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4. GENETIC DIVERSITY...
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netic diversity of L. multiflorum cultivars appears to be related to morphological variation. All
L. multiflorum cultivars analysed here by means of molecular markers are also clearly distinct
from ecotypes by extremely high values for generative traits (Chapter 3). Examination
of cp and mtDNA haplotypes shows that Bartissimo appears to be derived from Variamo
(the same cpDNA and mtDNA), Bartolini from Guliamo whereas a distinct mtDNA haplotype
in Atalja indicates different origin. However, each cultivar has specific haplotypes not present
in the other Lolium in addition to significantly higher frequency of several RAPD bands
(e.g., OPA02-4). Based on their morphological performance the introgressions from the other
closely related species e.g., from the genus Festuca is proposed (Chapter 3). The molecular
data seems to support this hypothesis. However, it must be emphasized that these interpretations
are preliminary and further organelle DNA data based on a wider primer and species
(e.g., Festuca) choice, will be needed to build up a definitive picture.
4.4.3. Phylogenetic relationships between L. multiflorum and L. perenne
The most striking results to emerge from the present work are high genetic similarities
between L. multiflorum and L. perenne more typically associated with conspecific populations.
Huge genetic identities are apparent in nuclear, chloroplast and mitochondrial genomes
(I ranged from 0.986 to 0.887). This is not unexpected because the high level of similarity
has been observed by the other authors as well (Bulińska-Radomska and Lester 1985; Loos
1993b; Bennett et al. 2002). However, most of these data were obtained by enzyme electrophoresis
and the authors believed that due to low resolution it would not be possible to make
more precise picture until advanced DNA methods would be available for forage grasses
(Charmet and Balfourier 1994). Although several DNA-based comparisons have been done
for Italian and perennial ryegrass (Stammers et al. 1995; Zielinski et al. 1997; Balfourier et al.
2000) none of these research are comparable with the present work both with reference to
the diversity of markers applied and plant material including cultivars and wild ecotypes. Another
important point to notice is the approach in which the same plant individuals have been
examined by all marker categories. This enables to compare the results obtained with different
methods on the same plant material. And the results are clear - the enzymatic data have
not been cheating - high similarity is observed at the DNA level irrespective of the marker
type used. Moreover, the gene identities obtained by different methods are very alike. Even
values based on insertional polymorphism that is thought to be highly differentiating, are well
ahead those for different species confirming the extensive gene flow between both species.
Considerations about the meaning of high similarity between L. multiflorum and L. perenne
inevitable give rise to the question how much genetic exchange disqualifies populations
from status as separate biological species. Biological species concept (BSC) perceives
species as populations between which the gene exchange is limited or prevented by reproductive
isolating mechanisms (Avise 2004). One difficulty of BSC involves the primacy of
reproductive barrier in demarcating species and thus, no arbitrary magnitude of molecular
genetic divergence can provide infallible metric to establish specific status. How, then, can
the molecular data inform about speciation of ryegrasses
One possibility is the estimation of genetic identity. The concept of genetic identity/distance
is fundamental to evolutionary studies. A genetic identity (I) between two sequences,