Sammendrag
In a ×Festulolium population (FuRs0357) of parental origin Lolium perenne × Festuca
pratensis, selection of freezing tolerance by freezing tests on whole plants (FT) and
chlorophyll a (Chl-a) fluorimetry on frozen detached leaves (CF) was assessed in high
and low directions during two cycles of selection. The original population went through
two cycles of random mating. All selections and non-selected intercrossed generations
of the original population were established in field trials at a coastal site and a continental
site in Norway. At the coastal site, analyses of Chl-a fluorimetry parameters and leaf
growth on individual plants in autumn and winter hardiness observed in field plots
in spring showed that the first-generation selections for high freezing tolerance were
associated with winter hardiness and early growth cessation. The second-generation
FT-selections for high freezing tolerance were also associated with winter hardiness,
whereas the CF-high selections diverged toward high photosynthetic activity. Both
low selections were correlated with high photosynthetic activity. There were smaller
variations between generations in unselected generations of the original population.
Low accumulated leaf growth and early growth cessation were observed in the secondgeneration
FT-selection for high freezing tolerance, whereas high normalized difference
vegetation index (NDVI) were seen in Chl-a selections. Both selection methods
distinguished diverging selections with significantly different high and low freezing
tolerance, but selection efficiency was comparable only for the first selection cycle.
Moreover, due to mixed ploidy level in the original population, selection by FT and CF
generated diploid and tetraploid plants, respectively, which intensified the response of
selection, particularly in the diploid selections. Total dry matter yield (DMY) (mean of three
annual cuts for 3 years) of the FT-high selections was lower than for the CF-selections. At
coastal sites, selection intensity using freezing tests on whole plants should be adapted
to actual climate conditions, to obtain genotypes that balance photosynthetic activity
during autumn and good winter hardiness, making them persistent and high yielding.
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