Survival analysis of freezing stress in the North American native perennial flax, Linum lewisii Pursh

The expansive range of Lewis flax (Linum lewisii Pursh.), an herbaceous perennial, exposes the species to a diversity of climatic conditions. As interest in the domestication and adoption of perennial crop alternatives grows and interest in this species for natural area restoration continues, the assurance of a commercial plant variety’s ability to endure the full range of possible climatic extremes is paramount. This study examines the freezing tolerance of a geographically representative sampling of 44 Lewis flax accessions at winter temperature extremes experienced in the northern Great Plains of the United States. Survival analysis models were adapted to include temperature exposure, in replacement of ordinal time typically used in such models, to produce statistics evaluating reactions to extreme temperatures that Lewis flax would encounter in our field environments. Our results revealed Lewis flax is more freezing tolerant than previously reported, and revealed four accessions with significantly superior genetic freezing tolerance than the released ‘Maple Grove’ cultivar. Furthermore, regrowth analyses indicate variation among accessions not associated with survival, which could lead to improving regrowth rate and survival simultaneously. These findings and their methodology expand the understanding of Lewis flax adaptation for winter hardiness and offer an efficient, new model that can be used to evaluate freezing tolerance at ordinal temperatures without requiring extensive prior physiological knowledge for a species.