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4. GENETIC DIVERSITY...
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mean number of bands per a site were higher in L. multiflorum than in L. perenne, especially
for Tpo1 and Lolcopia1. These two parameters did not differ between species in the case of
the third transposon, Lolcopia2.
In Italian ryegrass, the results showed the comparable insertional polymorphism
level for Tpo1 (82%) and Lolcopia1 (83%) and lower for Lolcopia2 (76%). By contrary, in
L. perenne this last transposon showed almost equal level of polymorphism to Tpo1 (72 and
70%, respectively) while the lowest value was given by Lolcopia1 (59%). The differences
in percentage may indicate that each transposon has a characteristic level of transposition
within Italian and perennial ryegrass. Inspection of cultivars and ecotypes of both species
confirmed higher number of insertion sites in L. multiflorum. In both species higher level of
polymorphism was observed in ecotypes. This is in opposite to RAPD and ISJ results but
not surprising as cultivars have been generally derived from a narrow gene pool. However,
this relationship was not so obvious when taking into account the mean number of bands per
a site because they did not differ between ecotypes and cultivars within a species.
There was a great amount of band sharing between both species (Figure 4.4A). No
differences were observed in several bands of the same mobility in both species after the
elution from the polyacrylamide gel and their re-amplification (Figure 4.4B). Despite the high
resolution of SSAP and a great number of bands identified, species specific markers could be
scarcely found and they constituted only 1.9% (12 bands) of all identified bands. Two of employed
transposons had unique insertion sites for each species. The DNA transposon, Tpo1,
revealed one site in each species (Figure 4.5) and the retrotransposon Lolcopia1, five sites in
L. multiflorum and three in L. perenne (Figure 4.6). The other retrotransposon, Lolcopia2 was
found in three specific sites only in L. perenne (Figure 4.7). Moreover, there were significant
differences in transposon frequency between species for about 3% of insertion sites.
4.3.2. Genetic diversity of L. multiflorum and L. perenne
The value of genetic variability in L. multiflorum and L. perenne was almost identical
and the majority of Nei’s genetic parameters did not differ between them (Table 4.5). Both
species had relatively large total gene diversity (H T
) that ranged from 0.253 to 0.344 in Italian
ryegrass and from 0.202 to 0.340 in perennial ryegrass. About 40-60% of this variation
was distributed between populations as estimated from G ST
. Also the D ST
value informing
about the among-population gene diversity was usually higher than H s
informing about the
within-population gene diversity. The significant deviation from zero of the fixation index (F IT
)
was observed in both species for the majority of marker systems applied. The differences
between L. multiflorum and L. perenne were displayed only in few cases. The former had
higher transposon diversity (higher H T
, H S
and G ST
for Tpo1 and Lolcopia1) while in the latter
splice junctions and cpDNA were more diverged (higher values of D ST
and G ST
).