Cold hardiness is the primary factor restricting the northward expansion of winter wheat (Tritlcum aestivum L. em. Thell.) in the Great Plains area of North America. Several factors, including the absence of a simple, reproducible method of screening, high experimental error associated with field trials, limited genetic variability, and difficulties in combining a high level of cold hardiness with other desirable characteristics have all been responsible for the lack of progress in breeding for this character. To assess the extent of these limitations 61 field trials were grown in Saskatchewan, Canada, from 1972 to 1977. Included in these trials were 43 winter wheat cultivars of diverse origin.

The Field Survival Index (FSI), based on a modified procedure for determining relative winter hardiness of cultivars in field trials, was developed. This method of estimating cuitivar winterhardiness potential reduces the experimental error associated with field trials, alleviates the difficulties arising from the absence of partial winteridll for a few cultivars in each trial, and allows for the pooling of results from different trials.

A wide ranges in FSI's was observed for the cultivars considered. These ratings suggest that most successful winter wheat cultivars have only marginally greater winterhardiness than the minimum required for the sea in which they are grown. As in the past, cultivars with USSR genotypes in their pedigrees had the highest winter terhardiness potential.