© 1994 Heron Publishing—Victoria, Canada
Cold acclimation in eucalypt hybrids
M. H. Almeida (1), M. M. Chaves (2) and J. C. Silva (3)
1. Departamento Eng. Florestal, Instituto Superior de Agronomia, 1399 Lisboa Codex, Portugal / 2. Department of Botany, Instituto Superior de Agronomia, 1399 Lisboa Codex, Portugal / 3. Royal Veterinary and Agricultural University, Arboretum, DK-2970 Hørsholm, Denmark / Received October 8, 1993
Summary
We evaluated cold resistance and the capacity for cold acclimation of different Eucalyptus genotypes. Seedlings of half-sib families of E. globulus and hybrids E. gunnii × globulus, E. viminalis × globulus and E. cypellocarpa × globulus were exposed daily for 56 days to a 9-h photoperiod at 14.7 °C, followed by 15 h in a dark cold room maintained at 2.5 °C
with the root system maintained at 8 °C to cold harden the seedlings. Unhardened seedlings were maintained at about 16 °C
during the dark period. Cold acclimation occurred in all families with decreases in the temperature causing 50% mortality
(LT50) of between 1.5 and 3 °C. Both hardened and unhardened plants of hybrid families were more cold tolerant than E. globulus. A significant correlation between LT50 and leaf osmotic pressure was observed; the increase in osmotic pressure in hardened plants was predominantly a result of
an increase in the concentration of soluble sugars. Exotherm peaks were similar in hardened and unhardened plants. These results
indicate that cold hardening increased the ability of eucalypts to endure extracellular ice formation. The maintenance of
photosynthetic capacity in cold-hardened plants may also play a role in their response to freezing.
Keywords:
cold hardening, Eucalyptus, leaf water potential, osmotic pressure, photosynthetic capacity, soluble sugars.
