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Title: Exposure to subfreezing temperature and a freeze-thaw cycle affect freezing tolerance of winter wheat in saturated soil

Author
item Skinner, Daniel
item Bellinger, Brian

Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/12/2010
Publication Date: 6/15/2010
Citation: Skinner, D.Z., Bellinger, B.S. 2010. Exposure to subfreezing temperature and a freeze-thaw cycle affect freezing tolerance of winter wheat in saturated soil. Plant and Soil. 332(1):289.

Interpretive Summary: Winter wheat plants are seeded in the fall and harvested the following summer and therefore must have winterhardiness, an ability to withstand several exposures to subfreezing temperatures. In this study, 24 winter wheat cultivars were evaluated for their ability to withstand freezing to potentially damaging temperatures after one of three pre-freezing treatments; incubation at -3C for six hours, or 16 hours, Or a mild, 24 hour freeze-thaw cycle followed by incubation at -3C for 16 hours. The mild freeze-thaw treatment resulted in improved freezing tolerance especially apparent under harsher freezing conditions. The six-hour pre-freezing treatment resulted in very poor freezing tolerance; the 16 hour pre-freezing treatment resulted in intermediate freezing tolerance. The ability of the cultivars to withstand freezing was not consistent among the pre-freezing treatments, indicating variation in the ability to withstand the different kinds of stress imposed by the three treatments. It should be possible to improve winter hardiness by genetically combining the ability to survive each of the kinds of stress brought about by the variation in the freezing treatments.

Technical Abstract: Winter wheat is sown in the autumn and harvested the following summer, necessitating the ability to survive subfreezing temperatures for several months. Autumn months in wheat–growing regions typically experience significant rainfall and several days or weeks of mild subfreezing temperatures at night, followed by above-freezing temperatures in the day. Hence, the wheat plants usually are first exposed to potentially damaging subfreezing temperatures when they have high moisture content, are growing in very wet soil, and have been exposed to freeze/thaw cycles for a period of time. These conditions are conducive to freezing stresses and plant responses that are different from those that occur under lower moisture conditions without freeze/thaw cycles. This study was conducted to investigate the impact of mild subfreezing temperature and a freeze/thaw cycle on the ability of 24 winter wheat cultivars to tolerate freezing in saturated soil. Seedlings that had been acclimated at +4°C for 5 weeks in saturated soil were frozen to potentially damaging temperatures under three treatment conditions: (1) without any subzero pre-freezing treatment; (2) with a 16-hour period at ¬–3°C prior to freezing to potentially damaging temperatures; and (3) with a freeze/thaw cycle of –3°C for 24 hours followed by +4°C for 24 hours, followed by a 16-hour period at ¬–3°C prior to freezing to potentially damaging temperatures. Plants that had been exposed to the freeze/thaw cycle survived significantly more frequently than plants frozen under the other two treatments. Plants that had been exposed to 16 hours at -3° (without the freeze/thaw cycle) before freezing to potentially damaging temperatures survived significantly more frequently than plants that were frozen to potentially damaging temperatures without a subzero pre-freezing treatment. These results indicated that cold-acclimated wheat plants actively adapt to freezing stress while exposed to mild subfreezing temperatures, and further adapt when allowed to thaw at +4° C for 24 hours. This phenomenon was observed in most of the 24 cultivars examined, but freezing tolerance of several cultivars was not improved by the freeze/thaw cycle, indicating variation in the ability to effectively respond to mild subfreezing temperatures. The cultivar Norstar had the greatest survival of the 24 cultivars when frozen with either of the subzero pre-freezing treatments, but the cultivars Wanser and Froid survived significantly better than Norstar when frozen without any subzero pre-freezing treatment. We suggest it may be possible to improve winterhardiness of wheat grown in saturated soil by combining the ability to effectively respond to mild subzero pre-freezing temperatures with a greater ability to withstand freezing to damaging temperatures without a subzero pre-freezing exposure.