Post-harvest needle abscission is a major challenge for Christmas tree and greenery industries. It was hypothesized that ethylene triggers abscission in balsam fir. Three experiments were conducted to test this hypothesis. In experiment 1, 70 balsam fir branches were collected, placed in water, and ethylene evolution was observed over time. In experiment 2, a 2 9 5 factorial experiment was designed to determine the effect of exogenous ethylene and an ethylene receptor blocker, 1-methylcyclopropene (1-MCP), on needle abscission. In experiment 3, a 2 9 6 factorial experiment was designed to determine the effect of exogenous ethylene and an ethylene inhibitor, aminoethoxyvinylglycine (AVG), on needle abscission. It was found that ethylene evolution was the highest 1-2 days prior to needle abscission, which was consistent in untreated branches and branches exposed to exogenous ethylene. Exposure to exogenous ethylene significantly decreased needle retention by 63%. When ethylene receptors were blocked by 1-MCP, needle retention increased by 147% despite the presence of ethylene and increased by 73% in the absence of ethylene when compared to the respective controls. When endogenous ethylene synthesis was inhibited by AVG, there was no improvement in needle retention in the presence of ethylene, but there was a 113% increase in needle retention in the absence of exogenous ethylene. Ethylene is strongly implicated as the signal triggering abscission in rootdetached balsam fir.

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With the growing global urban population and the emergence of megacities, there is a huge demand for arable land to meet the food demand and reduce malnutrition. Conventional agricultural practices lead to deforestation of the land for crop production and agricultural intensification to produce higher yield per unit area. These activities have been established to have negative impact on the environment thereby causing soil and water pollution. It is important to consider the use of vertical farming technology, which utilizes both horizontal and vertical space, and efficiently uses nutrients, water, and time (off season production with artificial lighting) more effectively to produce higher yield per unit volume of space than the conventional outdoor farming. Microgreens are taken into consideration to be grown under innovative vertical farming technology since they are rich in phytonutrients and they can be harvested in a short period of time. This paper reviews the current growing conditions of microgreens in vertical farming such as crop selection, media, light, nutrient solution, and containers while identifying knowledge gaps. Further, study in this area may lead to improved growing conditions to help solve the global issues and challenges surrounding food security, safety, and resource optimization.

Earlier harvest dates have become necessary for Canadian Christmas tree producers to meet international demand, though by harvesting these trees early they may experience poor needle retention. The objective of this study is to understand the effect of harvest date on needle retention and link those changes to cold acclimation. In one experiment, balsam fir trees with varied needle abscission resistance (NAR) were collected in October and in January and monitored for needle retention. This was repeated for 3 years. In a second experiment, 45 branches were collected each month from September to January and monitored for needle retention, xylem pressure, membrane injury, capacitance, and accumulation of galactose, raffinose, and abscisic acid. High-NAR trees had little improvement in needle retention from October to January, whereas low-NAR trees had significantly improved needle retention from October to January. Between September and January, there was an 85% increase in raffinose, 147% increase in galactose, 80% increase in abscisic acid, and 62% decrease in stem capacitance. Early harvest was not detrimental for all trees, and it appears that cold acclimation is linked to postharvest needle abscission, though cold acclimation does not adequately explain differences between NAR classes.Résumé : Les producteurs canadiens d'arbre de Noël doivent récolter les arbres plus tôt pour satisfaire la demande internationale bien qu'une récolte hâtive ait un impact négatif sur la rétention des aiguilles. L'objectif de cette étude était de comprendre l'effet de la date de récolte sur la rétention des aiguilles et de relier ces changements à l'acclimatation au froid. Dans une première expérience, des sapins baumiers dont la résistance à l'abscission des aiguilles (RAA) était différente, ont été collectés en octobre et en janvier et la rétention des aiguilles a été suivie. Ceci a été répété pendant trois ans. Dans une seconde expérience, 45 branches ont été récoltées chaque mois, de septembre à janvier, pour faire le suivi de la rétention des aiguilles, de la pression du xylème, des dommages aux membranes, de la capacité électrique et de l'accumulation de galactose, de raffinose et d'acide abscissique. Il y a eu peu d'amélioration de la rétention des aiguilles d'octobre à janvier chez les arbres qui avaient une RAA élevée mais l'amélioration était significative chez les arbres qui avaient une faible RAA. Entre septembre et janvier, le raffinose a augmenté de 85 %, le galactose de 147 %, l'acide abscissique de 80 % et la capacité électrique de la tige a diminué de 62 %. La récolte hâtive n'était pas néfaste pour tous les arbres et il semble que l'acclimatation au froid soit reliée à l'abscission des aiguilles qui survient après la récolte bien que l'acclimatation au froid n'explique pas adéquatement les différences entre les classes de RAA. [Traduit par la Rédaction] Mots-clés : abscission, sapin baumier, acide abscissique, raffinose, acclimatation au froid.

Post-harvest needle loss is a major problem for balsam fir and other Christmas tree species. Recent evidence has implicated ethylene as a signal responsible for post-harvest needle abscission, but enzymological changes remain unknown. The objective of this study was to identify and quantify cellulase activity associated with endogenous and exogenous ethylene-induced abscission. An experiment was designed with three treatments (control, endogenous ethylene, or exogenous ethylene) with five replicates. Key response variables include needle retention duration, xylem pressure potential, ethylene evolution rate, and cellulase activity. Two complimentary methods were used to assess cellulase activity: a cellulose plate digestion and zymography. The results confirm ethylene as a signal for post-harvest abscission and identify ethylene-induced cellulase. Ethylene evolution was typically between 15 and 16 lL g -1 h -1 , but there was no difference among the three treatments. However, exogenous ethylene significantly decreased needle retention by 60% and resulted in a sixfold decrease in xylem pressure potential. In addition, cellulase activity increased by 8-and 12-fold in endogenous and exogenous ethylene-induced abscission, respectively, compared to the control. Identification of ethylene-induced cellulase activity has increased our understanding of the post-harvest needle abscission process and confirms ethylene's role as a signal molecule.