Comparison of winter hardiness components in Fragaria L. accessions with different phenorhythmotypes in an artificial climate chamber

Background. Overwintering is a critical factor for strawberry cultivation in Russia. Those Fragaria L. spp. that grow in the Asian regions of Russia with an extreme continental climate, which have so far been little studied and are poorly involved in breeding practice, can serve as sources of winter hardiness. The objective of the study was to identify sources of high winter hardiness among the genus Fragaria L. under artificial climate conditions. Materials and methods. Experiments to assess winter hardiness in 17 Fragaria accessions were conducted in an artificial climate chamber in the winters of 2022/2023 and 2023/2024 according to the guidelines of the All-Russian Research Institute of Fruit Crop Breeding. Three components of winter hardiness were studied: early-winter frost resistance, the ability to maintain frost resistance after midwinter thaws, and the same ability at the end of the winter season. Results. Five accessions from the Asian part of Russia showed the highest average scores of resistance: 3 accessions of F. mandshurica Staudt, one of F. viridis (Duchesne) Weston, and cv. ‘Aleksandra’ developed at the Yakut Scientific Research Institute of Agriculture. The first four had a summergreen phenorhythmotype, i.e., they entered the winter with browned leaves. Those accessions withstood the low temperatures in the early winter and remained resistant to frosts after the midwinter thaw; however, some of them lost their post-thaw frost resistance by the end of the winter. For such accessions from regions with a clear seasonal temperature course, even a brief temperature increase means the onset of spring and causes rapid unhardening. Conclusion. The species F. mandshurica and F. viridis can make a valuable contribution to the enhancement of winter hardiness in strawberry cultivars.