SEASONAL COLD-ACCLIMATION PATTERNS OF `AUTUMN JOY' AND `BRILLIANT' SEDUM

Abstract

Electrolyte leakage and regrowth tests were performed in successive months from September to January to determine cold hardiness of container-grown Sedum spectabile Xtelephium L. `Autumn Joy' and Sedum spectabile Boreau. `Brilliant' plants exposed to natural temperature and photoperiod. Plant crowns were subjected to 0, -3, -6, -9, -12, -15, -18, -21, -24, or -27C in a programmable freezer. Regrowth tests were performed on whole crowns and electrolyte leakage determinations were made on excised tuberous root and crown tissues. Regrowth data indicate both cultivars had killing temperatures of -3C at the September test date, prior to the onset of cold-acclimation. By October, the killing temperature for `Autumn Joy' had dramatically decreased to -12C, with more gradual acclimation occurring thereafter. The killing temperature for `Brilliant' decreased from -3C in October to -18C in November. In this study, maximum hardiness was achieved on the January test date with killing temperatures of -24 and -21C for `Autumn Joy' and `Brilliant', respectively. Correlation coefficients suggest the electrolyte leakage procedure was able to reliably estimate `Autumn Joy' cold hardiness at each test date, but was less accurate for `Brilliant'. Regrowth tests are tedious and qualitative, but remain reliable predictors of plant viability. Electrolyte leakage tests were successful in estimating survival potential of plants exposed to freezing temperatures using either excised crown or tuberous root tissue.