increase tolerance to adverse environmental factors into the
genome of plants susceptible to environmental stress. High
hopes are laid onto intraspecies and interspecies hybrids,
which combine advantageous features of the parental species
in their genome. They are a valuable source of variation
for increasing resistance to abiotic and biotic stresses. One
of such hybrids is Festulolium braunii, the effect of the
crossing of L. multiflorum and F. pratensis (Sulinowski
1968). Parent species easily intersect and their chromosomes
have sufficient homology, so they can be conjugated
and recombined in the hybrids. The works on the complex
hybrids of Lolium–Festuca have been conducted for many
years in various research centers in Poland (Zwierzykowski
et al. 1998, 1999) and in Europe (Fojtik and Vacek 1983;
Ghesquie`re et al. 1996; Jadas-Hecart et al. 1991; Levis et al.
1973; Netzband 1990; Thomas and Humphreys 1991).
Breeding plants resistant to soil drought are very complex
because the genes responsible for the reaction of
plants to water stress are located in different chromosomes
and their activity is sometimes coupled with the influence
of other genes. In addition, the final effect is strongly
modified by environmental conditions and depends on the
plant development stage (Dziadczyk 2002). According to
Maximov (cited by Gej 1961), each plant organ is the most
sensitive to water shortage in the most intense phenophase.
This is a critical period when the plant is extremely sensitive
to the stress factor. In the case of forage grasses, this
period occurs at the end of vegetative development and the
beginning of the creation of generative organs (Staniak
2013). The studies of Jurek (1994) showed that the course
of phenomena related to the effects of water deficit on the
growth and development of the perennial plants, such as
grasses, should be tested taking into account the time
factor, as young plants (in the first year of utilization) respond
differently to older plants (in the third year of utilization)
(Table 3). The own studies using different
cultivars of D. glomerata, F. pratensis, F. braunii, and L.
multiflorum also showed that young plants in the first year
of vegetation were less responsive to drought (yields lower
by an average of 35 %) than older plants in the second and
third year of use (yields lower by an average of 49 %)
(Staniak 2013).