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8. MOLECULAR PHYLOGENY OF THE GENUS LOLIUM
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that it has hardly been included in such analyses. Perhaps the underlying reason is the
unclear position of this species that can spoil each dendrogram owing to disagreement with
common classifications. For instance, the placement of L. loliaceum with L. rigidum in the ITS
based dendrograms has led Gaut et al. (2000) to the conclusion that ITS does not provide
consistent insights into the phylogenetic placement of this species. The first data that the origin
of L. loliaceum may be different from the remaining autogamous species have come from
AFLP studies (Polok et al. 2006). The placement of L. loliaceum together with multiflorum,
perenne and L. rigidum demonstrates clearly, that it evolved within a group of out-pollinated
species followed by several point mutations responsible for self-fertility. The results from the
genus Lycopersicon indicates that the autogamy is controlled by at least five tightly linked
genes controlling style length, stamen length and anther dehiscence. The clusters of genes
associated with various aspects of transition from outcrossing to self-pollination probably
exist in many plants and represent an ancient co-adapted gene complex controlling mating
behaviour. A single mutation in se2.1 gene on chromosome 1 of tomato results in more
recessed stigmas and it is a major change accompanied the evolution from allogamous to
autogamous species (Chen and Tanksley 2004).
Various molecular methods employed to assess phylogenetic relationships within the
genus Lolium in the current studies unequivocally confirm the close affinity of L. loliaceum
to out-pollinated species. In all dendrograms it consequently groups with multiflorum, perenne
and L. rigidum. It has also similar cpDNA and mtDNA haplotypes, as well as the
structure of the LOLMTI mitochondrial gene and the LOLPISO5A gene encoding pollen
allergen. If L. loliaceum is included into the out-pollinated section than the genetic similarities
between two clades drop down thereby, confirming that they are distinct lineages. For
example, the genetic similarity between two “molecular” clades is twofold lower as estimated
by AFLP and SSR and around 20-30% lower as indicated by the remaining molecular
marker categories than for comparisons between autogamous vs. allogamous sections
(Table 8.4).
Hence, the conclusion emerging from the current data is clear - the genus Lolium
should be divided into two clades, the first consisted from L. persicum, L. remotum
and L. temulentum, whereas the second from L. loliaceum, L. perenne ssp. multiflorum,
L. perenne ssp. perenne and L. rigidum. These two clades as discussed earlier likely diverged
independently from the common ancestor similar to the present Schedonorus genus.
Under the above hypothesis, naming the two clades as groups of self-pollinated and outpollinated
species can not be held any longer for the reason that self-pollinated species are in
both groups. It would be reasonably to assign both clades either after the progenitor or after
the most common representative e.g., Temulentum clade for the first one, and Perenne clade
for another. The time of divergence of the Temulentum clade from a common ancestor can
be estimated as 2.5 MYA using molecular clock based on Charmet et al. (1997) calculations
or as 2.7 MYA using t=D/2α transformation and 2 x 10 -7 as the substitution rate. The Perenne
clade split from Schedonorus (F. pratensis) about 2.35 MYA. Such scenario means that the
ability to self-pollination arose independently in both clades as it has already been suggested
using AFLP profiles (Polok et al. 2006).