Evaluation of freezing tolerance of winter wheat (Triticum aestivum L.) under controlled conditions and in the field

Abstract

Freezing tolerance of winter wheat (Triticum aestivum L.) is one of the main factors governing winter survival. To avoid winterkill it is very important to choose freezing tolerant wheat genotypes. Experiments were carried out to evaluate freezing tolerance of winter wheat varieties and breeding lines under field and controlled conditions with cold acclimation and with no cold acclimation stage. Field experiments were done for two years during the winters of 2010–2011 and 2011–2012. The evaluation of winter hardiness was conducted in April of 2011 and 2012 by visual scoring on a 1–9 score basis (score 1 – all plants were killed, score 9 – all plants survived). Wheat genotypes under investigation experienced very different climatic conditions in the field during the two winters. Consequently, no correlation between winter hardiness scores of 2010–2011 and 2011–2012 winters was observed. Winter hardiness scores ranged from 1.0 (WW-8) to 7.6 (‘Zentos’) after 2010–2011 winter, whereas winter hardiness scores varied from 5.8 (WW-31) to 7.8 (‘Kovas DS’) after 2011–2012 winter. Freezing tolerance of winter wheat genotypes was also assessed in the controlled conditions by measuring chlorophyll fluorescence parameter Fv/Fm in leaves and percentage survival of plants after the freezing test. High correlation (r = 0.88, p < 0.01) between freezing test survival of non-acclimated wheat and Fv/Fm ratio showed that this method can speed up the selection for freezing tolerance by evaluating wheat genotypes immediately after the test. Results of our study showed low negative, but significant relationship (r = −0.41, p < 0.05) between 2010–2011 winter hardiness scores in the field and freezing test survival of non-acclimated plants in the laboratory experiment. Wheat genotypes that quickly lose winter hardiness have higher freezing tolerance without hardening stage. Our results support the hypothesis of two separate genetic systems of freezing tolerance in winter wheat which are determined by duration and rate of gene expression during cold acclimation.