Temperature is an important driver for cold acclimation in garden roses

Low non-freezing temperatures and short days are two main environmental factors that can independently or collectively initiate cold acclimation in temperate perennials. Freezing temperatures are required for the full development of mid-winter cold hardiness. In the present study, six rose genotypes with different cold hardiness levels were selected to investigate cold acclimation under both long and short photoperiods to reveal the role of temperature and day length on cold acclimation of roses. A five-week short-day treatment at 20/18 ? did not induce cold acclimation in any of the genotypes. Cold hardiness levels (LT50 values) increased significantly at low non-freezing temperatures (2 ?) and freezing temperatures (-5 ?) irrespective of the photoperiod for all genotypes. The more cold-hardy 'Dagmar Hastrup' and 'John Cabot' responded strongly, achieving lower LT50 values under low non-freezing temperatures. Low non-freezing temperatures/freezing temperatures but not short days promoted the degradation of starch and the accumulation in sucrose, hexoses, and raffinose. Short days alone induced RhDHN5 in 'Yesterday', 'Abraham Darby', and Rosa wichurana. However, the expression of RhDHN5 was up-regulated significantly by low non-freezing temperatures in all genotypes. The up-regulation of RhBAM3 by lowering the temperature (low non-freezing temperatures and/or freezing temperatures) is genotype-independent. Freezing temperatures had a prominent role in accelerating the expression of RhGolS2 in all genotypes. The up-regulation of RhRS2 and RhRS6 is mainly induced by low non-freezing temperatures and freezing temperatures, respectively, but transcript levels for both were less pronounced than those for RhGolS2. Stem dehydration during cold acclimation was only found for 'Chandos Beauty' under long days and R. wichurana under short day length. R. wichurana was insufficiently acclimated to withstand freezing temperatures under short day length. This study clearly shows that the main factors triggering cold acclimation in roses in 5 rose genotypes are low non-freezing temperatures or freezing temperatures, but a synergistic effect of short photoperiod and low non-freezing temperatures was found for R. wichurana.

Automated summary

Low temperatures and short photoperiods are the main environmental factors that trigger cold acclimation in roses, with different effects on different genotypes.