FROST TOLERANCE AND HARDENING CAPACITY DURING THE GERMINATION AND EARLY DEVELOPMENTAL STAGES OF 4 WHITE SPRUCE (PICEA-GLAUCA) PROVENANCES

Frost tolerance during the germination stages of four white spruce (Pi cea glauca (Moench) Voss) provenances (between 45 degrees 37' and 50 d egrees 17'N) was studied at four different developmental stages (imbib ed seed, radicle, cotyledon, and young seedling), and their hardening capacity was determined for the latter three stages. Hardening capacit y was examined by submitting radicle-stage germinants to two temperatu re-photoperiod treatments (20:15 degrees C - 16-h photoperiod or 5:5 d egrees C-8 h) for 14 days and by submitting cotyledon and young seedli ng stage germinants to four treatments (20:15 degrees C - 16 h; 20:15 degrees C - 8 h; 5:5 degrees C - 16 h; 5:5 degrees C -8 h). Frost tole rance was determined immediately after these treatments. Latitude of o rigin showed no clear pattern with respect to either frost tolerance o r 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 degrees C day:night temperature and 8-h photoperiod hardening t reatment. A low-temperature treatment of 5:5 degrees C increased the f rost tolerance of cotyledon and young seedling stage germinants, while their response to a shortened photoperiod (8 h) was quite variable. H owever, an 8-h photoperiod did enhance the effect of the low-temperatu re treatment at the young-seedling stage. Thus, the timing of germinat ion in the field appears to be an important factor in the ability of g erminants to tolerate freezing stress.