The Nature and Role of Volatile Terpene Compounds in Postharvest Needle Abscission, Poster Board #030

Balsam fir [Abies balsamea L. (Mill.)] is a major conifer tree in a multi-million Christmas tree and greenery industry, preferred due to its shape, blue-green color and nice fragrance. The fragrance is due to aromatic volatile terpenes, which are known to play a major physiological role in natural defense against pest infestation and mechanical injury. Studies have shown that high concentrations of volatile terpenes are synthesized in conifers but there is only limited information on the physiological role of the volatile terpenes on postharvest needle abscission. It was hypothesized that volatile terpenes promote postharvest needle abscission in balsam fir trees depending on needle abscission resistance (NAR) of a genotype. Thus, the purpose of this study was to provide a fingerprint of all the terpenes available in postharvest balsam fir.  Ten two-year old growth branches of two contrasting balsam fir genotypes that are low and high NAR and five three-year old seedlings were used for this study. Harvested branches and seedlings were sealed separately in a 4-L air tight glass jar for 30 minutes. Concentrations of volatile terpenes were determined by a head-space solid phase microextraction (SPME) procedure, followed by analysis using a gas chromatograph. Comparisons of terpene profiles showed that the high NAR genotype had 12 terpene compounds that consistently evolved in all the branches, compared to 8 and 5 terpenes for the low NAR genotype and seedlings, respectively. In addition, the total terpene concentration in the high NAR genotype was 7.3 and 16.1% higher than that of the low NAR genotype and the seedling respectively, although the low NAR genotype had higher concentration of β-pinine than the high NAR genotype. This study confirms our preliminary study that showed that the high NAR genotype has a stronger fragrance compared to the low NAR genotype or the seedling. This suggests that volatile terpenes vary in availability and concentration depending on the NAR. It is possible that some of the specific volatile terpenes have specific roles to play in promoting or inhibiting needle abscission.