Diversity in the Response to Low Temperature in Representative Barley Genotypes Cultivated in Europe

Barley (Hordeum vulgare L.) production in many regions is constrained by low temperatures. Numerous screening methods have been proposed for studies of freezing tolerance (FT) and winter hardiness (WH). Here, we compared the response to low temperature of 54 barley genotypes released in Europe. Major components of WH were analyzed in field and growth chamber experiments under different hardening and freezing conditions. Phenotype screening of freezing injury (lethal temperature for 50% of the plants [LT50], plant survival, and chlorophyll fluorescence) and indirect evaluations (molecular-marker-based analysis of vernalization requirement) were used. The maximum quantum yield of the photosystem II photochemistry measured as the variable (F-v) to maximal (F m) fluorescence ratio (F-v:F-m) analysis was confirmed as a reliable method of screening genetic diversity for FT in plants at early growth stages. Variability for FT was also found after shorter acclimation at optimal (3/1 degrees C day/night) or suboptimal (12/7 degrees C day/night) hardening temperatures. High levels of FT and WH were found in both winter and facultative growth habits. Facultative genotypes were more responsive to early hardening than spring or winter types. Some of them coped best with frost in both laboratory and field experiments. The most tolerant winter genotypes coped best with prolonged exposure to low temperature in the field experiments. A conservative estimation of the role of FT in WH implies that at least 50% of WH was associated with the level of FT. A combined analysis using physiological and molecular tools is proposed for phenotyping WH in large populations.