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The aim of this study is to assess the impact of
different agricultural regimes on the genetic
diversity of plants, using the model plant
Arabidopsis thaliana (Fig. 1) as an indicator
species. Population samples of A. thaliana were
taken from a variety of locations in the
Lahn-Dill hill-country region in central Germany.
These sites vary in their agricultural histories
and can be categorised into four types intensive
agriculture (I), extensive agriculture (E),
meadow (M), and fallow land (F). Using AFLP
(amplified fragment length polymorphism Fig. 2)
and microsatellite markers (Fig. 4) for
population genetic analysis, the hypothesis is
being tested that intensive agriculture reduces
genetic diversity.
AFLP Results
Microsatellite Results
Fig. 4 Analysis of the microsatellite locus
nga128 in A. thaliana samples from extensive,
meadow and fallow populations. In this example
two heterozygotes are observed (arrows) along
with a number of different homozygous alleles. On
average, 13.2 alleles were observed per
microsatellite locus. This is noticeably higher
than results found previously in similar studies
(4.1a, 5.3b, and 10.6c). a Bell Ecker (1994)
Genomics 19 137-134 b Todokoro et al. (1995) Jpn
J Genet 70 543-554 c Innan et al. (1997)
Genetics 146 1441-1452
Fig. 5 Expected and observed heterozygosity
calculated from microsatellite data. Observed
heterozygosity was significantly (plt0.001) lower
than the expected values, showing that the
populations are not in Hardy-Weinberg equilibrium
probably due to the high self-fertilisation
rate of A. thaliana. However, the level of
heterozygosity in the intensive population was
significantly lower than the other three
populations (p0.03).
Fig. 2 AFLP amplification of pooled DNA samples
from the four populations I, E, M and F. The
pools were tested with 36 primer combinations (12
shown here). In total 209 polymorphic loci were
detected. Bands were scored as present (1) or
absent (0) and analysed with the programme NTSYS
to determine genetic similarity (Fig. 3).
Conclusion and Outlook It appears from the
preliminary results presented here that intensive
agricultural systems may reduce genetic diversity
in natural plant populations. Although allele
frequencies showed no significant differences
among the different agricultural regimes, a
reduction in heterozygosity was observed in the
intensive system, perhaps due to reduced
outcrossing. Further data is being collected in
another year of tests to corroborate these
findings. A similar study of Viola arvensis
populations from the same sites will be
undertaken to provide an across-taxa comparison.
The genetic results will ultimately be compared
to results from a simultaneous phenotypic study
of the respective populations. Based on the
findings, predictions will be made regarding
selection and speciation mechanisms in natural
plant populations in agricultural ecosystems.
Fig. 3 UPGMA dendrogram showing genetic
similarities between A. thaliana populations.