possibly know until we try.  I don't advocate vigilanteism
> with
> regard to the genetics of California's populations of all species, but
> gene flow is natural, even if we sometimes drive it...
> 
> dan segal
>
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