Low Temperature Exposure Increases the Postharvest Needle Retention of Balsam Fir (Abies balsamea) Genotypes

Balsam fir (Abies balsamea (L.) Mill), a Christmas tree species known for its unique fragrance and pleasing architecture frequently encounters massive needle abscission and discoloration during postharvest. While, the trees are raised from seedlings that could be genetically different due to non-controlled cross pollination, anecdotal evidence attribute this deterioration in quality to the early harvesting of the trees which prevents proper hardening). Accordingly, this study was conducted to evaluate the effects of low temperature (4^oC) prior to harvest on the postharvest quality of balsam fir seedlings. A total of 200 balsam fir seedlings arising from different seed sources across Atlantic Canada were chosen for the study. Half of the population (n=100) were exposed to 4^oC (light intensity: 40 µmol.m^-2.s^-1 PAR; 60% RH) and the rest (n=100) were maintained at 22^oC temperature (PAR: 120 µmol.m^-2.s^-1; 60% RH). Following the treatments, the roots were detached from all experimental units and the shoots were transferred into 100 mL bottles containing sterile double distilled H₂O. The time until 50% of needle fall or 50% discoloration of needles, % biomass loss (fresh weight basis) and % needle loss (on a fresh weight basis) were monitored.  Seedlings from both treatments lost 46% of their fresh weight and had 1.2% needle loss at the end of the experimental period. Yet, low temperature-exposed seedlings held needles significantly longer (133 days) without discoloration than the controls (122 days) indicating that low temperature exposure can prolong postharvest needle retention by 10 days. We hypothesize that low temperature induces cold acclimation responses in balsam fir seedlings, irrespective of genotypes, which subsequently improves retention period under post-harvest conditions.