Three-year screening for cold hardiness of garden roses

Garden roses have a high ornamental and economic value. They are usually produced in one climatic zone, then sold to another climatic zone. Cold stress can severely inhibit their regrowth and ornamental quality. Knowledge of cold hardiness of specific genotypes is therefore necessary before commercialization to colder regions. 17 roses with diverse genetic backgrounds and belonging to different USDA (United States Department of Agriculture) plant hardiness zones were chosen for a three-year cold hardiness screening based on the index of injury method. Stems were sampled on 3rd February 2015, 20th January 2016 and 23rd January 2017 after a freezing period of six successive days. Cold hardiness levels were determined by controlled freezing to −20 °C. Genotypes with the highest and lowest levels of cold hardiness were confirmed during these three years. Soluble carbohydrates were analyzed. The results showed that both sucrose and oligosaccharides contributed to cold hardiness in the studied roses. When genotypes with known cold hardiness are included in screening programs, this approach can lead to rapid screening of new rose genotypes.