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8. MOLECULAR PHYLOGENY OF THE GENUS LOLIUM
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Clade II - PERENNE
The clade Perenne consists of four taxa, allogamous L. perenne ssp. multiflorum,
L. perenne ssp. perenne, L. rigidum and autogamous L. loliaceum. This clade seems to be
less differentiated at least taking into account crossability between species. Therefore, the
species delimitation has been a subject of a great contention for many years. The most controversies
have been related with species status of perenne and multiflorum. The results presented
throughout all chapters demonstrate clearly, that there is no any reproductive barrier
between them and they can not be regarded as biological species. Furthermore, historical
data (Beddows 1953) indicate that multiflorum is a domesticated form of perenne and the
domestication process started in Italy before the twelfth century. The location of QTLs associated
with the domestication syndrome is the other evidence confirming the historical records.
The questions to be solved involve the diversification of L. rigidum, L. loliaceum and L. perenne
from the common ancestor.
From the majority of dendrograms and additional considerations it is plausible that the
earliest evidence of divergence within this clade is related to L. rigidum. Somehow different
cpDNA and pollen allergen genes seem to support this view. The average I value equal to
0.563 between L. rigidum and the remaining species within the Perenne clade points at the
presence of reproductive barriers. However, this prediction weakens considerably when data
about full crossability between L. rigidum and the remaining species are taken into account
(Loos 1993a; Bennet et al. 2002). Consequently, some authors classify L. perenne ssp. multiflorum,
L. perenne ssp. perenne and L. rigidum as a single entity (Bulińska-Radomska and
Lester 1985). On the other hand, there are hardly any documented data about the crossability
of L. rigidum with the others and it remains to be established in experimental crosses. Indirect
evidences come from hybrids between L. loliaceum x L. rigidum that are all male sterile (Jenkin
1959). Nevertheless, the present molecular data predict that such hybrids will be at least
partially sterile. With regard to the likely time when L. rigidum diverged from the rest of the
Perenne clade species, it can be estimated on about 1.4 MYA.
The divergence between L. loliaceum and L. perenne can be postulated to be about 1.2
MYA. It presumably followed several spontaneous mutations leading to self-pollination. In
contrast to the self-pollination within the Temulentum clade, its birth in L. loliaceum was not
connected with agriculture. Considering the value of genetic identity between L. loliaceum
and L. perenne (I=0.624), they must have split only recently but the reproductive barriers must
exist owing to low seed setting in hybrids between L. perenne ssp. perenne x L. loliaceum.
A cautionary point should be made that low copy sequences group L. loliaceum more closely
to multiflorum suggesting their common origin. The distribution of AluI restriction sites in the
LOLMTI mitochondrial gene and the LOLPISO5A gene encoding pollen allergen, RsaI and
TaqI sites in the latter also point at the closest affinity of L. loliaceum to L. multiflorum. On
the other hand, such origin seems unlikely from at least two reasons. First, multiflorum and
perenne have nearly the same genome and indeed, the former is a domesticated form of the
latter. Under this hypothesis L. loliaceum would have been derived only recently from already
selected forms as another domesticated form. However, in that case it should be much more
similar to both multiflorum and perenne and the reproductive barrier would be rather excluded.
Second, both mtDNA and allergens tend to cause bias in phylogenetic analyses. Therefore,