Differential Response Of Wheat Cultivars To Components Of The Freezing Process In Saturated Soil

Winter wheat (Triticum aestivum L. em. Thell.) is sown in the autumn and harvested the following summer, and therefore must survive subfreezing temperatures for several months. Because of autumn rains and winter snows, the plants usually are subjected to these subfreezing temperatures while growing in saturated soil. As the plants freeze, they are subjected to freezing episodes that may vary in the cooling rate, the minimum temperature, the time at the minimum temperature, and the warming rate as the freezing episode ends. We investigated the impact of each of these freezing process components on the ability of 22 winter wheat cultivars to survive freezing in saturated soil using logistic regression and cluster analyses. The 22 cultivars formed three distinct groups when clustered on the odds ratios associated with the freezing process components. The distinctiveness of the three clusters indicated the cultivars within each cluster responded differently to the freezing process than cultivars in the other clusters. Some cultivars occurred in different clusters but had equal levels of freezing tolerance. We conclude the logistic regression/clustering analysis identified cultivars that differed in the mechanisms used to respond to freezing stress, and that equal levels of freezing tolerance can be attained through these different mechanisms. It may be possible to improve winterhardiness by genetically combining these disparate responses to the freezing process components.