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6. DO ANY SPECIES BOUNDARIES...
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primers from a known sequence of the target genome and they can be readily transferred
between closely related species. For this reason STS markers may offer a reliable system
for mapping orthologous loci and aid in the alignment of genetic linkage maps (Taylor et al.
2001). Therefore a final objective of this part of studies was to map a number of STS markers
derived from Lolium and cereals sequences. Apart from them, a new approach was proposed
that employ primers complementary to conservative bacterial sequences as for example catalase-peroxidase
gene (KatG) or insertional elements. Such primers have proved to amplify
reproducible polymorphism in many plant taxa and are useful as species specific markers
(Zielinski and Polok 2005). When two species have different banding patterns revealed by
bacterial specific primers, the encoding sequences can be mapped in interspecific crosses
what can further inform about genomic regions responsible for species divergence. From one
side, mapping of markers generated by bacterial specific primers would confirm our observations
that descendants of bacterial genes do exist in plant nuclear genome, and from another
it would support the utility of this approach for evolutionary studies in plants.
Second, RFLP based maps tend to focus on unique sequences and probes. When they
map to more than one location they are very often discarded from analyses as artefacts.
Such a strategy entails inevitable to overestimating the level of synteny between closely
related species (Bennetzen 2000). Much of the differences between genomes of closely
related species are attributable to repetitive sequences. The first RFLP map generated for
sorghum disclosed large conserved genic regions in comparison with maize. In contrast, the
interspersed regions were highly diverged (Bennetzen and Freeling 1997). This dynamism of
intergenic regions results from rapid turnover among transposable elements. Linkage maps
based on transposons provide insight into the pattern of genetic incompatibilities between
closely related taxa including I. fulva and I. brevicaulis (Bouck et al. 2005). Unfortunately, up
to date the transposon approach has been rarely used in mapping studies of cereals, and
none insertional polymorphism has been map in Lolium yet. This is the first attempt to map
insertion sites related with both DNA and retrotransposons in L. multiflorum and L. perenne.
6.2. MATERIAL AND METHODS
6.2.1. Magnitude of marker distortions in intra and interspecific crosses
Plant material
To select the most polymorphic population for mapping studies and to estimate the
marker distortions at intra- and interspecific level four F 2
families were compared. The detailed
description of these families, crossing experiments and plant development are given
in Annex 13.1. Shortly, two populations, namely HU5 x BO2 and BR3 x NZ15 were derived
from interspecific crosses. The former originated from a cross between a Hungarian ecotype
of L. perenne and the cultivar of L. multiflorum, Bartissimo. The latter was derived from the
cultivar of L. multiflorum, Bartolini and a L. perenne ecotype from New Zealand. Moreover
two intraspecific populations were included in the analysis. The population coded VA7 x
AS17 originated from L. multiflorum and was derived from a cross between an Italian ecotype,
Variamo and the cultivar, Asso. The population coded KY20 x BB6 originated from