Photosynthetic acclimation to cold as a potential physiological marker of winter barley freezing tolerance assessed under variable winter environment

Winter-hardiness is a complex trait limiting cultivation of winter barley (Hordeum vulgare ssp. vulgare) with respect to the regions of temperate climate. In the present studies, we verified whether inexpensive and fast physiological markers characterizing photosynthetic acclimation to cold may provide robust characteristics of winter barley genotypes for improved frost resistance. Freezing tolerance of 28 winter barley varieties and advanced breeding lines were tested for three winters in field-laboratory experiment and under fully controlled conditions. To increase the environmental variability of freezing tolerance, a part of the plants were also de-acclimated under semi-controlled conditions and re-acclimated in laboratory before freezing tests. After controlled cold acclimation, apparent quantum yield of photosystem II (F-v/F-m) as well as photochemical (q(P)) and non-photochemical (NPQ) coefficients of chlorophyll fluorescence quenching were studied. Field-laboratory method assessment of freezing tolerance gives distinct and even opposite results in subsequent years. Also de-acclimation interacted with growth conditions in the field, giving different rankings of genotypes each year. The results obtained suggest that high level of freezing tolerance measured in laboratory, which is connected with photosynthetic acclimation to cold may be not sufficient for the expression of field resistance, especially when winter conditions are not favourable for cold acclimation.