Logistic Regression Analysis of the Response of Winter Wheat to Components of Artificial Freezing Episodes.

Improvement of cold tolerance of winter wheat (Triticum aestivum L.) through breeding methods has been problematic. A better understanding of how individual wheat cultivars respond to components of the freezing process may provide new information that can be used to develop more cold tolerant cultivars. Data are presented indicating how various components of the freezing process impacted survival of the cultivars Eltan, Froid, Kestrel and Tiber. Response surface analysis and logistic regression equations suggested that cultivars Eltan and Froid used different mechanisms of responding to freezing stress than did Kestrel and Tiber. While Kestrel and Tiber appeared to use essentially the same mechanisms, plots of logistic regression analysis residuals suggested that Kestrel survived harsh freezing more efficiently that Tiber, but Tiber survived less harsh freezing that Kestrel. Two F2- derived F4 lines selected from the cross of Kestrel and Tiber were significantly more cold tolerant than Kestrel, the more hardy parent, under harsh freezing conditions. Analyzing the response of wheat cultivars to components of the freezing process provides clues as to which cultivars may use different mechanisms in responding to freezing stress. Developing logistic regression equations and examining their predictive capability in different populations appearing to use primarily the same mechanism provided evidence of differences in effectiveness of that mechanism in different genotypes. Hybridization of wheat lines using primarily the same mechanism but with differing effectiveness may result in the recovery of favorable allele combinations leading to enhanced freezing stress tolerance.