Influence of Vernalization and Photoperiod Responses on Cold Hardiness in Winter Cereals

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Abstract
An understanding of the genetic regulation of low‐temperature (LT) tolerance is a prerequisite for the development of cold tolerant cultivars for high stress regions. Vernalization requirement in winter habit cereals and photoperiod responsiveness in spring habit cereals has been shown to influence expression of the LT tolerance genes. The objective of the present study was to determine the influence of photoperiod response on expression of LT tolerance genes in vernalization requiring winter habit cultivars Norstar and Warrior wheat (Triticum aestivum L. em. Thell) and Kold barley (Hordeum vulgare L.). These cultivars were subjected to 8‐h‐short day (SD) and 20‐h‐long day (LD) photoperiods at cold acclimating temperature (4°C) over a period of 0 to 98 d. Final leaf number (FLN) was determined at intervals throughout the acclimation period to measure vernalization status. Photoperiod sensitivity did not affect vernalization as both SD and LD plants reached vernalization saturation at the same time. However, a significant increase in leaf number and delayed double ridge formation between 49 and 98 d under 4°C SD non‐inductive flowering condition relative to the LD treatments indicated that SD delayed phenological development. Low‐temperature tolerance gene expression as measured by LT50 was influenced before the signal for floral transition as indicated by FLN measurements. Photoperiodic response of SD sensitive winter barley and wheat cultivars was reflected in the level of expression of LT tolerance beginning in the early stages of vernalization and plant development. Subsequent LT acclimation continued for a longer time and to colder temperatures under SD compared to LD. These results support the hypothesis that vernalization and photoperiod responses regulate the expression of LT tolerance genes through their influence on the rate of plant development.