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3. MORPHOLOGICAL VARIATION...
different environments in addition to the lack of reproductive barriers - all these argue for taking
them as a single entity.
The history of crops has proved that many of more dramatic differences in plant morphology
are due to differences in one, or just a few genes and many have been induced by
mutagenic treatment. Some of these mutants fall outside the accepted morphological limits
not merely of the species, but of the genus. However, the classification keys rarely take them
into account that resulted in a kind of “unnatural” classification. Crosses between these different
forms readily give rise to true-breeding intermedium forms as it is observed in barley
after crossing six-rowed with two-rowed cultivars or in Lolium as a result of hybridization
between L. multiflorum and L. perenne. The latter is often classified as Lolium x hybridum.
As such, it is intermediate in many traits; it is less winter hardy but higher yielding than perennial
ryegrass. Regularly producing new species by crossing different forms seems absurd. In
barley, for example, following a re-classification all mutants, ecotypes and cultivated forms
were included in a single entity Hordeum vulgare (Briggs 1978). Such approach is also presented
for L. multiflorum and L. perenne in the Integrated Taxonomic System of the USA
(2007). This seems especially justified by human activities, which have probably caused the
observed diversification of both taxa. This conclusion is supported by the distinction of L. multiflorum
cultivars from the remaining populations. They are characterized by extremely high
values for generative characters. Italian ryegrass is primary used as an annual forage crop
to provide high quality grazing for dairy cattle. Therefore, it should be easy to establish, grow
rapidly and produce high yields through the summer (Cosgrove 1999). The demand for improvements
through breeding programmes directed to rapid grow, high quality forage and die
after heading has resulted in lower winter hardiness, greater number of heading plants in the
1st year, longer spikes and greater number of spikelets in L. multiflorum cultivars in comparison
with ecotypes. Most importantly, these predicted increases may be small but could pose
a serious challenge to taxonomists. Cultivars represent the transgressive segregation and as
such they fall easily outside the species mean. If selection of perennial ryegrass is directed
into opposite direction i.e., to more persistent, later flowering cultivars, the separation of
L. multiflorum and L. perenne may be produced artificially. This scenario seems plausible as
confirmed by the lack of differences between both species at the ecotype level.
Several authors argued that breeding activities have increased the level of hybridization
between L. multiflorum and L. perenne and resulted in huge amount of introgressive forms
in nature (Bennett et al. 2002). This further will cause the morphological unification of both
species. However, the results from this study do not support this view. Taking into account
higher similarity between ecotypes of both species in comparison with cultivars, it can be
speculated that differences between them have been produced recently by genetic manipulations
during breeding programmes especially in L. multiflorum. It should be noted that in
the most distinct cultivars some unusual characters were observed - thick stems, very wide,
stiff and rough leaves and branched spikes. The introgression from Festuca species can not
be therefore, excluded. Introgression is a backcrossing procedure, which allows a limited
number of alien genes to be introduced from a donor species into the reconstituted genome
of the recurrent species by recombination and selection. The diversity of demands on grasslands
agriculture has led to increasing effort in widening the Lolium gene pool through the
exploitation of the close relationship between Lolium and Festuca. Although less digestible