Frost tolerance and hardening capacity during the germination and early developmental stages of four white spruce (Picea glauca) provenances

Abstract

Frost tolerance during the germination stages of four white spruce (Picea glauca (Moench) Voss) provenances (between 45°37' and 50°17'N) was studied at four different developmental stages (imbibed seed, radicle, cotyledon, and young seedling), and their hardening capacity was determined for the latter three stages. Hardening capacity was examined by submitting radicle-stage germinants to two temperature-photoperiod treatments (20:15°C - 16-h photoperiod or 5:5°C - 8 h) for 14 days and by submitting cotyledon and young seedling stage germinants to four treatments (20:15°C - 16 h; 20:15°C - 8 h; 5:5°C - 16 h; 5:5°C - 8 h). Frost tolerance was determined immediately after these treatments. Latitude of origin showed no clear pattern with respect to either frost tolerance or hardening capacity at any of the developmental stages. Imbibed seeds had the greatest degree of frost tolerance. With the exception of the most northern provenance, radicle-stage germinants did not respond to a 5:5°C day:night temperature and 8-h photoperiod hardening treatment. A low-temperature treatment of 5:5°C increased the frost tolerance of cotyledon and young seedling stage germinants, while their response to a shortened photoperiod (8 h) was quite variable. However, an 8-h photoperiod did enhance the effect of the low-temperature treatment at the young-seedling stage. Thus, the timing of germination in the field appears to be an important factor in the ability of germinants to tolerate freezing stress.Key words: germination stage, frost tolerance, hardening capacity, photoperiod, temperature.