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Re: weeds


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Does anyone have any literature references on the local genotype issue?
I am putting together a reference list on this subject.  Any information
would be much appreciated.


E) IMPACT OF CROSSING 'NATIVE' SPECIES COLLECTED FROM AFAR ON LOCAL
POPULATION GENETICS
Keller, M., J. Kollmann and P.J. Edwards. 2000. Genetic introgression
from distant provenance reduces fitness in local weed populations.
Journal of Applied Ecology 37(4): 647-659.
The authors studied the performance of the offspring of three ruderal
species native to Switzerland that were intentionally crossed with pollen
from populations native to distant parts of Europe. Most of the first
generation crosses exhibited improved performance in terms of biomass
and/or seed size relative to to that of both parents when grown in common
plots (heterosis, aka hybrid vigor). However, the second generation
backcrosses (native Swiss plants crossed with pollen from the F1s) almost
all showed reduced performance in terms of biomass and survival relative
to both parents. Analysis of the data indicated the reduction in
performance was due to the breakdown of adaptive gene complexes which
were apparently present in individuals from the native population and
which wree disrupted by outbreeding with individuals from other
populations. The authors point out where reduced performance is the
result of certain poorly adpated genes from the ditant populations these
genes will be selected against and so the damage seen will decrease with
each backcross. On the contrary, where the reduction in performance is
due to the breakup of co-adapted gene complexes from the native
population the damage is likely to increase with each backcross for at
least several generations. The authors discuss the implications of these
findings and other studies for the use of plants, seed and pollen
collected from distant sites for restoration projects, noting that small
native populations are especially vulnerable to 'genetic assimilation'.
However, they are unable to come up with general guidelines regarding
what is an acceptable distance from which native plants can be introduced
since population genetics vary so widely between the few species and
populations that have been carefully studied so far.

Check The 17th North American Prairie Conference Proceedings where a Seed
Source Issues Symposium Occurred.

Search for Elymus glaucus,there is a good article for which I do not
currently have a reference.

Michael Engel
US Fish and Wildlife Service
Private Lands Office
4511 Helgesen Dr.
Madison, WI  53718

608-221-1206 ext. 21




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