2018 ASHS Annual Conference

Several studies have suggested that postharvest needle retention in balsam fir, Abies balsamea, L increases in autumn due to cold acclimation, and that this is more evident in genotypes with lower postharvest needle retention prior to cold acclimation. It has been found that many changes occur in balsam fir during autumn months, such as accumulation of ABA, raffinose, and galactose. However, the possible roles of lipids and fatty acids (FA) in postharvest needle abscission have not been confirmed. The objective of this study was to identify if changes in polar lipids occur and if these changes are related to postharvest needle abscission in balsam fir. An additional objective was to identify any genotypic differences.

Four genotypes of balsam fir, AB-NSD-016, AB-NSD-005, AB-NSD-140, and AB-NSD-124, were sampled (x5) in the clonal orchard owned by the Department of Natural Resources, Debert, Nova Scotia, Canada at 5 time periods between September and February. Onsite testing was performed for capacitance, fluorescence, and membrane injury (MII). Samples were frozen in liquid nitrogen to store in a -80 °C freezer for later polar lipid and fatty acid analysis. The weather and photoperiod parameters were collected from the Environment Canada Weather Station located within a 2 km radius of the orchard. In addition, “sister” branches (x5) were collected at each sampling interval, transferred to the lab and hydrated to determine the mean needle abscission commencement (NAC), and average daily water usage (ADWU). The experiment was designed as a 4 x 5 factorial and analyzed using repeated measures.

AB-NSD-016, AB-NSD-005, AB-NSD-140, and AB-NSD-124 had a mean NAC of 42, 52, 32, and 75 days, respectively. AB-NSD-124 had significantly better needle retention than all other genotypes in each of the sampling periods (p = 0.000). The poorest needle abscission resistance (NAR) was the genotype AB-NSD-124. All genotypes commenced needle abscission significantly earlier when collected in February than when collected in September through December (p = 0.000), possibly related to a January thaw.

Fluorescence was significantly (p < 0.05) linked with T_{min, (}r = .881), a typical response to winter stress and reduced photosynthesis. With respect to polar lipids, there was no loss of lipids, but a redistribution of lipids as a result of exposure to decreasing temperatures and photoperiod. There was a significant (p < 0.05) decrease in the monogalactosyldiacylglycerol to digalactosyldiacylglycerol ratio (MGDG:DGDG). There were significant changes (p < 0.05) in four lipid species causing the change in the ratio: DGDG 36:6, MGDG 36:5; MGDG 36:6, and MGDG 36:7, the first two increasing and the latter two decreasing. There was an increase in the % of phosphatidylcholine (PC) and phosphatidyl ethanolamine (PE). These changes provide evidence that cold acclimation linked to lipid changes is occurring in these genotypes of balsam fir. However, there is not enough evidence to link these changes to postharvest needle abscission.