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4. GENETIC DIVERSITY...
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4.4. DISCUSSION
4.4.1. Genetic variation in L. multiflorum and L. perenne
The genetic polymorphisms observed in populations are the products of various evolutionary
forces in their long history. Thus, the extent of genetic variability is characteristic for
each species but ecological and life history factors have an effect on plant population genetic
structure. The average proportion of polymorphic enzymatic loci (P) in plants is about 46%
(Futuyma 1986), the mean number of alleles per locus (A) is 1.53 and the mean gene diversity
(H) - 0.113 (Hamrick and Godt 1989). However, it has been well documented that much
higher genetic diversity exists in out-crossing species. In Trifolium for instance, allogamous
species have three times more polymorphic loci in comparison with autogamous ones (73%
and 27%, respectively) and the number of enzymatic alleles is almost doubled (2.1 and
1.2). Likewise, the total (H T
=0.343) and within-population gene diversities (H S
=0.249) are
significantly higher in the former (Bulinska-Radomska 2005). By contrast, the proportion of
polymorphic loci in self-pollinated species tends to be very low even thought high-throughout
technologies have been applied. Only 2.3% of polymorphic AFLP bands have been found
in annual, inbreeding grass Bromus tectorum (Ramakrishnan et al. 2004) but no monomorphic
AFLP band has been observed in out-breeding Pseudoroegneria spicata (Larson et al.
2004). Similar results have been obtained with RAPD or ISJs markers. As many as 83% of
polymorphic loci have been detected in Pinus cembra from the restricted area of the Tatras,
despite the fact that this population is very small (Chmiel and Polok 2005). The genus Lolium
grouping both autogamous and allogamous species is not an exception. As it can be concluded
from mainly enzymatic studies the genetic structure of inbreeding and cross-breeding
species is completely different (Table 4.8). Very low electrophoretic variation has been found
in self-pollinating species concluding from the average 6% of polymorphic loci, 1.08 alleles
per a locus and gene diversity equal 0.029. Accordingly, the majority of populations are completely
fixed for a single allelic variant (Loos 1993b). However, none of enzymatic variants
present in inbreeding species is unique, all have been also found in cross-breeders (Polok
2005). By contrary, allogamous species are highly variable with 76% to 91% of polymorphic
loci, 2.13-3.25 alleles per a locus and the average gene diversity 0.277-0.405 (Table 4.8).
L. rigidum has proved to be the most variable species. Therefore, a high degree of enzymatic
variation recorded in L. multiflorum and L. perenne in the present study and reflected by 80%
of polymorphic loci, 1.81-1.96 alleles per a locus and the total gene diversity about 0.340 falls
well within the range typical of allogamous, wind-pollinated Lolium species.
Analyses of extensive data compilations have demonstrated that allozyme-derived population
genetic parameters are comparable across studies. But they have suffered from a relatively
low number of loci and might provide misrepresentative estimates of genetic variation
because the availability of histochemical stains has been a deciding criterion for the inclusion
in electrophoretic surveys. In the present research 15 enzymatic loci were identified of which
12 were polymorphic (80%) in L. multiflorum and L. perenne. With virtually unlimited amount
of potential markers, DNA based methods provide much more efficient tool to disclose genetic
diversity in any population and species. The present results have shown that genomes
of L. multiflorum and L. perenne harbour a wealth of variation on DNA level. The resolution