AUTUMN FROST HARDENING OF ONE-YEAR-OLD PINUS-SYLVESTRIS (L) SEEDLINGS - EFFECT OF ORIGIN AND PARENT TREES

Greenhouse experiments were carried out to study the effects of geographical origin and parent trees on the autumn frost hardening of Pinus sylvestris (L.) seedlings after their first growing season. Artificial freezing with impedance measurements and visual needle injury classification were used to measure frost hardiness. There were significant differences in the timing of hardening between the forest populations. The origin of the male parents had a significant effect on freezing injury, indicating that early freeze testing can be used to evaluate the frost hardiness of seed orchard crops with pollen contamination. The hardiness of the offspring from controlled crosses was, however, lower than that of the stand controls. There were significant differences in frost hardiness between parent clones.